5:07

S78:E30 Sep 24, 2026

Field FBG monitoring of helicopter landing gear: data integrity screening and time–frequency characterization of operational eve

https://doi.org/10.3221/IGF-ESIS.78.30 Operational monitoring of helicopter landing gear can benefit from direct strain measurements able to resolve transient contact and roll-out dynamics. This work presents a field demonstration of a fiber Bragg grating (FBG) measurement and processing workflow applied to the main landing gear of an Erickson S-64 Skycrane operated by the Italian National Fire Brigade. Four gratings were bonded to the landing-gear structure, and wavelength data were acquired at 1 kHz during operational activities. The study does not aim to perform damage detection, health-state assessment, or hard-landing classification; rather, it evaluates whether field-acquired FBG signals affected by realistic acquisition imperfections can be transformed into interpretable time–frequency descriptors. Raw wavelength records were screened for dropouts, saturation artifacts, and spikes, then converted to normalized strain and high-pass filtered. Event-centered analyses based on Hann-window short-time Fourier transform (STFT), Thomson multitaper estimates, and ridge tracking revealed recurrent transient signatures and sensor-dependent frequency families in two representative datasets. The results support FBG-derived landing-event characterization under field conditions, while showing that synchronized avionics references, temperature compensation, and larger repeated datasets are required before validated Health and Usage Monitoring System (HUMS) or structural-integrity decisions can be made.

4:59

S78:E29 Sep 21, 2026

Design of pavements under extreme loads in challenging subsoil conditions in port areas – Case study of Szczecin and Świnoujście

https://doi.org/10.3221/IGF-ESIS.78.29 The rapid development of offshore wind energy and modern port logistics has created new challenges in the design of heavy-duty pavements subjected to extreme operational loads. This paper presents selected examples of pavement design and operational experience from the Ports of Szczecin and Świnoujście, one of the most important port complexes in the Baltic Sea region. Particular attention is given to offshore wind-related activities involving the storage, assembly, and transportation of large wind turbine components. The paper discusses the geotechnical conditions typical of the port area, including weak and organic soils, reclaimed land, and shallow groundwater conditions. Representative operational loads generated by cargo-handling equipment, RTG cranes, oversized cargo transportation systems, and offshore wind components are presented. Practical experience gained from the operation of existing port terminals is used to evaluate the performance of rigid concrete pavements and heavy-duty aggregate pavements. Selected pavement structures and ground improvement solutions are described. In addition, settlement analyses performed for an offshore wind installation terminal are presented. The results confirm that reliable pavement performance under extreme loading conditions requires detailed geotechnical investigation, appropriate ground improvement measures, and pavement solutions adapted to specific operational requirements.

6:23

S78:E28 Sep 21, 2026

A second-order relaxed Newton framework for material parameters identification and stress-constrained structural optimization

https://doi.org/10.3221/IGF-ESIS.78.28 This work presents the development and implementation of a second-order optimization algorithm based on a relaxed Newton method for the minimization of nonlinear scalar objective functions with multiple design variables. The proposed strategy combines a modified Newton scheme with a customized backtracking formulation, which explicitly enforces the Armijo sufficient decrease condition to improve convergence and stability in highly nonlinear problems and reduce computational cost. A refinement parameter is introduced to generalize the step-size sequence into a continuous form, providing a relaxation of the standard backtracking scheme. Unlike standard tuning parameters, it acts directly on the mathematical structure of the line-search procedure and remains independent of the specific physical problem, constitutive model, or objective function. The methodology is assessed through three case studies of increasing complexity, namely calibration of the Johnson–Cook plasticity model, calibration of the Gurson– Tvergaard–Needleman ductile damage model, and stress-constrained shape optimization of a hollow plate. The results demonstrate accurate parameter identification, robustness to initial guesses, and effective handling of both equality and inequality constraints through Lagrange multipliers and interior penalty functions. Comparisons with standard Newton and first-order methods, as well as Levenberg-Marquardt and Trust-Region algorithms, show better performance of the framework in terms of computational cost and number of iterations, providing an effective and computationally efficient optimization strategy for nonlinear finite element problems involving constitutive calibration and structural design.

5:26

S78:E27 Sep 20, 2026

Comparative analysis of prior austenite grain size (PAGS) determination in high grade pipeline steels

https://doi.org/10.3221/IGF-ESIS.78.27 In high‑grade casing steels operated in H2S-saturated environments, the sulfide stress cracking (SSC) is a serious concern. SSC is driven by hydrogen-coupled mechanisms that are sensitive to the microstructure formed from primary austenite. Even though the prior austenite grains (PAG) cannot be directly observed in the final martensitic / bainitic microstructure and its quantification in microalloyed fine-grained steels is complicated, there are several ways of obtaining such information. This paper compares four approaches to the estimation of prior austenite grain size (PAGS) in high-grade pipeline steels: direct measurement of grains from metallographic images after selective grain boundary etching; the lineal intercept method with chord statistics; comparison with standard plates; and the reconstruction of the parent (austenitic) microstructure based on the martensite EBSD maps using reconstruction algorithms that implement the refinement of the orientation ratio and clustering of variants in the MTEX package. The results demonstrate that even without real PAG observed by an operator, EBSD-based parent microstructure reconstruction provides several advantages over optical PAGS evaluation methods. In particular, this approach removes the dependence on the quality of selective grain-boundary etching, reduces operator-related subjectivity in grain selection, and improves the statistical representation of fine grains that may be underestimated during manual optical measurements.

