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!