A novel specimen geometry for an improved estimation of hydrogen effects on the tensile behavior of face-centered cubic alloys

Effect of specimen geometry on the dynamic direct tensile responses of ultra-high-performance fiber-reinforced concrete

Accurate characterization of the out-of-plane shear properties of laminated composites is essential for understanding their structural integrity under complex loading. While in-plane shear moduli are well-studied, out-of-plane properties are often challenging to measure, especially in natural fiber-based laminates. This study proposes an experimental method, based on the Mindlin-Reissner plate theory, to determine out-of-plane shear moduli of woven kenaf laminates using a torsional test setup enhanced by three-dimensional digital image correlation (3D-DIC). Rectangular specimens of two lengths (50 mm and 90 mm) were clamped and subjected to quasi-static torsion. The torque was recorded using a load cell, and full-field strain was captured via 3D-DIC. The average in-plane shear modulus (G 1 2) was found to be 1589.5 MPa, while the out-of-plane shear modulus (G 1 3) was 693.85 MPa. A specimen geometry sensitivity analysis revealed that a width-to-thickness ratio below 3 leads to significant overestimation or underestimation of the respective shear moduli. The proposed method is non-destructive, adaptable to relatively thin laminates, and well-suited for characterizing sustainable composites, making it a promising tool for design and performance assessment in bio-based structural applications.

This study evaluates Edge-Focused Wire Arc Additive Manufacturing (EF-WAAM) for CT38 steel using an ER70S-6 filler. EF-WAAM employs an edge-guided toolpath with a prescribed travel angle to localize heat input per unit length, narrow the heat-affected zone, and mitigate residual stress relative to conventional WAAM. Under standardized 3-point bending with identical specimen geometry and span, the maximum flexural stress of EF-WAAM builds ranges from 2,414.21 to 3,338.11 MPa (n = 5 per condition). The best case improves 171% over the CT38 substrate (1,231.5 MPa) and exceeds typical values for conventional WAAM (< 2,000 MPa). Mass efficiency, reported as strength-to-density (σ/ρ), reaches 420.4 MPa·cm³·g ⁻ ¹, representing gains of 40.4% versus the substrate and 83.3% versus conventional WAAM. An artificial neural network (ANN) maps process variables—current, step-over distance, travel angle, travel speed, layer thickness, and strain—to stress and reconstructs full stress–strain curves with high agreement on training, validation, and held-out test sets. ANOVA/S-N and sensitivity analyses indicate layer thickness is the dominant factor within the explored window, with beneficial interactions from travel speed and current that moderate thermal gradients. The study also demonstrates the feasibility of internal features (e.g., 3D spiral channels) while maintaining controlled thermal fields. Overall, EF-WAAM delivers higher flexural strength and improved mass-specific performance within a standardized, reusable evaluation pipeline, offering a transferable workflow for other WAAM variants. Beyond a single case, we provide a reusable evaluation pipeline, actionable parameter windows, and cross-variant metrics (σ/ρ, AER) together with an ANN routine that reconstructs full stress–strain curves from process vectors. These assets enable practitioners to transfer the method to related WAAM variants without additional sensing or bespoke hardware.

Experimental and numerical investigation of shear-driven fracture in hybrid tape/fabric-laminate end-loaded-split specimens

ABSTRACT Predicting the ageing behaviour of adhesively bonded joints is a key challenge in adhesive bonding technology and is essential for their broader use in steel construction. This paper presents a method for predicting the long-term performance of thick-layer adhesive bonds under hygro-thermo-mechanical (htm) stress. This approach is based on experimental investigations into the water absorption of the adhesive, which is recorded gravimetrically and described using Fickian´s diffusion model. Different temperature and humidity influences on the diffusion parameters are considered using an Arrhenius approach. The mechanical behaviour is analysed by means of quasi-static tests and systematic creep experiments different specimen geometries. Numerical modelling is based on an adhesive layer equivalent model that represents the linear viscoelastic behaviour and damage resulting from htm loading. Temperature and humidity influences are recorded via a time-temperature-water concentration shift, and the multi-axial nature of the failure is described via a comparative stress. Validation is performed using component-like specimens and transient FE simulations with LS-DYNA, which utilise the coupling of diffusion and heat conduction problems. The case study shows that the developed concept enables a reliable life prediction and thus contributes significantly to confidence in adhesive bonding technology.