5:51

S78:E26 Sep 18, 2026

Synergistic effect of Silicon Nitride nanoparticles and Hemp/Basalt hybrid reinforcement on mechanical integrity and fracture re

https://doi.org/10.3221/IGF-ESIS.78.26 Polymer composites have been a subject of extensive research for lightweight, high strength and environmentally friendly applications for advanced structures and engineering. This research aims at exploring the synergistic effect of silicon nitride (Si₃N₄) nanoparticles and alkali-/silane-treated hemp/basalt (H/B) hybrid reinforcements on mechanical properties, interfacial adhesion and fracture resistance of epoxy (Ep) composites. The hemp fibers were alkali-treated with NaOH, the basalt fibers were silane-treated, and the Si₃N₄ nanoparticles were added up to 2 wt.%. The surface modification on the fiber and uniform dispersion of nanoparticles had a significant effect on improving the structural integrity of the composites. The composite having 1.5 wt.% Si₃N₄ showed the highest interlaminar shear strength of 27.77 MPa (70.9% higher) and flexural strength of 258.91 MPa (42% higher) than the H/B F-Ep composite without Si₃N₄. The maximum fracture toughness (2.6828 “MPa.” √(“m” )) was obtained at 1 wt.% Si₃N₄, which is a 57.3% increase because of crack pinning, crack deflection and crack bridging. However, 2 wt.% Si₃N₄ led to the agglomeration of the nanoparticles and to localized stress concentrations, which slightly lowered the mechanical performance. The results show that the optimized incorporation of Si₃N₄, together with the chemically modified H/B hybrid reinforcements, is a promising approach for the enhancement of damage tolerance of the epoxy nanocomposites for lightweight structural applications in the automotive and aerospace sectors.

5:21

S78:E25 Sep 17, 2026

Fatigue damage evolution in ZrO2-reinforced Al7075 metal matrix composites: from S-N curves to Paris multilinear regimes

https://doi.org/10.3221/IGF-ESIS.78.25 Aluminum Matrix Composites (AMCs) are increasingly used in aerospace, automotive and marine applications, where structural components are often subjected to cyclic and time-varying loading conditions. A reliable assessment of their fatigue response is therefore essential for safe design and damage-tolerant applications. In this study, the fatigue behaviour of an Al7075 alloy reinforced with 1.5 wt% zirconium dioxide nanoparticles (ZrO2) is experimentally investigated, with particular attention to both fatigue lifetime and crack propagation response. The experimental programme first includes monotonic tensile tests, aimed at determining the static mechanical properties of the investigated nano-reinforced AMC and defining suitable load levels for subsequent cyclic tests. Fatigue life tests are then carried out under cyclic tensile loading at a fatigue ratio of 0.10, while fatigue crack propagation tests are performed at different fatigue ratios, namely 0.10, 0.50 and 0.75. To support the mechanical interpretation of the results, fracture surfaces are examined through optical macrographs and high-resolution scanning electron microscopy, allowing the main crack propagation and failure mechanisms to be identified. The experimental findings are compared with literature data available for both unreinforced aluminum alloys and ZrO2-reinforced AMC. The main novelty of the study lies in the integrated analysis of fatigue life, crack propagation behaviour and fractographic evidence within the same experimental framework. To the best of the authors’ knowledge, such a comprehensive investigation has not yet been reported in the literature for the composite system examined herein. While previous investigations often considered S-N fatigue response and fatigue crack propagation separately, the present work bridges these two aspects, providing a more complete description of damage evolution in ZrO2-reinforced Al7075 AMCs. This integrated dataset offers useful experimental support for the calibration and validation of fatigue damage models for nano-reinforced AMCs operating under service-like cyclic loading conditions.

5:49

S78:E24 Sep 16, 2026

Influence of mesh size, evolutionary rate, and filter radius on geometrically nonlinear topology optimization

https://doi.org/10.3221/IGF-ESIS.78.24 The BESO method is widely used to find efficient structural layouts through iterative material removal and addition. The method works well under linear conditions but things get more complicated when geometric nonlinearity is involved. Large displacements affect how the structure reaches equilibrium and this directly changes the sensitivity field and material update process making parameter selection much more critical. This paper studies three parameters systematically: mesh size, evolutionary rate and filter radius. Three benchmark structures are tested including an L-shaped beam, a pinned rectangular plate and a U-shaped plate. Each parameter is changed one at a time while the others stay fixed. Nodal displacement at the load point is used alongside topology results as a direct stiffness measure. Results show that the main load path stays intact across all tested cases but secondary bracing members are noticeably affected by coarser meshes, higher evolutionary rates and larger filter radii. The filter radius had the strongest overall influence on both topology and stiffness. The findings provide practical guidance for parameter selection and highlight the need to critically reassess algorithmic settings developed for linear BESO before applying them in large-displacement structural optimization.

