Search Results (189)

Short fibre-reinforced polymers (SFRPs) are increasingly used in structural applications where mechanical integrity under complex loading is critical. However, conventional modelling approaches often fail to accurately predict mechanical behaviour in weldline regions formed during injection moulding, where microstructural anomalies and pre-existing damage significantly degrade performance. This study addresses these limitations by extending a hybrid micro–macromechanical constitutive framework to incorporate localised initial damage at weldlines. Calibration and validation of the model were conducted using directional tensile tests on dumbbell-shaped polyamide 66 specimens reinforced with 25 wt% glass fibres, featuring controlled weldline geometry. Digital image correlation (DIC) was employed to capture strain fields, while injection moulding simulations provided fibre orientation distributions and weldline positioning. Results demonstrate that incorporating initial damage and its independent evolution for the cold weld region significantly improves prediction accuracy in weldline zones without compromising model efficiency. The proposed approach can be integrated seamlessly with existing finite element framework and offers a robust solution for simulating SFRP components with weldlines, enhancing reliability in safety-critical applications. Full article

In the absence of standard procedures for testing 3D-printed soft polymers, an experimental protocol was proposed to assess the suitability of Flexible 80A Resin for a pediatric trachea anatomical 3D model for surgical simulation. Eighteen specimens printed via stereolithography are involved, including anatomical, cylindrical, and dog-bone shapes, to investigate the geometry effect on measured properties. Static tensile tests revealed that using standardized dog-bone specimens as a reference for the material’s Young’s modulus leads to a mean absolute percentage error (MAPE) up to 50% compared to anatomical specimens. Measurement uncertainty combined repeatability with input errors, and the ANOVA test confirmed the need for dedicated mechanical measurements when evaluating complex 3D-printed geometries. The study concludes the suitability of selected material: the average elastic modulus of anatomical specimens was 4.75 MPa, closely matching values reported for tracheal tissue in the literature, with a MAPE of only 2%. Dynamic mechanical tests showed trachea-like viscoelasticity: anatomical specimens were consistently stiffer and more dissipative than cylindrical ones. Creep tests confirmed the viscoelastic behavior simulating airway time scales. The anatomical specimens exhibit faster local relaxation, while cylindrical ones show slower long-term relaxation, both modeled by a two-element generalized Maxwell model (R² = 0.99 and 0.98). Full article

Different combinations of round and flat tensile specimens for different gripping systems of Austempered Ductile Irons (ADIs) were produced from the same 25 mm Y-block castings to investigate the effect of the specimen geometry and gripping system on the tensile mechanical properties of ADIs. Particular attention was paid to the analysis of strain-hardening behavior of ADIs that can be related to the stability of ausferrite, when austenite transforms into martensite. Moreover, Digital Image Correlation (DIC) was carried out on the flat tensile specimens to analyze the strain distribution of the material in real time. To quantify the austenite stability with plastic deformation, X-ray Diffraction (XRD) analysis was performed on ADIs before and after straining. Finally, Finite Element Modeling (FEM) simulations were carried out to analyze the stress distribution along the tensile specimens in all the different tensile testing configurations (tensile specimen geometry + gripping system). The flat specimens showed lower ductility and higher strain-hardening rates; however, the flat tensile specimens with the wedge gripping system experienced the highest strain-hardening rate, suggesting a significant decrease in the ausferrite stability in this tensile testing configuration. FEM simulations showed that the specimen geometry and the gripping system influenced the tensile behavior of ADI by reducing the ductility because of stress intensification and triaxiality effects. Furthermore, the stress intensification and triaxiality factor caused a higher strain-hardening rate, which was associated with increased ausferrite instability. Full article