This study presents a comprehensive investigation into the dynamic compressive behavior of ten distinct rock types using a Split Hopkinson Pressure Bar system. The selected rocks represent igneous, sedimentary, and metamorphic origins and are sourced from six geotechnically significant sites across India, each designated as a project of national importance. To establish the fundamental characteristics of the materials, an extensive series of petrological, physical, and static mechanical tests were first conducted. Cylindrical specimens of varying sizes were subsequently prepared to evaluate the influence of strain rate and specimen geometry on dynamic response parameters, including peak compressive strength, dynamic elastic modulus, and peak strain. The experimental data analysis reveals significant variations in mechanical response as a function of rock type and specimen dimensions under high strain-rate loading. A nonlinear regression model is proposed to correlate elastic parameters obtained under static and dynamic loading conditions. Furthermore, the study demonstrates the practical applicability of dynamic test results in estimating rock mass properties. To enhance engineering relevance, all rocks are systematically classified using the Deere-Miller rock mass rating scheme under both static and dynamic loading scenarios. The results contribute valuable insights for the design and analysis of rock structures subjected to dynamic loads such as blasting and seismic events.

Abstract The increasing demand for durable infrastructure has intensified interest in understanding concrete behavior under dynamic loading, particularly fatigue. Although temperature changes have limited influence on concrete’s ultimate strength, they can substantially affect fatigue performance by accelerating microstructural degradation. A notable but insufficiently characterized phenomenon in this context is self-heating, an internal temperature rise observed during cyclic loading. This study examines self-heating in concrete through transient thermal finite element simulations performed on five specimen geometries commonly employed in compressive fatigue tests. The model decouples the mechanical effects, incorporating viscoelastic energy dissipation as the internal heat source. Complementary complex modulus (quasi-static) and tensile fatigue tests were conducted on saturated and dry concrete specimens to provide indirect support for the modelling approach. The simulations reproduced trends reported in literature, including higher temperatures at the specimen core. Simulations revealed that specimen geometry – particularly diameter – was found to strongly govern the thermal response. Saturation increased the complex modulus but had minimal effect on fatigue life. Overall, the numerical results are consistent with the hypothesis that viscoelastic dissipation contributes to self-heating, even if the resulting temperature rise is very small (order of 10 − 4 °C) under tensile fatigue conditions. The agreement between simulations and experiments reinforces that even small viscoelastic effects may contribute to temperature rise under cyclic loading. These findings highlight the importance of considering thermal effects in fatigue analyses and suggest that incorporating viscoelastic mechanisms may improve the representation of heat generation in concrete subjected to cyclic loading, improving durability assessments of concrete structures.

Accurate thermal characterization of building insulation materials is essential for reliable energy performance assessment, regulatory compliance, and the development of high-performance envelopes. On one hand, the growing adoption of innovative insulating products, such as nanoporous materials, aerogel-based composites, bio-based panels, and thin insulating coatings, helps to enhance buildings’ energy efficiency by means of sustainable raw materials. On the other hand, conventional measurement techniques encounter significant challenges, due to their heterogeneity, reduced thickness, and unconventional geometries. In this study, an intra-laboratory comparison of three widely used methods for thermal conductivity determination is presented: the Transient Plane Source (TPS, Hot Disk) method, the Guarded Hot Plate (GHP) method, and the Heat Flow Meter (HFM) method. A total of twelve insulating materials, spanning super-insulating cores, insulating renders, bio-based panels, and nanocomposite coatings, were experimentally characterized under controlled laboratory conditions. A view on the analyzed insulating materials’ cradle-to-grave environmental impact is also given, to enhance the users’ awareness for the highly informed choice. The results highlight systematic differences between transient and steady-state approaches, with TPS measurements generally exhibiting larger deviations for materials characterized by surface roughness, limited thickness, or strong internal heterogeneity. In contrast, GHP and HFM methods show closer agreement when specimen geometry and stabilization requirements are satisfied. The influence of contact resistance, probing depth, specimen preparation, and uncertainty propagation is critically analyzed for each technique. The study provides practical insights into the applicability limits of commonly used thermal characterization methods and emphasizes the importance of selecting measurement techniques in relation to material morphology and testing constraints. These findings support more reliable thermal property assessment of emerging insulation materials and contribute to improved consistency between laboratory measurements and energy performance evaluations for buildings.