4:54

S78:E23 Sep 16, 2026

The combined effect of cement matrix strength and aggregate type on the tensile behaviour of concrete

https://doi.org/10.3221/IGF-ESIS.78.23 The study investigates how the type of coarse aggregate and the strength of the cement matrix influence the splitting tensile strength of concrete. Two aggregate types commonly used in structural concrete were considered: gravel and granite. Concrete mixtures with a stronger and a weaker cement matrix were prepared in order to examine the interaction between matrix properties and aggregate behaviour during failure. The obtained results indicated that the governing factor depends on the aggregate used. In concretes containing gravel, the splitting tensile strength increased mainly with increasing matrix strength. In contrast, for concretes made with granite aggregate, the resistance to splitting was influenced to a greater extent by the mechanical properties of the aggregate itself, especially its susceptibility to crushing. To clarify the observed differences, the fracture surfaces and crack trajectories were analysed after testing. Distinct fracture mechanisms were identified for the two aggregate types. In concrete with gravel, cracking developed predominantly along the interfacial transition zone between the grains and the hardened cement mortar. For granite-based concrete, the crack path often penetrated the aggregate particles. These observations demonstrate how matrix and aggregate properties jointly determine tensile behaviour.

6:20

S78:E22 Sep 15, 2026

Study on multi-response optimization of mechanical, dielectric properties and fracture surface of alkali-treated sisal fibre rei

https://doi.org/10.3221/IGF-ESIS.78.22 This study investigates alkali-treated sisal fibre reinforced polypropylene composites produced by compression moulding, with particular attention to how fibre treatment, fibre length and fibre loading jointly influence mechanical and dielectric performance. A Central Composite Design under Response Surface Methodology was used to model tensile, flexural and impact responses and to identify a balanced processing window. Alkali treatment improved fibre–matrix adhesion by removing surface impurities and increasing fibre roughness, which strengthened stress transfer and reduced fibre pull-out. The results show that fibre loading and fibre length strongly affected the measured properties; however, excessive reinforcement or longer fibres reduced performance because of poor dispersion, void formation and local stress concentration. The regression models showed good agreement with the experimental data and were suitable for multi-response optimization within the selected design space. Dielectric measurements indicated acceptable insulating behaviour, particularly in composites with better fibre dispersion and fewer interfacial defects. SEM observations further supported these trends by revealing improved fibre embedding and reduced interfacial gaps in treated composites. Overall, the work shows that alkali treatment, combined with statistical optimization, is a practical route for developing lightweight sisal fibre reinforced polypropylene composites with balanced mechanical and dielectric properties. The novelty of this study lies in integrating mechanical characterization, dielectric evaluation, SEM-based fracture analysis and Response Surface Methodology within a single multi-response optimization framework. The optimum treated composite exhibited a tensile strength of 19.20 MPa, flexural strength of 36.20 MPa and impact strength of 178 J/m. The developed regression models showed good agreement with experimental observations, with R² values of 97.42%, 92.76%, 97.89% and 91.92% for tensile strength, flexural strength, impact strength and dielectric constant respectively.

6:05

S78:E21 Sep 15, 2026

Increasing the wear resistance of rolling bearings by laser shock peening

https://doi.org/10.3221/IGF-ESIS.78.21 Rolling bearings are among the most common components, used in virtually all branches of industry—from bicycles to space stations, including industrial and machinery equipment, automobiles, aircraft, rockets, and household appliances. Residual stresses and surface quality play a significant role in enhancing the tribological characteristics of friction pairs. Laser shock peening (LSP) is a promising method for residual stresses design, allowing for their magnitude and depth to be varied over a wide range. This study involved the LSP of friction pairs made from high-chromium bearing steel grade AISI 440-С (95Х18Ш in Russia). The results demonstrate significant improvements in tribological characteristics under both dry and boundary friction conditions. LSP led to a change in the wear mechanism, which in turn reduces wear.

5:27

S78:E20 Sep 14, 2026

Numerical investigation on web of steel I-beam with closed top flange under patch loading

https://doi.org/10.3221/IGF-ESIS.78.20 This paper studies the failure of steel beams’ webs and suggests strengthening systems. The study investigates the patch-loading resistance of I-girders with closed top-flange configurations (triangle or rectangle) formed by welding stiffener plates or angles between the web and flange edge. Non-linear finite element models are developed and validated to examine the ultimate structural response and failure modes, followed by a parametric study addressing the interaction between stiffener thickness, web thickness, and relative stiffener depth, all under variable patch loading lengths. Compact stiffeners provide a greater increase in girder strength, particularly for thin webs and short patch load lengths, whereas slender stiffeners are less effective. Increasing stiffener depth and thickness enhances load redistribution and delays web deformation. Triangular configurations generally provide higher resistance than rectangular configurations for the same added steel area. EN can calculate the web capacity for the models in the study, but to conservative side. Recommendation is to apply the actual stiffener stiffness in EN avoiding the limitation given in code. Overall, the findings provide practical guidance for selecting stiffener dimensions and closed-flange configurations to improve web resistance under patch-loading.