Laser powder bed fusion (L-PBF) enables the fabrication of complex lattice-type structures composed of thin struts, offering lightweight, high-strength advantages in aerospace and biomedical applications, among others. While extensive research has examined full lattices and process parameter effects individually, the combined influence of strut geometry, configuration, and processing conditions on mechanical properties remains less understood. This study investigates how the strut number, strut size, cross-sectional shape, and laser energy input affect the mechanical properties of thin-strut L-PBF tensile specimens. Ti-6Al-4V struts were designed and fabricated using an EOS M270 system using five linear energy density (LED) levels. The fabricated specimens were measured in porosity using micro-scaled computed tomography and further evaluated using a tensile tester. The results showed that increasing the strut number leads to significant reductions in tensile strength, even with the same overall cross-sectional area, especially at low LED levels. Size effects on mechanical strengths were observed, though mostly minimal, except at the smallest strut size, where defects tend to be more critical. Circular and square shapes performed similarly under general LED conditions; however, square struts exhibited inferior behavior at the lowest LED level. Overall, LED is the most influential factor, with the greatest tensile strength occurring near 0.2 J/mm; further decreasing or increasing the LED both increase the porosity, degrading mechanical strengths. Full article

Additive manufacturing (AM) via selective laser melting (SLM) is increasingly deployed in aerospace, biomedical, and tooling applications where complex geometries and high performance are required. Yet, process-induced anisotropy and microstructural heterogeneity can strongly affect mechanical and tribological behavior. This study systematically evaluates the combined effects of build orientation (0°, 45°, and 90° relative to the build plate) and post-build heat treatment (as-built, 600 °C, and 860 °C) on the phase constitution, microstructure, hardness, tensile response, and dry sliding wear of SLM-fabricated 316L stainless steel. X-ray diffraction indicated a fully austenitic (γ-fcc) structure without detectable secondary phases across all conditions. Orientation-dependent substructures were observed: ~1 µm equiaxed cellular features at 0°, finer 0.3–0.5 µm cells at 45°, and 1–2 µm elongated features at 90°. Microhardness varied with orientation; relative to 0°, 45° specimens were ~15 HV higher, whereas 90° specimens were ~10 HV lower. Heat treatment at 600 °C promoted refinement and recovery of the cellular network, most pronounced in the 45° orientation, while treatment at 860 °C largely erased melt pool boundary contrast, producing a more homogeneous particle-like microstructure. Tensile fractography revealed dimpled rupture in all cases; the 90° orientation showed finer dimples and lower hardness, consistent with a ductile failure mode under reduced constraint. Dry sliding wear tests identified adhesive wear, intensified by the build-up of transferred fragments, as the dominant mechanism in both as-built and 600 °C conditions. Changes to melt pool morphology after 860 °C heat treatment correlated with altered wear track widths, with the 0° condition showing a notable narrowing relative to the 600 °C state. These results highlight processing pathways for tailoring anisotropy, strength–ductility balance, and wear resistance in SLM 316L. Full article

This study evaluates the influence of fiber type, geometry, and interfacial behavior on the physical and mechanical performance of cementitious composites reinforced with recycled pulp from beverage cartons (RPBC), bamboo fiber (BF), and eucalyptus fiber (EF) as the sole reinforcing agents. The BF was rounded in shape and had the highest aspect ratio, while the ribbon-shaped EF exhibited the highest tensile strength index. The RPBC fibers were fibrillated and the shortest, with a ribbon shape. Flexural strength results showed that RPBCC achieved a maximum strength that was 47.6% higher than the control specimen (0% fiber), outperforming both BF- and EF-reinforced counterparts. This superior performance is attributed to the higher fibrillation level of the ribbon-shaped RPBC fibers, which promoted better fiber–matrix bonding. As the fiber content increased, the bulk density of EFC and BFC decreased linearly, while RPBC composites showed only a modest decrease in density. Porosity steadily increased in EFC and BFC, whereas a non-linear trend was observed in RPBCC, likely due to its unique morphology and fibrillation. Conversely, EFC exhibited significantly higher maximum fracture toughness (3600 J/m² at 10 wt.%) compared to PBFCC (1600 J/m² at 14 wt.%) and BFC (1400 J/m² at 14 wt.%). This enhancement is attributed to extensive fiber pullout mechanisms and increased energy absorption during crack propagation. Overall, all composite types demonstrated flexural strength values above 4 MPa, placing them in the Grade I category. Those reinforced with 10–14% RPBC exhibited strengths of 11–12 MPa, categorizing them as Grade II according to ASTM C1186-02. Full article

