5:48

S77:E24 Jun 14, 2026

Mechanical, tribological and fractography analysis of structural grade Al7075/n-TiC composites and optimization of wire EDM para

https://doi.org/10.3221/IGF-ESIS.77.24 The effects of nanoscale TiC (n-TiC) reinforcement on Al7075 composites made by stir casting with 0%, 1%, 2%, 3%, and 4% reinforcement are examined in this work. The existence of n-TiC particles in the aluminum matrix was verified by microstructural investigation. When compared to un-reinforced alloy (Al7075), the mechanical, tribological, and wear properties were greatly improved by the addition of n-TiC; hardness, tensile strength, and wear resistance increased by 28.57%, 24.41%, and 33.69%, respectively. Molybdenum wire was used as the electrode material in an experimental investigation of the produced nano composites’ machinability characteristics during Wire Electrical Discharge Machining (WEDM). Two machining attributes, Material Removal Rate (MRR) and Surface Roughness (SR), are examined in connection to the combinational values of pulse time ON, pause time OFF, as well as peak current, which are chosen as the changeable input process elements. The results of the experiment showed that as pulse on time and peak current levels increased, so did MRR and Ra values. Under these circumstances, the wire electrode has maximum current, which makes it simple to remove more material and produce a moderate surface finish. The ANOVA results show that the “Pulse ON Time” has the biggest impact (47.01 %) on MRR and 36.64% impact on surface roughness values compared to the other factors, making it the most important parameter. The confirmatory test results revealed that the errors in MRR and Ra values were within acceptable limits. In the present research work, Taguchi methods have been successfully implemented to identify the optimum machining conditions for Al7075/n-TiC composites.

5:05

S77:E23 Jun 14, 2026

From microhardness to fatigue life: a review of predictive approaches for surface-hardened mechanical components

https://doi.org/10.3221/IGF-ESIS.77.23 This review paper aims to systematically examine the effects that the most common thermal and thermochemical surface hardening treatments - specifically surface hardening, carburising, and nitriding - have on the fatigue strength of mechanical components, which has historically been the primary cause of failure during service. Following a brief description of the heat treatments and the mechanical and metallurgical effects they produce on components, a predictive model of the fatigue strength of surface-hardened mechanical components subjected to bending stresses is presented, using the local fatigue limit approach. The parameters used in the model are the microhardness profile of the hardened zone, the distribution of residual stresses in the hardened layer, the fatigue strength of the base material, and the stress state induced by external forces. The proposed model was validated for three real-world cases: surface hardened specimen with a notch, smooth carburised specimen and smooth nitrided specimen. The results provide important insights from both an academic and industrial perspective. In fact, they allow for the determination of which parameters must be controlled to increase the fatigue strength of surface-treated mechanical components.

4:57

S77:E22 Jun 13, 2026

Fatigue behavior of 17-4 PH parts produced by Material Extrusion Additive Manufacturing: A study on thickness and notch effects

https://doi.org/10.3221/IGF-ESIS.77.22 17-4 PH specimens were produced using the three-step process referred to as Material Extrusion Additive Manufacturing (MEAM), which involves printing components with a composite feedstock of metal powder and polymers, followed by a debinding process to remove the polymer, and a final sintering process to obtain the finished metallic part. The process enables the production of metallic components at a limited cost and with reduced safety issues in comparison to other additive manufacturing processes. With the goal of exploring and evaluating the fatigue properties of 17-4 PH MEAM specimens, two experimental campaigns were designed. The first with the objective of assessing the effect of thickness on the fatigue performance of smooth specimens, and the second aimed to investigate the notch effect on the fatigue limit of different notched specimens. The smooth specimens were fabricated with a thickness ranging between 1 and 5 mm, while the notched specimens were fabricated with a thickness of 3 mm, with 90° and 30° notch opening angles. The mechanical properties of the smooth series proved not to be affected by the thickness, neither for quasi-static nor cyclic response. On the contrary, the fatigue behavior of the notched specimens was significantly influenced by the presence of the notch, with sharper notches exhibiting a more negative impact. Moreover, the findings revealed that the fabrication of specimens characterized with thin sections, small geometrical features, and acute notches presented significant challenges, posing a severe issue regarding the practical applicability of MEAM for real-life complex geometries.