5:12

S78:E19 Sep 14, 2026

Strengthening techniques for progressive collapse mitigation in RC and precast structures: a selective review and the potential

https://doi.org/10.3221/IGF-ESIS.78.19 This paper presents a review of strengthening and retrofitting techniques used to improve the progressive collapse resistance of reinforced concrete (RC) and precast structural assemblies. The retrofitting strategies include fiber-reinforced polymer (FRP) systems applied as near-surface mounted and externally bonded reinforcement, steel plate systems, engineered cementitious composites and hybrid solutions. Their effectiveness has been reported in experimental, numerical and analytical studies on both full-scale and reduced-scale specimens. Although FRP-based strengthening techniques have been widely investigated, there are concerns related to debonding from the concrete surface, brittle failure and reduced performance at elevated temperatures, particularly under fire exposure. Therefore, this paper emphasizes the need to explore stainless-steel wire mesh (SSWM) as a viable and cost-effective alternative to conventional FRP materials for structural strengthening of concrete structures. The review compiles existing investigations on different SSWM-strengthened structural elements, which demonstrate improved structural response under various loading conditions. However, the application of SSWM for progressive collapse mitigation has been comparatively less explored. Therefore, this paper highlights the need to evaluate the effectiveness of SSWM in strengthening RC and precast beam-column assemblies under progressive collapse scenarios. Furthermore, the paper identifies key research gaps and outlines directions for future work, with the objective to facilitate the wider adoption of SSWM for structural strengthening and the development of guidelines for practicing engineers and researchers.

5:31

S78:E18 Sep 14, 2026

Experimental evaluation of the cyclic behavior of implanted reinforced concrete shear walls

https://doi.org/10.3221/IGF-ESIS.78.18 Adding new reinforced concrete (RC) shear walls is a widely adopted strategy for seismic strengthening of deficient RC buildings; however, the global performance of such walls depends critically on the reliability of the wall–foundation connection. This study experimentally investigates the cyclic behavior of newly implanted RC shear walls anchored to existing foundations using post-installed vertical reinforcement, highlighting the influence of embedment length. A two-stage experimental program was conducted. The first stage focused on pull-out tests to find the best adhesive type and hole diameter. In the second stage, four large-scale shear wall specimens were tested under displacement-controlled cyclic lateral loading: one control wall with cast-in-place reinforcement and three walls anchored using post-installed bars with embedment lengths of 10Ø, 15Ø, and 20Ø. The experimental results showed that variations in embedment length directly influence the lateral strength and stiffness degradation of the tested shear walls, as well as their hysteretic response and observed failure mode. Specimens with relatively short embedment lengths exhibited early interface slip accompanied by a reduction in lateral strength. Longer embedment lengths led to a shift toward flexure-dominated behavior and better cyclic performance. An embedment length of 20Ø produced a balanced combination of strength, stiffness-retention, and cyclic stability.

5:19

S78:E17 Sep 13, 2026

Microstructure-explicit Chebyshev-enriched Paris law for short fatigue crack propagation in rolled AA2024-T351

https://doi.org/10.3221/IGF-ESIS.78.17 The classical Paris-Erdogan law describes long fatigue crack propagation but fails to capture the oscillatory behaviour of short cracks in microstructurally heterogeneous materials. This work proposes an enriched Paris law based on first-kind Chebyshev polynomials for short crack propagation in rolled AA2024-T351 aluminium alloy. A normalized crack-length variable ξ = f(a/d) ∈ [−1, 1] links crack position to the average grain size d measured by EBSD. The resulting microstructural modulation factor μ(ξ) reproduces local fluctuations in crack growth rate at successive grain boundaries. The model is applied to two specimen orientations: type A (crack ⊥ rolling direction, d_⊥ = 154 µm) and type B (crack ∥ rolling direction, d_∥ = 395 µm). For type A, R² improves from 0.665 to 0.907 (N* = 21). For type B, R² improves from 0.147 to 0.835 (N* = 21). The modulation factor oscillations correlate closely with the grain boundaries identified by SEM and EBSD for type A, while for type B they suggest additional sub-surface crack-microstructure interactions linked to the pronounced difference between in-plane and through-thickness grain sizes for this orientation.