Laser beam powder bed fusion of metals (PBF-LB/M, or simply L-PBF) has emerged as one of the most competitive additive manufacturing technologies for producing complex metallic components with high precision, design freedom, and minimal material waste. Among the various categories of additive manufacturing processes, L-PBF stands out, paving the way for the execution of part designs with geometries previously considered unfeasible. Despite offering several advantages, parts with overhang features require the use of support structures to provide dimensional stability of the part. Support structures achieve this by resisting residual stresses generated during processing and assisting heat dissipation. Although the scientific community acknowledges the role of support structures in the success of L-PBF manufacturing, they have remained relatively underexplored in the literature. In this context, the present work investigated the impact of laser power and scanning speed on the dimensioning, integrity and tensile strength of single-walled block type support structures manufactured in AISI 316L stainless steel. The method proposed in this work is divided in two stages: processing parameter exploration, and mechanical characterization. The results indicated that support structures become more robust and resistant as laser power increases, and the opposite effect is observed with an increment in scanning speed. In addition, defects were detected at the interfaces between the bulk and support regions, which were crucial for the failure of the tensile test specimens. For a layer thickness corresponding to 0.060 mm, it was verified that the combination of laser power and scanning speed of 150 W and 500 mm/s resulted in the highest tensile resistance while respecting the dimensional deviation requirement. Full article

The experimental tests needed for the estimation of the fatigue limit generally require extensive time and many specimens. A valid but not standardized alternative is the thermographic analysis of the self-heating phenomenon. The present work is aimed at using Infrared thermography to determine the fatigue limit in two kinds of Ti-6Al-4V samples obtained by hot rolling: (1) with the standard dog-bone shape (unnotched specimen) and (2) with two opposed semicircular notches at the sides (notched specimen). Uniaxial tensile experiments are performed on unnotched samples, and the surface temperature variation during loading is monitored. The stress corresponding to the end of the thermoelastic stage gives a rough indication of the fatigue limit. Then, fatigue tests at different sinusoidal loads are performed, and the thermographic signal is monitored and processed. The results obtained using lock-in thermography in dissipative mode, e.g., analyzing the second harmonic, showed a sudden change in slope when the applied stress exceeded a certain limit. This slope change is related to the fatigue limit. In addition, the ratio between the fatigue limits obtained for notched and unnotched specimens, e.g., the fatigue strength reduction factor, is consistent with literature values based on the selected geometry. Full article

Prefabricated Ultra-High-Performance Concrete (UHPC) and cast-in-place Normal Concrete (NC) composite members are increasingly used in bridge engineering because they combine high performance with cost-effectiveness. The bond at the UHPC-NC interface is critical as it directly impacts the composite structure’s safety. This study employed 3D laser scanning acquired the UHPC substrate geometry, utilized fractal dimension analysis to quantify the interface roughness, and adopted the slant shear test to evaluate the effects of retarder application mass and hydration delay duration on roughness and bond strength. The research results indicate that the failure modes of UHPC-NC specimens can be categorized into interface shear failure and NC splitting tensile failure. With the extension of hydration delay duration, both the interface roughness and bond strength show a decreasing trend. The influence of retarder dosage on interface roughness and bond strength exhibits a threshold effect. This study also confirms the effectiveness of fractal dimension as a quantitative tool for characterizing the macroscopic roughness features of the bonding interface. The findings of this paper provide a solid theoretical basis and quantitative support for optimizing key process parameters such as retarder dosage and precisely controlling hydration delay duration, offering significant engineering guidance for enhancing the interface bonding performance of UHPC-NC composite structures. Full article