6:13

S77:E21 Jun 5, 2026

Influence mechanism of defects in aluminum alloy friction stir welding on fatigue life

https://doi.org/10.3221/IGF-ESIS.77.21 By controlling welding parameters and adjusting process conditions, three typical defects-oxide inclusions, tunnel defects, and lack-of-penetration defects-were intentionally introduced during the friction stir welding (FSW) of aluminum alloys. A comparative analysis of fatigue S-N curves between sound joints and joints with the three types of defects was conducted to systematically evaluate the impact of different defect types on the fatigue performance of welded joints. The results demonstrated that all three defects significantly reduce the fatigue life of the joints, with lack-of-penetration defects having the most pronounced effect, followed by tunnel defects and oxide inclusions. Fracture surface analysis using SEM, EDS, and Microhardness testing confirmed that defects act as the primary crack initiation sites—the sound joint initiated cracks at the arc-textured surface, whereas cracks in all defective joints originated from the defect regions. Building on these fractographic findings, the intrinsic micro-mechanism responsible for the systematic decrease in the S-N curve slope —from 7.14 for the sound joint to 2.74 for the LOP defect joint—was elucidated: the geometric sharpness and interfacial bonding state of a defect compress the crack initiation stage, shifting the dominant failure mode from initiation-dominated to propagation-dominated, which in turn manifests as a reduction in m .

4:56

S77:E19 May 25, 2026

Parametric analysis of carbon nanofiber effects on mechanical properties and abrasion resistance of GF/PPS hybrid composites

https://doi.org/10.3221/IGF-ESIS.77.19 The focus of this research was to investigate the effects of carbon nanofiber (CNF) reinforcement on the mechanical performance, interfacial characteristics, and abrasive wear behavior of short glass fiber/polyphenylene sulfide (GF/PPS) hybrid nanocomposites intended for high-performance tribological applications. Melt processing was used to fabricate GF/PPS hybrid nanocomposites with 0, 0.4, and 0.8 wt% CNFs, which were then methodically characterized. Through π–π interactions between CNFs and the polymer matrix, FTIR measurements demonstrated enhanced interfacial compatibility while confirming the retention of the PPS chemical structure. The addition of CNFs demonstrated improved fiber–matrix adhesion and load transmission capability by increasing composite density, decreasing void content, and considerably improving interlaminar shear strength (23.7%) and hardness (20%). Studies on two-body abrasive wear showed significant decreases in wear loss and coefficient of friction (CoF), with the 0.8 wt% CNF-filled composite showing the best tribological performance because a stable and continuous lubricating tribo-film was formed. Applied load mostly controlled the CoF behavior, while sliding velocity and abrasive grit size primarily affected wear loss, according to statistical ANOVA data. With prediction errors under 6.5% and coefficient of determination (R²) values between 73% and 77%, regression models demonstrated strong predictive power. The change from severe micro-cutting, matrix deterioration, and fiber pull-out in unfilled composites to mild ploughing and protective tribo-layer development in CNF-reinforced composites was further validated by worn surface morphology. The CNF modified GF/PPS hybrid nanocomposites are promising materials for automotive transmission components, bearing cages, thrust washers, gears, and power plant chute liners operating under extreme abrasive wear conditions, as evidenced by the synergistic improvement in mechanical strength, interfacial bonding, and tribological stability.

4:05

S77:E18 May 23, 2026

Validation of Notch-Stress Intensity Factor, Strain Energy Density and Effective Notch Stress approaches in fatigue life assessm

https://doi.org/10.3221/IGF-ESIS.77.18 The purpose of this work is to validate the N-SIF (Notch-Stress Intensity Factor), SED (Strain Energy Density) and ENS (Effective Notch Stress) approaches for the fatigue design of austenitic stainless steel welded joints. Literature fatigue data for cruciform welded joints, originally expressed in terms of nominal stress, were first re-analysed through a finite element model in terms of N-SIF. The resulting fatigue limit was then used to determine the SED critical radius required for the application of the SED approach. The same dataset was subsequently reprocessed in terms of SED. Finally, a second finite element model was implemented to calculate the ENS values. The N-SIF and SED approaches led to a more unified representation of the fatigue behaviour compared to nominal stress, showing a noticeable reduction in data scatter. In contrast, the ENS method exhibited a significant dispersion for the investigated joints, possibly due to material-specific effects and to the geometric regularisation introduced by the fictitious notch radius. Although the available dataset is limited to root failures in cruciform joints, the results suggest promising applicability of fracture-mechanics-based local approaches to austenitic stainless steel welded joints, while indicating that further validation of the ENS method is required.