Metal mesh reflective surfaces are widely used in deployable antennas mounted on satellites where lightweight and stowability are required; however, quantitative characterization of reflective performance is difficult due to complex woven/knitted structures. This paper presents a modeling method that characterizes the reflection coefficient of complex mesh fabrics by combining a per-band effective wire radius reff estimation procedure with the Casey surface impedance model. The lattice spacing is fixed from the specimen geometry, the electrical conductivity is set to the material property of gold (σ = 45.2 MS/m), and reff is determined as a single parameter that minimizes the error against the measured reflection coefficient in each frequency band. For validation, waveguide-contact measurements were performed on three Atlas-series mesh specimens fabricated with gold-coated molybdenum wire (diameter: 30 μm), measuring each specimen across all three waveguide standards (WR-340, WR-90, WR-28) with nine repeated trials per configuration, totaling 162 measurement runs. The estimated reff ranged from 10.1 to 44.5 μm depending on band and polarization, with RMSE below 0.021 dB in all native-band fits. Even for the same specimen, directional reff values differed by up to 1.78× due to the anisotropy of the weave structure, confirming that polarization dependence must be considered in mesh reflector antenna design.

Cold forging and sheet‑metal bulk forming operations typically involve severe deformation, high contact pressures, and substantial surface enlargement. As highlighted in previous studies, friction behavior under these extreme conditions is governed by temperature, contact pressure, sliding velocity, and changes in the real contact area due to surface expansion. This work presents a newly developed linear sliding tribotester designed to characterize the friction response of metal sheets subjected to sheet‑metal bulk forming conditions. The testing procedure consists of two stages. In the first stage, the sample is compressed to intentionally modify and enlarge the initial contact surface, with the degree of surface expansion controlled by the specimen geometry. In the second stage, once the surface has been altered, frictional contact is generated between the sample and a sliding table, enabling the measurement of normal and tangential forces. These force measurements are subsequently used to determine the mean coefficient of friction. The results obtained constitute the first dataset toward the development of a multi‑scale friction model for sheet‑metal bulk gear forging. This model aims to incorporate the effects of extreme contact pressures, asperity flattening, and lubricant-related hydrostatic and hydrodynamic mechanisms.

Accurate determination of the elastic parameters of expanded polystyrene (EPS) in the small-strain range is essential for its structural applications. This study investigates the compression modulus of elasticity and Poisson's ratio of EPS with a nominal density of 20 kg/m3 through unconfined compression tests on cubic specimens of 50, 100, 200 and 300 mm side length and rectangular 50 × 50 × 100 mm specimens. Three deformation measurement methods were compared: video extensometer (VE) and crosshead displacement measurements performed at two independent laboratories. Two moduli of elasticity, E0-0.5 and E0.5-1.0, were determined within vertical strain (εv) ranges of 0-0.5% and 0.5-1.0%, respectively. VE-based moduli were up to twice the values obtained from crosshead displacement measurements, demonstrating that global deformation measurements significantly underestimate material stiffness in the small-strain range due to bedding error. The stress-strain relationship within εv ≤ 1%, commonly regarded as the elastic range of EPS, was found to be clearly nonlinear and is well described by a bilinear model. No size effect on moduli was observed in VE measurements, while crosshead displacement measurements showed increasing moduli with specimen height, stabilising at 100 mm and above. VE-based Poisson's ratio v0-0.5 was 0.23 for cubic specimens and 0.09 for rectangular specimens, suggesting a significant effect of specimen geometry. The results highlight the importance of local strain measurement for accurate characterisation of EPS elastic behaviour, particularly in structural applications.