In the industrial practice of metal forming, the consistent and reasonable characterization of the material behavior under the coupling effect of strain, strain rate, and temperature on the material flow stress is very important for the design and optimization of process parameters. The purpose of this work was to establish an appropriate constitutive model to characterize the rheological behavior of a hot-formed steel plate (22MnB5 steel) produced through the TSCR (Thin Slab Casting and Rolling) process under practical deformation temperatures (150–250 °C) and strain rates (0.001–3000 s⁻¹). Subsequently, the material flow behavior was modeled and predicted using the Johnson–Cook flow stress constitutive model. In this study, uniaxial tensile tests were conducted on 22MnB5 steel at room temperature under varying strain rates, along with elevated-temperature tensile tests at different strain rates, to obtain the engineering stress–strain curves and analyze the mechanical properties under various conditions. The results show that during room-temperature tensile testing within the strain rate range of 10⁻³ to 300 s⁻¹, the 22MnB5 steel exhibited overall yield strength and tensile strength of approximately 1500 MPa, and uniform elongation and fracture elongation of about 7% and 12%, respectively. When the strain rate reached 1000–3000 s⁻¹, the yield strength and tensile strength were approximately 2000 MPa, while the uniform elongation and fracture elongation were about 6% and 10%, respectively. Based on the experimental results, a modified Johnson–Cook constitutive model was developed and calibrated. Compared with the original model, the modified Johnson–Cook model exhibited a higher coefficient of determination (R²), indicating improved fitting accuracy. In addition, to predict the material’s damage behavior, three distinct specimen geometries were designed for quasi-static strain rate uniaxial tensile testing at ambient temperature. The Johnson–Cook failure criterion was implemented, with its constitutive parameters calibrated through integrated finite element analysis to establish the damage model. The determined damage parameters from this investigation can be effectively implemented in metal forming simulations, providing valuable predictive capabilities regarding workpiece material performance. Full article

A novel approach to estimating the absorbed energy (toughness) in a uniaxial tensile test with only knowledge of the microstructure is presented. The flow behavior of each Dual-Phase (DP) steel grade is predicted using idealized Representative Volume Elements (RVEs) up to uniform elongation. To estimate the flow behavior beyond uniform elongation, the stress-modified fracture strain in a non-local damage model was implemented in Abaqus. Damage parameters were calibrated using Finite Element (FE) simulations of purely ferritic tensile specimens. The damage parameters remained unchanged, except for the coefficient of triaxiality. This coefficient was adjusted based on the average triaxiality of ferrite elements at the instability point of the uniaxially loaded RVEs for each DP steel grade. The proposed approach comprises two steps: micron-sized RVEs to predict the flow behavior up to the point of uniform elongation and the average triaxiality and full-scale tensile-test simulations to predict the rest of the curves. The results show that the damage parameters calibrated for high-strain ferrite effectively estimate the absorbed energy during failure in tension tests. This approach is also geometry-independent; varying the geometry of the tensile specimen, including miniature or notched specimens, still yields predicted absorbed energies that are in good agreement with the experimental results. Full article

The initiation of ductile fractures in medium-strength AW5754 and high-strength AW6082 aluminum alloys at different quasi-static strain rates and under multiaxial stress states was investigated through a series of tensile tests using various specimen geometries. The sensitivity of the stress triaxiality locus to variations in the loading rate was examined for these two aluminum alloy families. Fractographic and elemental analyses were also conducted via SEM and EDS. Numerical simulations based on the finite element method (FEM) were performed using ABAQUS/Standard to determine the actual stress triaxialities and the equivalent plastic strains at fracture. The numerical approach was validated by comparing the simulation results with the experimental findings. These simulations facilitated the generation of a stress triaxiality locus through a curve-fitting process. Among the considered fitting functions, an exponential function was selected as it provided the most accurate relation between the equivalent plastic strain at fracture and the corresponding stress state across different strain rates. The results reveal different strain rate dependencies for the two alloys within a very low strain rate range. The resulting stress triaxiality loci provide a valuable tool for predicting fracture strains and for more accurately evaluating stress states. Overall, the findings of this study significantly advance the understanding of the fracture initiation behavior of aluminum alloys under multiaxial loading conditions and their sensitivity to various quasi-static loading rates. Full article