6:01

S77:E17 May 21, 2026

Effect of ultrasonic welding conditions and energy director thickness on structure and properties of lap-joints of PEEK-based co

https://doi.org/10.3221/IGF-ESIS.77.17 The aim of this study was to investigate the effect of thickness of energy director (EDs) and ultrasonic welding (USW) process parameters on structure formation and interlaminar shear strength (LSS) values of lap-joints of composite polyetheretherketone (PEEK) based plates reinforced with 40 wt. % short carbon fibers (SCF). The null hypothesis was the necessity of complete melting and extrusion of the EDs from the fusion zones to ensure the minimal presence of discontinuities at reaching the maximum LSS value. During the USW with a flat anvil, frictional heating developed primarily along the periphery of the fusion zones due to less strict constraint conditions. The rational process parameters were the ED thickness of 100 μm and the USW duration of 800 ms, which enabled the formation of the fusion zones over the 62.5 % of the contact region. The LSS values of >11 MPa with the load at failure of >4500 N developed through the base material due to bending of the adherends. The use of a spherical anvil localized frictional heating and fusion in the center of the clamped region. Without EDs, the lap joints achieved the maximum stress at failure of >60 MPa; however, the small fusion zone area limited their load-bearing capacities to 3000 N. The multi-spot lap-joints of the adherends from the PEEK/SCF composite formed without EDs were characterized by the structural integrity, while the stress at failure was equal to ~30.8 MPa, which were 2–3 times higher than those with the EDs 100 and 250 μm thick. The structure of the multi-spot-welded joints was determined by the ratio of the ED thickness to the distances between adjacent spots. Inserting the EDs significantly enlarged the fusion zone area, but uneven distributions of the clamping force resulted in their different melting and spreading patterns, giving rise to in discontinuities in the formed structure. The optimization of USW procedures for fibrous PEEK/SCF composites should be aimed at achieving a balance between the distances between adjacent spots and the ED thickness to ensure control of melting the polymer in fusion zones (outside the clamped region) and to eliminate the formation of discontinuities caused by its deficiency due to squeezing out.

3:58

S77:E16 May 6, 2026

Study of the influence of recycling aluminum on the cyclic material behavior for chill cast AlSi7Mg0.3

https://doi.org/10.3221/IGF-ESIS.77.16 Automotive industry and mechanical engineering strive to drastically reduce the carbon footprint of their products. This becomes increasingly important as aluminum usage grows for lightweight, efficient components. Nevertheless, cast aluminum products suffer from a lack of alloys bearing higher fractions of recycling content, though their availability is crucial. Using recycling aluminum in gravity die casting offers high potential for CO2 reduction, but the effect of increasing accompanying elements like Cu, Zn or Fe on cyclic material behavior has not been investigated yet. Within the Fraunhofer internal research project “FutureCarProduction,” the effects of secondary aluminum alloys on casting processes as well as fatigue and crash behavior of car body components are investigated. The aim is to find the optimal combination between manufacturing efficiency and durability regarding the alloy’s potential to reduce carbon footprint and emissions during the product life cycle. Based on alloy AlSi7Mg0.3 used in gravity die casting for car body components, three configurations — one primary alloy and two with accompanying elements — were cast and investigated through strain and stress-controlled tests. Results showed that additions of Fe and Zn lead to slightly increased cyclic and quasi-static material strength, whereas ductility was reduced.

5:47

S77:E15 May 5, 2026

Stress Intensity Factor solutions for through-clad and underclad defects in WWER reactor pressure vessel nozzles under pressuris

https://doi.org/10.3221/IGF-ESIS.77.15 This study develops stress intensity factor (SIF) solutions for cladded WWER reactor pressure vessel nozzles subjected to pressurised thermal shock loading. Although finite element analysis is widely used for fracture assessment, analytical or semi-analytical SIF formulations remain important for fast evaluation, including online stress monitoring, probabilistic fracture mechanics, and screening of transient scenarios. The proposed approach combines an influence coefficient method based on three-dimensional finite-element J-integral evaluation with least-squares refinement of shape coefficients. A stress decomposition procedure is applied to address the stress discontinuity at the ferritic base metal–austenitic cladding interface. The resulting coefficients are validated against finite element reference solutions for representative pressure and thermal loading cases and show good agreement over the investigated range of crack sizes and aspect ratios. The developed solutions provide a practical tool for engineering assessment of through-clad and underclad defects in cladded WWER nozzle regions.