3:54

S78:E16 Sep 8, 2026

Loading biaxiality and crack tip curvature effects on plastic stress intensity factor behaviour at small-scale and extensive pla

https://doi.org/10.3221/IGF-ESIS.78.16 An elastic–plastic finite element analysis (FEA) was performed for a Mode I plane-strain center-cracked plate (CCP) made of a titanium alloy and subjected to biaxial tension/compression loading. Two crack-tip configurations were considered: a mathematical notch (MN) and a finite radius of curvature (FRC). In the present study, both the J-integral and the plastic stress intensity factor (plastic SIF) were employed to characterize the elastic–plastic stress fields near the crack tip. The distributions of the J-integral and the plastic SIF were evaluated as functions of loading biaxiality and applied stress level. The analysis covered a biaxial stress ratio range extending from equibiaxial tension–compression to equibiaxial tension and included both small-scale yielding (SSY) and extensive plasticity conditions. The results reveal a pronounced coupling between loading biaxiality and crack-tip configuration effects on the fracture parameters. Opposite trends in the variation of the J-integral and the plastic SIF with respect to the biaxial stress ratio and crack-tip geometry were observed. In addition, a comparative assessment of SSY and extensive plasticity regimes was carried out for both crack-tip configurations. It was found that under extensive plasticity conditions the plastic SIF becomes dependent on the crack-tip radius of curvature, whereas under SSY conditions it remains essentially independent of crack-tip geometry.

4:14

S78:E15 Sep 5, 2026

Effect of aging temperature on mechanical and fatigue properties of Ti-5Al-5V-5Mo-1Cr-1Fe alloy processed by radial-shear rollin

https://doi.org/10.3221/IGF-ESIS.78.15 In this study, the effect of aging temperature on the mechanical and fatigue properties of the Ti-5Al-5V-5Mo-1Cr-1Fe alloy treated by radial-shear rolling was investigated. Increasing the aging temperature from 450 up to 520 °C gave rise to coarsening of the microstructure and enhancing of the volume fraction of the -phase from 58 to 71 %. As a result, the ultimate tensile strength decreased slightly, but both ductility and fatigue performance at a cycling frequency of 5 Hz increased. In the high-cycle fatigue regime, the regularities of the initiation and propagation of cracks, as well as the evolution patterns and ultimate sizes of the fracture surface zones were revealed. In addition, both critical level of stress intensity factors and general relationships between the crack propagation and the fatigue performance were assessed. The obtained results suggested that used combinations of radial-shear rolling and subsequent aging is a promising treatment for critical components made of the Ti-5Al-5V-5Mo-1Cr-1Fe alloy operated under low-frequency high-amplitude loads.

6:38

S78:E14 Sep 5, 2026

Experimental and numerical modelling of AISI 316L Butt-welded joints under tensile stress using local material properties

https://doi.org/10.3221/IGF-ESIS.78.14 The mechanical characterization of welded joints is a critical step in assessing the structural reliability of stainless-steel components employed in marine, offshore, and industrial environments. Welding processes introduce significant local variations in microstructure and hardness, leading to heterogeneous mechanical properties that strongly influence fatigue life and structural performance. This study presents an integrated experimental–numerical methodology for the evaluation of local mechanical properties in AISI 316L butt-welded joints through minimally destructive hardness measurements. The approach combines two established hardness–property correlations to derive full true stress–strain curves for each region of the weld. These were subsequently implemented in a finite element model to reproduce the local and global deformation behavior during quasi-static tensile loading. Calibration was achieved using tensile tests on non-welded specimens, and a preliminary validation was conducted through Digital Image Correlation (DIC) strain measurements of both welded and base material specimens. Unlike most existing studies that focus on structural steels, this work investigates AISI 316L welds, austenitic stainless steel widely used in high-integrity applications, through a combined microhardness–FEM–DIC framework. The proposed methodology suggests the possibility to develop robust framework for correlating indentation hardness with mechanical response, offering a rapid, reliable, and potentially non-destructive route for assessing welded structures.

4:56

S78:E13 Aug 30, 2026

Crystal plasticity modeling of perfectly bonded layered composites under combined normal/shear loading

https://doi.org/10.3221/IGF-ESIS.78.13 The paper addresses an actual fundamental mechanical problem – analysis of deformation behavior of a perfectly bonded layered metallic composite consisting of soft and hard components, being subjected to normal load and shear stress under mechanical equilibrium at prohibited interfacial slip. The problem is solved with the use of 3D crystal plasticity (CP) simulations using the DAMASK Spectral Solver package. By doing so, microstructure-inherited stress and strain fields were calculated, visualized, and analyzed. The results obtained provide an insight into the patterns of stress and strain localization as well as their evolution within and between mated soft/hard phases with different microstructure at the onset of subsurface deformation processes. The latter corresponds to the pre sliding regime beneath dry tribological contact zones. The resulting effective shear-to-normal stress ratio responses exhibited significant differences that depend on the microstructure and mechanical properties of both interfaced materials that compose a tribological pair.

5:32

S78:E12 Aug 21, 2026

The effect of external service-induced defects on the mechanical properties of fibreglass-reinforced plastic under compression

https://doi.org/10.3221/IGF-ESIS.78.12 Methods have been developed for inducing service-related defects—dents (using flat and spherical indenters) and scratches (using a steel blade)—under controlled impact conditions, based on the combined use of a testing system and an acoustic emission signal recording system. Critical values of loads and displacements have been established for each type of indenter (induced defect). A 4 mm thick STEF model fiberglass laminate was used as the test material. Samples measuring 150 mm × 20 mm × 4 mm were cut from the sheet of material in the warp and weft directions. Simulated external defects were applied to the specimens: a dent at a load of 0.85 times the breaking load, and a scratch at a load of 1 kN and a depth of 0.5 mm. Compression tests (ASTM D 3410/GOST 33519—2015) were carried out on groups of specimens cut along the warp and weft, without defects, and with defects including a cylindrical indentation, a spherical indentation and a scratch. The test results showed that the most dangerous defect is the ball indentation, which leads to a 20% reduction in compressive strength for weft-direction samples and a 12% reduction for warp-direction samples. Scratches and cylinder indentations had virtually no effect on the compressive strength values, and the difference in values can be explained by statistical variation. Acoustic emission signals were also recorded and analyzed during the compression testing.