Magnesium (Mg) alloys are gaining widespread use in the automotive and construction industries for their potential to enhance performance and lower manufacturing costs, making them ideal for lightweight structural applications. However, despite these advantages, extruding Mg alloys remains technically challenging due to their inherently limited formability and the strong crystallographic textures that form during deformation. This study aimed to comprehensively characterize the ductile fracture behavior of ZM51M Mg alloy round bars under various stress states and to improve the reliability of ductile failure predictions through the application and calibration of multiple uncoupled damage criteria. Tensile and compressive tests were conducted on specimens of varying geometries (dogbone, notched R5, shear, uniaxial compression, and plane strain compression specimens) and dimensions, meticulously cut along the extrusion direction of the round bar. These tests encompassed a wide spectrum of stress–strain responses and fracture characteristics, including uniaxial tension, uniaxial compression, and shear-dominated states. An inverse analysis approach, involving iterative numerical simulation coupled with experimental data, was employed to precisely determine fracture strains from the test results. The plastic deformation behavior was accurately modeled using the combined Swift–Voce hardening law. Subsequently, three prominent uncoupled ductile fracture criteria—Rice–Tracey, DF2014, and DF2016—were calibrated against the experimental data. The DF2016 criterion demonstrated superior predictive accuracy, consistently yielding the most accurate fracture strain predictions and significantly outperforming the Rice–Tracey and DF2014 criteria across the tested stress states. The findings of this work provide significant insights for improving the assessment of formability and fracture prediction in Mg alloys. This research directly contributes to overcoming the challenges associated with their inherent formability limitations and complex deformation textures, thereby facilitating more reliable design and broader adoption of Mg alloys in advanced lightweight structural solutions. Full article

Variations in the warm formability of AA7075 sheets are primarily attributed to differences in precipitate morphology resulting from distinct thermal histories. To better understand this relationship, this study systematically investigates the influence of precipitate characteristics—quantified by the product of precipitate volume fraction and average radius—on forming limits across various thermal routes in warm forming processes. A modified Cockcroft–Latham ductile fracture model incorporating this microstructural parameter was developed, calibrated against experimental data from warm isothermal Nakajima tests, and implemented within a finite element framework. The proposed model enables the accurate prediction of forming limit curves with minimal experimental effort, thereby significantly reducing the reliance on extensive mechanical testing. Building upon the validated FE model, a practical methodology for rapid R-value estimation under warm forming conditions was established, involving the design of specimen geometries optimised for isothermal Nakajima testing. This approach achieved R-value predictions within 5% deviation from conventional uniaxial tensile test results. Furthermore, experimental results indicated that AA7075 sheets exhibited nearly isotropic deformation behaviour under retrogression warm forming conditions. Overall, the methodology proposed in this study bridges the gap between formability prediction and process simulation, offering a robust and scalable framework for the industrial optimisation of warm forming processes for high-strength aluminium alloys. Full article

Complete dentures are exposed to complex masticatory forces that may lead to material fatigue and eventual structural failure. Occlusal relationships, such as eugnathic and progenic, influence the distribution of these forces significantly. Understanding their biomechanical impact is essential for improving denture design and longevity. The aim of this study was to evaluate the mechanical behaviour of complete dentures under bite loads in eugnathic and progenic occlusal relationships, using both experimental testing and numerical simulations. The focus was placed on identifying the conditions that lead to initial damage and the patterns of stress distribution. The material properties of the denture base and artificial teeth were determined through experimental tensile and compressive testing on cylindrical PMMA specimens. The denture geometry was acquired via 3D tomography based on impressions of an edentulous patient. Experimental testing of the denture bite was conducted to determine the force thresholds at which the initial cracks occur. Numerical simulations were carried out using finite element analysis at bite loads of 100 N and 200 N in both occlusal types, incorporating the obtained material parameters. The experimental results showed that the first signs of denture damage occurred at 6400 N in eugnathic occlusion and 7010 N in progenic occlusion. The numerical simulations confirmed that, during occlusion, the pressure is redistributed across multiple contact points, with a broader distribution reducing the localised stress. This redistribution was more efficient in eugnathic occlusion, which reduced the risk of longitudinal cracking in acrylic teeth. In contrast, progenic occlusion showed higher susceptibility to fractures within the acrylic denture base, particularly between adjacent teeth. Both the experimental and numerical approaches demonstrated that occlusal relationships affect the mechanical resilience of complete dentures directly. The findings highlight that eugnathic occlusion offers biomechanical advantages in stress distribution, potentially reducing the risk of fracture. Incorporating occlusal analysis into denture design protocols can enhance clinical outcomes and improve prosthetic longevity. Full article