4:38

S77:E14 May 5, 2026

Modeling subgrain structure evolution during heat treatment

https://doi.org/10.3221/IGF-ESIS.77.14 This paper presents a novel modification of the multilevel statistical model for describing the subgrain boundary migration that can explicitly account for the topology of subgrain structures in the form of Laguerre polyhedra. The evolution of a representative volume of subgrains during annealing in the temperature range after plastic deformation taking into account competing recovery processes like coalescence and subgrain boundary migration is modeled. The material used in this study is the nickel-based superalloy Inconel 718 with complex hierarchical structure and specific phase composition. The results of modeling the changes in a polyhedral subgrain structure under recovery are presented. The contribution of subgrain coalescence and migration processes to recovery is evaluated. The abnormal growth of subgrains is described by the model, the conditions of its occurrence and implementation are defined. The calculated data demonstrate good agreement with experimental results.

4:41

S77:E13 May 3, 2026

Flexural performance of FDM-fabricated PLA composites reinforced with short carbon fiber

🔗 https://doi.org/10.3221/IGF-ESIS.77.13 🤔 Fused Deposition Modeling (FDM) is transforming manufacturing, but its default material—neat PLA—lacks the stiffness and flexural strength required for demanding structural applications. 💡 Recent research demonstrates that reinforcing PLA with short carbon fibers significantly enhances its mechanical performance. Incorporating just 6 wt% carbon fiber yields an impressive 88% increase in flexural strength (reaching 109 MPa) compared to neat PLA, effectively redistributing bending stress. 🗞️ Want to learn how microstructural integration in these composite filaments can optimize lightweight components? Read the full study to explore the fracture mechanisms and mechanical data! #AdditiveManufacturing #PolymerComposites #CarbonFiber

5:07

S77:E12 Apr 29, 2026

Preparation and enhanced mechanical properties of epoxy resin modified with pyrolysis bio-oil

https://doi.org/10.3221/IGF-ESIS.77.12 This study investigates the modification of epoxy resins with pyrolysis bio-oils derived from plant waste, aiming to enhance mechanical performance. A method for epoxy resin modification using bio-oil is proposed, including techniques for bio-oil pretreatment, purification, and incorporation into epoxy resin. Three pyrolysis bio-oils (birch, sunflower, and a mixed softwood and hardwood feedstock) across different concentrations were used as a modifier. Mechanical properties were evaluated under tension, compression, and three-point bending loading. Mechanical testing revealed that epoxy resin modified with the bio-oil at an optimal concentration of 12.5 phr produced polymer system with strength characteristics comparable to epoxy resins modified with an industrial plasticizer, while demonstrating superior compressive strength properties. Combined modification with bio-oil and industrial plasticizer dibutyl phthalate resulted in enhanced both deformation and ultimate stress levels for all types of loading considered. The bio-oil derived from the mixed wood feedstock can effectively replace the dibutyl phthalate in terms of mechanical performance while providing additional benefits in environmental sustainability and cost efficiency.

5:37

S77:E11 Apr 25, 2026

Mechanical characterization and crack propagation in Additively Manufactured Polymers using Digital Image Correlation: a review

https://doi.org/10.3221/IGF-ESIS.77.11 While Additive Manufacturing (AM) of polymers has matured from rapid prototyping to functional production, the layer-wise fabrication process introduces significant mechanical anisotropy and microstructural heterogeneity, which complicates conventional mechanical characterization. This review examines the applicability of Digital Image Correlation (DIC) as a full-field, non-contact metrological tool for mapping strain with sub-pixel precision across three domains: (1) the fundamental metrological principles of DIC applied to anisotropic AM structures, (2) a critical synthesis of DIC applications in tensile, fracture, fatigue, and impact testing, and (3) emerging advances in data acquisition, including in-situ monitoring and AI-driven frameworks. DIC uniquely enables the direct visualization of localized strain concentrations at filament interfaces and non-ideal crack propagation paths that conventional point-wise sensors obscure. Technological maturation is increasingly driven by Deep DIC frameworks and neural operators ( DisplacementNet, StrainNet), which now integrate with automated defect tracking systems. Furthermore, multimodal approaches combining DIC with Acoustic Emission (AE) and Micro-Computed Tomography (µ-CT), alongside volumetric Digital Volume Correlation (DVC), extend damage characterization from surface observations to internal defect evolution. To support industrial certification in safety-critical sectors, the community must adopt standardized metrological baselines, including the Metrological Efficiency Indicator (MEI) and the iDICs Good Practices Guide. These protocols will bridge the gap between as-designed simulations and as-built experimental validation, positioning DIC as a foundational technology for Industry 4.0 and NDE 4.0 paradigms.