4:35

S78:E11 Aug 18, 2026

Effects of seawater corrosion, notch timing, and test temperature on the impact toughness of AISI 1008 marine chain steel

https://doi.org/10.3221/IGF-ESIS.78.11 Marine chains operate under corrosive and impact-prone conditions, yet the combined influence of seawater exposure, notch condition and test temperature on their impact toughness remains insufficiently clarified. This study addresses this gap by examining the Charpy V-notch impact response of AISI 1008 steel extracted from galvanized marine chain links after exposure to seawater and substitute seawater. Rather than treating corrosion damage only as mass loss, the study focuses on how corrosion history, notch timing and local material variability jointly affect absorbed impact energy. The results showed a pronounced temperature sensitivity in the uncorroded condition, with absorbed energy decreasing sharply from room temperature to sub-zero temperatures. After 30 days of immersion, both seawater and substitute seawater reduced the average impact energy at 0 °C, while seawater produced higher mass loss. However, the absorbed energy did not scale directly with corrosion loss. Considerable scatter was observed even under nominally identical conditions. Near-fracture cross-sectional SEM highlighted local ferrite–pearlite heterogeneity and discontinuity-like features in selected regions. The findings demonstrate that the impact resistance of the investigated marine chain steel cannot be assessed solely from average corrosion loss or hardness values, and highlight the need to consider notch condition, temperature and microstructural variability in structural integrity evaluations.

4:57

S78:E10 Aug 15, 2026

Investigating the effects of steel fibers and notch depth on the fracture behavior of reinforced concrete (RC) beams using both

https://doi.org/10.3221/IGF-ESIS.78.10 Steel fibers are commonly used to compensate for the tensile weakness of concrete. However, the interaction of steel fibers with conventional reinforcing bars after a crack has been formed is poorly understood. Most fracture studies use a cut through the thickness of the material that cuts through any fiber in its path, whereas a real crack would maintain the bridging action. In this study, the true mode I fracture toughness (KIC) of steel-fiber-reinforced concrete beams with longitudinal steel bars is determined using a matrix-crack (MC) approach where short fibers are not broken through a natural pre-crack, and compared with companion beams prepared with a conventional through-thickness crack (TTC). Reinforced concrete (RC), normal strength concrete (NC), and fiber-reinforced concrete (FRC) beams with a steel fiber volume fraction of 1.0%, two ratios of notch depth to beam depth (a/d=0.25 and 0.5), and two reinforcement layouts were tested under four-point bending. Incorporation of steel fibers delayed crack propagation and improved ductility, increasing the ultimate load-carrying capacity by up to 50% and the modulus of toughness by nearly 94% relative to fiber-free beams. All cases showed higher first-cracking loads and better post-cracking load maintenance for MC specimens than for TTC specimens, confirming that the MC approach provides a more realistic representation of fiber bridging. KIC increased with a/d in plain reinforced beams, due to the growing moment arm of the steel closing force, but decreased with a/d in fiber-reinforced beams, indicating that fiber-bridging efficiency weakens as the crack deepens. The results support the MC method as a more reliable approach for assessing the intrinsic fracture toughness of fiber-reinforced RC members.

5:55

S78:E09 Aug 13, 2026

Development and performance evaluation of hybrid nano modified SCM-based concretes

https://doi.org/10.3221/IGF-ESIS.78.09 Concrete production contributes approximately 8-10% of global CO₂ emissions necessitating sustainable alternatives. This study investigates hybrid nano-modified composite cement concrete with Ordinary Portland Cement (OPC) partially replaced by Ground Granulated Blast-furnace Slag (GGBS, 30-35%) and Fly Ash (10-15%) by weight of cement, nano-reinforced using Graphene Oxide (GO, 0.01-0.05%) and Carbon Nanotubes (CNT, 0.1-0.3%) by weight of cement. Eight mixes were designed and evaluated for fresh properties, mechanical performance (compressive, split tensile, and flexural strength at 7, 28, and 56 days), and microstructure (SEM, XRD, and EDAX). Nanomaterials were dispersed using magnetic stirring to ensure uniform distribution. Optimal formulations achieved significant enhancements, specifically, GO 0.03% reached 34.5 MPa compressive (+23.2%) and 15.6 MPa flexural (+108%); CNT 0.1% achieved 33.53 MPa compressive (+19.8%) and 3.23 MPa tensile (+31.8%); the hybrid (GO 0.03% + CNTs 0.1%) demonstrated 33.9 MPa compressive (+21.1%) and 14.92 MPa flexural (+98.9%). Early-age strength improved by 69-77%, compensating for slower pozzolanic reactions associated with GGBS and Fly Ash. Microstructural characterization revealed densified C-S-H gel, refined ITZ (from 20-50μm to 10-15μm), reduced porosity (from 12.3% to 7.8%), enhanced crystallinity, and optimal Ca/Si ratios (1.36-2.14). Environmental assessment showed 39.2% CO₂ reduction and a 50.7% improvement in carbon intensity. The hybrid approach provides a viable route to sustainable, high-performance concrete for infrastructure applications.