Synthetic S–N curves for sintered steels based on density, hardness, and local stress parameters: A data analysis

Ensuring the safe repurposing of X70 pipelines for hydrogen transport requires understanding how hydrogen interacts with deformation and local stress state. Two specimen geometries—a standard miniature tensile specimen and one with a hole at the gauge centre—are evaluated under in-situ electrochemical hydrogen charging. The effects of current density, pre-strain, and high stress triaxiality (η ≈ 0.48) are systematically examined. Increasing hydrogen flux reduces ductility sharply, whereas yield strength remains nearly unchanged. Pre-strained specimens exhibit higher embrittlement due to enhanced hydrogen trapping, and stress-concentrated specimens exhibit the most severe loss of plasticity and brittle fracture. Fractographic and cross-sectional observations reveal hydrogen-assisted cracks at surface for higher hydrogen fugacity and a transition from ductile to quasi-cleavage fracture. Under similar saturated hydrogen concentration, these results demonstrate that hydrogen fugacity, plastic deformation, and local stress state act synergistically to control embrittlement severity in X70 pipeline steels exposed to hydrogen environment. • In-situ tensile testing reveals hydrogen-induced ductility loss in X70 steel. • Pre-strain accelerates embrittlement through enhanced hydrogen trapping. • Stress triaxiality (η ≈ 0.48) amplifies hydrogen-assisted brittle fracture. • Surface hydrogen-assisted cracks observed like gaseous hydrogen testing. • Embrittlement severity is governed by hydrogen fugacity and local constraint.

Pervious concrete (PC) is a sustainable solution for mitigating urban drainage and surface runoff; however, casting and compaction parameters, specimen geometry and standardised testing methods remain insufficiently defined, limiting consistent performance evaluation. This study examines, for a single PC mix, the influence of specimen geometry and moulding technique on mechanical properties and permeability, compares technical standards and evaluates the feasibility of standardisation. The adapted infiltration test for cubic specimens proved effective and simpler than testing larger blocks. Results showed that permeability increased as specimen height decreased under single-layer roller compaction, indicating dimensional dependence. For compressive strength, 100 mm cubes exhibited lower variability (CV ≈ 7.4%) than 150 mm cubes (CV ≈ 14.8%) and cores (CV = 19.1%). The four-point flexural test provided more reliable elastic modulus values and enabled the reuse of prisms for splitting tests. Overall, the results support simplified, standardised PC testing protocols with reduced time and resource demands while maintaining data consistency.

This study presents a distribution-optimized mesostructure estimation method for statistically modeling near-surface aggregate size distributions in concrete by optimizing the spatial arrangement of polydisperse spherical aggregates with respect to formwork boundaries. The approach is based on minimizing the deviation between a generated cumulative aggregate volume function and an idealized linear target function corresponding to a constant area fraction along the specimen depth. To enable efficient computation for systems containing a large number of aggregates, grain size groups derived from the grading curve are represented using symmetric Beta distributions, allowing each group to be described by a single shape parameter. The resulting optimization problem is solved using a derivative-free Powell algorithm. The method inherently captures wall effects, leading to a migration of smaller aggregates toward the specimen boundaries to compensate for the geometric constraints of bigger aggregates. Experimental validation was performed for a single concrete mixture and specimen geometry by determining the depth-dependent mean bulk density of a concrete cube using incremental surface grinding combined with high-resolution 3D laser scanning. The optimized mesostructure shows strong agreement with measured density profiles for the investigated specimen. While the validation is limited to a single mixture and geometry, the results indicate that the proposed method is a computationally efficient approach for incorporating wall effects into mesoscale concrete models. Furthermore, increasing aggregate volume fractions intensify the near-surface accumulation of fine particles.