5:53

S77:E10 Apr 22, 2026

Phenomenological models of residual mechanical properties of polymer composites under fatigue loading: review, analysis of descr

https://doi.org/10.3221/IGF-ESIS.77.10 In this work, a review and mathematical analysis of phenomenological models of residual strength and residual stiffness of polymer composite materials under fatigue loading have been carried out. The methodology of the analysis is described in detail, including various approaches to determining damage based on changes in mechanical properties, as well as the requirements for functions that can be used to describe experimental dependencies. The considered models have been classified according to the characteristic form of their mathematical function: polynomial, power, exponential, logarithmic, and trigonometric models. A distinct category has been established for models utilizing cumulative distribution functions. The possibilities for further development and application of phenomenological models of residual mechanical properties for the improvement of strength analysis approaches for composite structures have been outlined.

5:08

S77:E09 Apr 21, 2026

Microstructure, tensile and fractographic behavior of friction stir welded joints AA6061 and AA2024

https://doi.org/10.3221/IGF-ESIS.77.09 The present study focused on the evaluation of critical influencing parameters of the FSW of AA6061-T6 and AA2024-T351 alloys. The materials properties of AA6061-T6 are heat-treatable alloys possessing properties of good resistance to corrosion, and AA 2024-T351 has superior strength, which is very important in load bearing section. The joining of these AA alloys will result in excellent mechanical qualities. Friction stir welding (FSW) is a very crucial joining method in the aerospace and automobile sector resolving most of the problems connected to the requirement of high-performance welded joints. In preference, this kind of joining has more advantages over common joining processes, such as less defects, no use of consumable electrodes, and it can be applicable in welding at any position. In this research, optimization of critical influencing input parameters was conducted using the L9 orthogonal array by the Taguchi method. Overall, there were 9 experimental trials after designing in the statistical software. The input process parameters selected for optimization are tool rotation speed (TRS), welding feed rate (WS) and tilt angle, which is maintained constant at zero degrees. The relative contribution percentages of the input variables to the optimized outputs (TRS and WS) were determined via ANOVA.

5:12

S77:E08 Apr 17, 2026

Experimental and numerical investigations of lattice structures

https://doi.org/10.3221/IGF-ESIS.77.08 The present work investigates the compressive mechanical response of three lattice structures manufactured via VAT photopolymerization. A bio-inspired architecture, derived from the observation of Euplectella aspergillum, was compared with square and triangular lattice configurations. Experimental uniaxial compression tests and multi-step nonlinear finite element analyses were carried out for each topology to highlight differences in their mechanical behaviour. The results demonstrate that the bio-inspired structure exhibits superior mechanical performance compared to conventional square and triangular geometries. Furthermore, the proposed simulation methodology proved effective for design purposes, enabling the consideration of instability phenomena and contributing to safer structural design. Finally, micromechanical modelling was employed to link the micro-architecture to the effective macroscopic properties. In particular, a micro-mechanical model allowed to predict the elastic moduli and yield strength, highlighting a stretch-dominated behaviour in elastic regime.

4:23

S77:E07 Apr 16, 2026

Mechanical and tomographic characterisation of recycled Carbon Fibre Reinforced Polymer (rCFRP) using a fully mechanical environ