4:24

S78:E08 Aug 12, 2026

Comparative study on dry wear and tribocorrosion behavior of boronized martensitic stainless steels

https://doi.org/10.3221/IGF-ESIS.78.08 The tribocorrosion behavior of boronized 13Cr4Ni and 16Cr5Ni martensitic stainless steels (MSS) in 3.5 weight percent NaCl is examined in this work. Samples were tempered at 600 °C for two hours and boronized at 950 and 1000°C for six hours. Hard surface layers (≈1680–1805 Hv) with case depths of 35-90 µm were generated by boronizing. Icorr increased from 0.6-0.9 µA/cm² (bare) to 4.3-8.1 µA/cm² (boronized) and then to 14.3-27.1 µA/cm² under tribocorrosion. Potentiodynamic polarization showed a shift in corrosion potential by around 200–310 mV toward more active values. The coefficient of friction (COF) in dry sliding varied from 0.49 to 0.78, and wear rates ranged from 3.5 to 5.1 × 10⁻6 mm³/Nm. At 950 °C, wear rates decreased by 25 to 27% because of higher fracture toughness (3.3 to 3.9 MPa√m). Due to electrolyte lubrication, COF decreased to 0.28-0.49 (16-33% lower) under tribocorrosion. When compared to bare MSS, boronized samples showed noticeably better wear resistance, with wear reduction of 60-80%. Under tribocorrosion, wear mechanisms changed from sticky abrasive in dry sliding to mixed abrasion, adhesion, and tribo-oxidation, controlled by cyclic passivation–depassivation. Boronizing, particularly at 950°C, improves overall tribocorrosion performance despite decreased corrosion resistance by balancing hardness and toughness.

5:13

S78:E07 Aug 11, 2026

Optimal shape determination of shear specimens using Machine Learning

https://doi.org/10.3221/IGF-ESIS.78.07 Shear strength represents an important mechanical property. For the additively manufactured polymers nowadays, there is not a valid standard to determine the shear strength. Finite element analysis of 145 shear specimen geometries was performed. Then an AI-based optimal shape prediction methodology was developed using supervised machine learning, where a Multiple Linear Regression model was trained on selected design parameters to accurately predict shape performance and efficiently explore new design configurations. The ratio between maximum shear stress and maximum normal stress in the shear plane was considered the parameter to be optimized.

4:34

S78:E06 Aug 3, 2026

Influence of impact energy on residual stresses values inherent in damaged area of composite plate

https://doi.org/10.3221/IGF-ESIS.78.06 The dependences connecting the values of the residual stress components in the contact interaction zone of the steel indenter and the surface of the composite plate with the impact energy are presented. These quantitative relations are first obtained on the basis of an original experimental method developed earlier by the authors of this article. It is also established that the upper limit of applicability of the developed approach to residual stress quantifying has been expanded to the impact energy of 75 J. New results are presented that make it possible to estimate the distribution of the residual stress components over the thickness of the composite plate. The required results are obtained by drilling probe holes from the side opposite to the contact dimple. These data are essential to create a methodology for assessing the residual strength of composite plates with impact damage based on the use of residual stress values as a design parameter.

4:46

S78:E05 Jul 25, 2026

Effect of layer orientation and infill density on reliability and lifetime of FDM-printed conductive composites under tensile lo

https://doi.org/10.3221/IGF-ESIS.78.05 Conductive composites have attracted growing interest in recent years in the field of additive manufacturing, especially for functional and structural applications. Nevertheless, their mechanical behavior and durability remain highly influenced by 3D printing methods and parameters. This paper investigates the combined effect of layer orientation and infill density on the mechanical damage and reliability of PLA-CB conductive composites manufactured by filament deposition modeling (FDM) technology. Tensile tests were performed on specimens printed with different layer orientations (0°, 45° and 90°) and infill densities (20%, 40%, 60%, 80% and 100%) to analyze the evolution of damage and the dispersion of mechanical properties. Analysis of damage evolution was used to model failure probability, assess material reliability, and predict service life based on 3D printing parameters. The results indicate that infill density significantly influences mechanical strength and performance stability, while layer orientation also plays a key role in the failure mechanism. The 0° orientation (parallel to the tensile direction) offered the best mechanical performance. At 45°, the results show intermediate behavior between stiffness and flexibility due to the distribution of shear stresses between layers. However, samples printed at 90° show much lower strength, dominated by delamination between layers. This study thus proposes a useful predictive framework for optimizing the printing parameters of PLA-CB conductive composites and contributes to a better understanding of their behavior in service for applications requiring reliable and durable mechanical performance.