Rotary press forging (RPF) has been introduced in the last century. Despite its advantages, it produces defects in the forgings such as mushrooming, eccentricity, and twisting. Rotary hammer forging (RHF) is a new process invented by the author to reduce such defects. RHF is considered as a multi-axes compression forging process where the material is subjected to several repeated hammering blows to be deformed incrementally and partially, while the produced deformation zone is swept over the whole area of the workpiece. Previous works showed that the specimen geometry, the inclination angle and the rotational speed affect such defects as mushrooming effect, eccentricity and twisting angle, but they are less severe in RHF than RPF. The present work has studied the effect of the forming degree (FD) on the forgings produced by both RPF and RHF to compare between the two processes. Special set-ups have been used where a die is rotating while either a pressing head or hammering head is used to deform the specimen. Independent variable parameters were chosen such that the specimen geometry H/D = 1, the inclination angle = 4[Formula: see text], the rotational speed N =260 rpm, number of blows per revolution in case of RHF = 1.2. The results showed that FD has its influence on the mushrooming effect, twisting angle, and eccentricity, although they are less in the case of RHF. RHF reduces the defects referred to RPF by 5 to 13% for the mushrooming effect, 0 to 33% for the eccentricity, and 70 to 80% for the twisting angle. Thus, RHF is advantageous than RPF.

This experimental study explores the behaviour of columns with double-skinned solid core concrete-filled steel tubular (DS-CFST) sections. Many experimental studies have been conducted on double-skinned hollow CFST sections so far, and this research has involved evaluating the performance of various configurations of steel tube geometry (square and circular combinations) of solid-core CFST specimens. Eight CFST short columns were subjected to axial compression, each measuring 410 mm in height (H). The study investigated the effects of various parameters, including concrete strength, steel area, width-to-thickness ratio, steel and concrete core percentage, and inner steel embedment position, on CFST short columns with slenderness ratios (λ) ranging from 9.4 to 10.9. The test results showed improvements in DS-CFST column axial compression, ductility, stiffness, failure modes, and structural behaviour due to adequate steel inner tube embedment. The CFSC specimens exhibited 6.64 times higher results than the steel tubes and 2.33 times greater strength than the CFST specimens, while other steel tube embedded specimens demonstrated significant strength improvements. The results are checked with the current codal provisions, ANSI/AISC-360, EC-4 and modelled by an artificial neural network (ANN).

Multimaterial additive manufacturing offers the potential to create functionally graded components from highly filled photocurable particle-reinforced composites (PRCs). While prior research has focused on 3D printing photocurable slurries with high volume loadings, the mechanical properties of multimaterial interfaces have not been measured. Furthermore, the effects of spatially varying photocuring on highly filled PRCs have not been quantified. To address these issues, this study isolated the effects of 3D-printed multi-extrusion and multimaterial coplanar interfaces on the ultimate tensile strengths (UTSs) for two glass-reinforced photocurable formulations under different processing conditions. Tensile specimens were manufactured via casting and vibration-assisted printing, and their UTSs and bulk porosities were measured. Multiple materials at the interface had a negligible effect on the rupture location compared to discontinuities in the print toolpath. Furthermore, the contributors to UTSs in descending order of importance were altered slurry composition and decreased porosity from vacuum processing, stress concentrations from tensile specimen geometry, and nonuniform photocuring. Understanding the effects of the material and processing conditions on the interface is important when designing high-performance, functionally graded PRCs for aerospace applications, for which this study lays the groundwork.

The uniaxial tensile test is a common and fundamental test in materials science and engineering, in which a specimen is subjected to controlled tension until failure. From this, the stress-strain curve and many property parameters of the material can be calculated, such as tensile strength, ultimate strength, maximum elongation, Young's modulus, Poisson's ratio, and yield strength. As fibrous materials, such as paper and paperboard, become more popular, accurately measuring their mechanical properties becomes essential for developing and applying these materials, especially in packaging. However, since they are anisotropic and inherently inhomogeneous due to the arrangement of the fibers, accurately determining their mechanical properties is not straightforward. This study investigated how several key factors influence the results of tensile tests on fiber-based materials: sample size and deformation measurement techniques using three fiber materials. This study also compared three different strain recording methods: digital image correlation (DIC), video extensometer, and conventional extensometer (Traverse). The DIC technique emphasized the effect of the inherent inhomogeneity of the paperboard on the overall mechanical properties obtained from tensile tests. The results indicated that sample size has a negligible effect on the stress-strain curve, and any apparent influence likely stems from slip at the grips during tensile testing. However, sample size does affect paperboard fracture to some extent. The study also provided recommendations for optimal specimen geometry and deformation recording methods to improve the accuracy and repeatability of tensile testing of fiber-based materials.