https://doi.org/10.3221/IGF-ESIS.77.07 The widespread use of carbon fibre-reinforced polymer (CFRP) composites in sectors such as aerospace and aviation calls for the adoption of sustainable recycling protocols. This research evaluates the mechanical and tomographic characterisation of recycled CFRP obtained via an innovative fully mechanical sustainable process. Thin (0.8 mm) and thick (2.0 mm) recycled non-woven fabric fibre laminates were subjected to uniaxial tensile testing in accordance with ASTM D3039M. The results revealed that the thick laminates achieved an UTS of 310-330 MPa and a Young’s modulus of 21.3–21.7 GPa in longitudinal direction, whilst the transverse properties were significantly lower. Despite the excellent cleanliness of the fibres, the mechanical performance of the composite laminates remains limited. Fractographic analysis using scanning electron microscopy (SEM) and internal volumetric evaluation using X-ray micro-tomography revealed severe spatial inhomogeneity in the distribution of the recycled fibres. Dense fibre bundles impeded the microscopic capillary infiltration of the resin, generating critical volumetric porosity and jagged shrinkage voids that act as severe stress concentrators. Consequently, it is essential to optimise the spatial uniformity within the mat of recycled precursors in order to reduce internal defects and fully exploit the structural potential of mechanically recycled CFRP.

5:30

S77:E06 Apr 14, 2026

Application-driven optimization of Ti-6Al-4V alloy via customized heat treatments

https://doi.org/10.3221/IGF-ESIS.77.06 This paper examines the influence of controlled heat treatments on the mechanical behaviour of Ti-6Al-4V (Grade 5 Titanium alloy) to improve its performance in structural and high performance applications. Ti-6Al-4V is widely used in aerospace, biomedical and automotive components because of its high strength-to-weight ratio and corrosion resistance: however, simultaneously optimizing strength, ductility, fracture toughness and fatigue resistance remains challenging. Because the alloy is highly sensitive to thermo-mechanical history, heat treatment provides an effective means of tailoring its mechanical response. Four microstructural conditions were examined: (i) annealed, A, (ii) solution-treated and aged, STA, (iii) β-annealed, BA, and (iv) β-solution-treated and overaged, BSTOA. Optical and scanning electron microscopy were used to characterize the resulting microstructures and tensile, hardness, impact strength, fracture mechanics and fatigue tests to determine the respective mechanical properties. A condition exhibited the highest ductility, whereas the STA treatment produced the greatest strength and hardness; BA condition improved fracture toughness, while BSTOA treatment provided the highest high cycle fatigue limit. These findings demonstrated that appropriate selection of the thermal treatment process can significantly enhance the mechanical performance of Grade 5 Titanium alloy for advanced engineering applications.

5:31

S77:E05 Apr 5, 2026

Effect of corrosion damage on the fatigue behavior of S460NL High-Strength Steel under cyclic loading

https://doi.org/10.3221/IGF-ESIS.77.05 The present study investigates the influence of corrosion exposure on the fatigue behavior of S460NL high-strength structural steel, a material that is frequently utilized in offshore and civil engineering structures. Accelerated corrosion was simulated under controlled laboratory conditions for exposure periods of 3 days, 6 days, and 6 + 3 days, in addition to specimens subjected to natural atmospheric corrosion. To this end, fatigue tests were performed to obtain S–N curves, and the results were evaluated using Basquin’s law and the probabilistic Castillo–Canteli model. The findings indicate that corrosion has a substantial impact on fatigue resistance. The endurance limit exhibited a decline from 214 MPa for the reference specimens to 176 MPa following three days of corrosion, 135 MPa after six days, and approximately 92 MPa after combined corrosion exposure, signifying a reduction of up to 57%. Fractographic observations revealed that corrosion pits act as stress concentrators, thereby promoting early crack initiation. A discernible correlation was identified between corrosion mass loss and normalized endurance limit. These findings highlight the importance of considering corrosion effects in fatigue life assessment and structural design of high-strength steel components.

5:14

S77:E04 Apr 4, 2026

On the relationship between crack initiation angle and loading equivalent angle for asymmetric ...

https://doi.org/10.3221/IGF-ESIS.77.04 In this work, the prediction of crack initiation angle (θo) under mixed mode (I/II) load is estimated from the generalized minimum plastic zone radius (GMPZR) criterion. The paper presents a detailed study on the crack-tip plastic core for asymmetric three-point bend (TPB) specimens of different crack-to-width (a/W) = 0.4-0.7 ratios and loading equivalent angle (βeq) using elastic finite element (FE) analyses. The θo estimated from the FE analysis is compared with the GMPZR criterion, other fracture criteria, and available experimental results. It is found that the θo evaluated from the FE analysis provides the best correlation with the GMPZR criterion among other fracture criteria. The FE results are used to propose an analytical relation between θo and βeq. This proposed relationship can be used to quickly estimate the crack initiation direction/angle for TPB specimens with only βeq available. Finally, the effect of T-stress on θo, will be assessed using as estimated from the GMPZR criterion.