5:29

S78:E04 Jul 15, 2026

Fatigue damage assessment for Sine-on-Random: a comparative analysis of the predictive capability and application limits of spec

https://doi.org/10.3221/IGF-ESIS.78.04 Mechanical and electronic components, mainly in aerospace and rotating machinery environments, are generally subjected to Sine-on-Random (SoR) excitations, where deterministic sinusoidal tones are superimposed on a broadband random vibration. While international testing standards require the validation of components under these complex profiles, the numerical evaluation of fatigue damage poses a major analytical challenge. The time-domain rainflow counting method is computationally prohibitive. Conversely, frequency-domain spectral methods rely on Gaussian assumptions that are explicitly violated by SoR loads, leading to inaccurate damage estimates. To bridge this gap, researchers have developed two main strategies: practical approaches that synthesize an equivalent random Power Spectral Density (PSD) based on damage or energy equivalence, and rigorous theoretical methods deriving analytical cycle distributions. This paper evaluates and compares the available methodologies, aiming to highlight the benefits and limitations of each. Ultimately, this comparative study serves as a practical guide for engineers to select the most appropriate tool for fatigue damage assessment under SoR vibrations.

5:46

S78:E03 Jul 14, 2026

Mechanical and fracture response of epoxy nanocomposites reinforced with low concentration graphene and graphene–SiO₂ hybrids

https://doi.org/10.3221/IGF-ESIS.78.03 Epoxy adhesives are known to have good strength and chemical resistance; however, they tend to be brittle, restricting their use in structural applications. This study examines the effect of low-concentration graphene and hybrid graphene–SiO₂ reinforcement on the mechanical and fracture behaviour of epoxy nanocomposites. Composites containing 0.1–0.4 wt.% graphene and hybrid systems with 0.05–0.2 wt.% graphene combined with SiO₂ were synthesised using in-situ polymerisation and ultrasonic dispersion to ensure uniform filler distribution. Tensile, flexural, and fracture tests were performed following ASTM standards. The mechanical properties of epoxy composites are significantly improved by adding nano fillers when used at optimal concentrations. From the single filler systems, epoxy with 0.3 wt. % graphene achieved the highest enhancement of tensile and flexural strengths compared to pure epoxy. Greater enhancement was also found in the hybrid composites with a combination of 0.15 wt.% graphene and 0.15 wt.%. SiO2 resulted in an increase of 53% and 22% for tensile strength and flexural strength, respectively. All nano composite specimens showed a higher fracture toughness, with the best improvement of 71.1% found for the composite mix containing 0.2 wt.% graphene and 0.2 wt.% SiO2. Scanning Electron Microscopy (SEM) images indicated stronger interfacial bonding, more crack deflection and less brittleness when the filler loadings were optimized. The excessive filler content caused agglomeration due to which the performance was lowered. The structural strength and fracture resistance of the epoxy nanocomposites were significantly improved when Graphene is combined with SiO2 and this combination created a strong synergistic effect. A finite element simulation was carried out to understand the impact of filler addition on the flexural strength of nanocomposites and results were compared with experimental outcomes.

4:53

S78:E02 Jul 12, 2026

Heat treatment of steel using Carboxymethyl Cellulose (CMC) as a green quenching medium: effect of concentration on microstructu

https://doi.org/10.3221/IGF-ESIS.78.02 Quenching has always been an important heat treatment that alters the mechanical and morphological properties of various types of steel. Different quenching media have been used depending on the operating conditions and desired properties, as each quenching medium affects the resulting properties and microstructure. Various types of quenching media have been used to study their effects, including oils, polymers, and water-based mixtures. In this study, an environmentally friendly, water-soluble polymer quenching medium (Carboxymethyl cellulose sodium salt (CMC)) in different concentrations was used to investigate its effect on the morphology and the mechanical properties of 1020 steel as a quenching medium in future industrial and engineering applications. 0.1% wt CMC polymer as a green quenchant enhances wear resistance despite lower hardness, confirming that microstructure and adhesive wear mechanism affect the tribological behavior rather than hardness alone.

5:36

S78:E01 Jul 12, 2026

Experimental and numerical investigation of residual stresses in dissimilar butt-weld joint made of cast iron and mild steel

https://doi.org/10.3221/IGF-ESIS.78.01 Joining dissimilar metals like cast iron and structural steel offers great design flexibility, but it can be a structural nightmare. Different thermal expansions and conductivities during welding create severe residual stresses and distortions, threatening the integrity of hybrid components. Our latest research introduces an experimentally validated Finite Element (FE) model for Cast Iron-Steel butt welds. We discovered a striking asymmetry: the steepest thermal gradients and the highest longitudinal residual stresses localize predominantly on the cast iron side due to its microstructural hardening, rather than the steel. Want to optimize your hybrid structural designs and avoid unexpected failures? Read the full open-access paper to explore our predictive thermo-mechanical modeling approach!