5:28

S77:E03 Apr 3, 2026

Effect of specimen size and type on real-mode-I fracture toughness of hooked-end steel fiber-reinforced concrete

https://doi.org/10.3221/IGF-ESIS.77.03 This paper studied the effects of specimen size and type on the real-mode-I fracture toughness (KIC )of steel fiber-reinforced concrete (SFRC) specimens. Mode I KIC tests were performed using semicircular bend (SCB) and center-cracked circular disk (CCCD) specimens with different sizes and crack-to-depth ratios, (a/R). SCB Specimens were tested under three-point bending, and CCCD specimens were tested under indirect tension test conditions to achieve pure Mode I crack growth. Moreover, KIC was analyzed as a function of specimen type (SCB and CCCD), specimen size (R values of 50, 75, 100, and 125 mm), and a/R ratios of 0.2, 0.3, 0.4, and 0.5. The results clearly show that the KIC of SFRC exhibits a distinct size effect: it increases with specimen radius up to a critical range of 75-100 mm, after which it levels off. The a/R ratio is an important parameter affecting the toughness; higher values of a/R result in increased KIC values, with increases of 12.9% for CCCD specimens and 22.7% for SCB specimens when a/R is raised from 0.2 to 0.5 at R=75 mm. In addition, the failure mode shifts from ductile fiber pull-out at shallow a/R to brittle fiber rupture at highera/R. The results also emphasize the importance of using geometry-adjusted models, such as Bazant’s size effect law (SEL), especially when dealing with SFRC, since fiber distribution and crack-bridging efficiency depend on both size and geometry.

5:34

S77:E02 Apr 3, 2026

Effect of continuous carbon fiber layup architecture on tensile performance of hybrid FDM composites

https://doi.org/10.3221/IGF-ESIS.77.02 Hybrid continuous fiber–reinforced composites produced by fused deposition modeling (FDM) offer a promising solution for lightweight load-bearing structures. However, their mechanical performance is strongly governed by internal reinforcement architecture. This study experimentally investigates the effect of continuous carbon fiber layup orientation on the tensile behavior of hybrid FDM composites based on three short-fiber-reinforced thermoplastic matrices: ABS, PA12, and PET-G. Specimens were fabricated using continuous fiber co-extrusion technology with controlled constant and combined fiber layup schemes. Uniaxial tensile tests with non-contact strain measurement were performed to evaluate Young’s modulus, ultimate tensile strength, and strain-to-failure. Results show that fiber alignment with the load direction is essential for maximizing stiffness and strength, while the polymer matrix primarily controls ductility and failure strain. Combined layups with axially oriented and off-axis layers offer a balance between strength and damage tolerance. Fractographic observations indicate mixed Mode I/Mode II failure governed by structural anisotropy and matrix plasticity. These findings establish the design basics for optimizing hybrid continuous-fiber-reinforced FDM composites and provide a practical framework for the development of additively manufactured structural components.

5:20

S77:E01 Apr 3, 2026

Multimodal residual stress evaluation following one-sided dimpling in a Ti-6Al-4V alloy plate

https://doi.org/10.3221/IGF-ESIS.77.01 Residual stress significantly influences the mechanical performance, fatigue resistance, and structural reliability of titanium alloys used in engineering applications. This study investigates the residual stress distribution induced by one-sided dimpling in Ti-6Al-4V alloy using a combined experimental–numerical approach. Localized plastic deformation produced by spherical indentation generates stress fields that are difficult to characterize with a single technique. Residual stresses in the plane were evaluated using Focused Ion Beam–Digital Image Correlation (FIB-DIC) and Electronic Speckle Pattern Interferometry (ESPI). To evaluate the residual stress through the sample thickness, the cross-section warp method was used, that analyze the warping (deplanation) of the cross-section after cutting and provides an alternative way to infer the internal stress distributions and complements existing measurement techniques. The results reveal compressive residual stresses near the dimpled surface and tensile stresses developing at greater depths due to elastic recovery and equilibrium constraints. Finite element simulations match the experimentally observed stress distributions and confirm the reliability of the proposed methodology. The validated finite element model provides a predictive framework for future studies, enabling systematic analysis of how indentation depth and the indenter diameter affect the magnitude and distribution of compressive residual stresses, and supporting the optimization of dimpling parameters for improved structural performance.