Experimental Tensile Tests Research Articles

Surrogate metamodels from digital image correlation for testing high-performance composite vessels

In this work, a workflow has been developed for the generation of surrogate metamodels to predict and evaluate failure with a confidence above 95 % in initial service conditions of high-performance cylindrical vessels manufactured in composites by Roll Wrapping technology. Currently, there is no specific testing standardization for this type of vessel and to fill this gap probabilistic numerical models were developed, performed by the Finite Element Method, fed with the material characteristics obtained experimentally by 2D digital image correlation from flat specimens. From the initial numerical model, a surrogate metamodel was generated by stochastic approximations. Once the metamodels were obtained by robust engineering, an experimental ring-ring tensile test was developed under service conditions and deformations were measured by high-precision 3D digital image correlation. Parametric and robust tests showed that the results of the metamodel did not show statistically significant differences, with errors in the rupture part of less than 2 % with respect to the results obtained in the test, being proposed as a basis for new test procedures.

Mechanical Properties of Virgin and Recycled Polymer for Construction Pile Application

Annual polymer waste generated in Malaysia has increased significantly to more than 1 million tonnes. The prolonged degradation periods required by diverse industrial polymer waste streams are a matter of significant concern, with some taking up to 1000 years to fully degrade. Pursuing a similar environmental concern, the use of bakau piles as supports for lightweight structures in Sarawak, including drainage systems, roads, sewerage, and other water-related structures, has become a matter of concern due to the deforestation of mangrove forests. Both bakau deforestation and polymer waste issues are significant environmental and global concerns. The idea of mitigating mangrove degradation and the non-biodegradable nature of polymer waste has led to the conceptualization of an alternative solution whereby recyclable thermoplastic polymer piles are utilized to supplant bakau piles in providing support for lightweight structures during civil engineering construction projects. Therefore, the study of polymer piles is conducted to examine their mechanical properties in the form of virgin (V) and recycled (R) thermoplastic polymers. In this study, high-density polyethylene (HDPE), polypropylene (PP), and polyvinyl chloride (PVC) are considered, and the possibility of being utilized in pile application has been discussed. Based on the results, all virgin types of thermoplastic polymers (HDPE, PP, and PVC), 50%V:50%R for PP, PP(R), and PVC(R), respectively, exceed the bakau ultimate tensile strength. Thermoplastic polymer piles showed great potential to be the substitution for bakau piles to serve in the construction industry, with the recorded experimental tensile and compressive strength tests.

Flow curve approximation of high-strength aluminium alloys in heat-assisted forming processes

Predicting the flow behaviour at high strain values beyond uniform elongation is a critical factor in sheet metal forming, especially in the context of heat-assisted forming processes of lightweight materials. Based on uniaxial tensile tests conducted at the temperature profiles of the Hotforming, W-Temper, and Warmforming process routes this study presents the determination of the flow curve for EN AW-7021 sheet material using five commonly used empirical approximation models. A support point obtained from layer compression tests was introduced to analyse the accuracy of the extrapolation models at higher strain values. All models considered were found to be in good agreement with the experimental tensile test data in the area of uniform elongation. However, the empirical approximation models show significant differences in strain hardening behaviour when higher strain values and varying temperature profiles are considered. For the Hotforming and W-Temper process routes, the Hockett-Sherby model estimates the flow behaviour with the highest accuracy. When using the Warmforming process, all approximation models considered seem to estimate the flow behaviour with reasonable accuracy, however the Ludwik-Hollomon modified equation shows the best correlation with the experimental data.

Hydrogen Embrittlement Characterization of 1.4614 and 1.4543 Martensitic Precipitation Hardened Stainless Steels

Hydrogen embrittlement (HE) of 1.4614 and 1.4543 maraging stainless steels is characterized with fine structural TEM-ASTAR, hydrogen electrochemical permeation, thermodesorption and tensile testing (with slow strain rate during H cathodic charging) experiments. Both solutions annealed and 550 °C aged states are studied. When aged, 1.4614 grade contains nanometric hexagonal Ni3Ti precipitates whereas 1.4543 grade contains three families of nanometric precipitates, namely, hexagonal Ni3Ti, non fcc-rich Cu and G-phase rich in Si, Ti and Ni with cube-cube relations with martensite. From the permeation and thermodesorption results, it appears that austenite and nanometric precipitates seem to constitute deep traps for hydrogen in both grades. From tensile tests with in situ H charging, 1.4614 and 1.4543 maraging grades show a high susceptibility to HE with relative reduction of area (RRA) strictly superior to 80% for both metallurgical states. The presence of retained austenite does not seem to bring any HE resistance because of its transformation into martensite during deformation.

Design of a multi-modal sensor for the in-process measurement of material properties based on inductive spectroscopy

Ferromagnetic steel magnetic properties undergo isotropic and anisotropic changes during cold forming processes. Although their measurement provides an important basis for material property-controlled process control, it remains particularly challenging, as workpieces are subjected to several influencing effects, such as tilting and distance to the target. In this paper, we propose a robust contactless multi-modal sensor for the in-process measurement of material magnetic properties composed of a central excitation coil surrounded by eight receiving coils. The material magnetic permeability is measured based on a model-based evaluation of the central coil inductance spectrum compensating for the influence of the distance to the target. The sensor realizes a measurement of the magnetic anisotropy independently of the tilting effects based on an FFT-based analysis of the induced voltage in the peripheral coils. The sensor has been validated in a tensile test experiment on standard specimens. The measurement data of the tensile test reveal a systematic relation of permeability and magnetic anisotropy to the mechanical influences of stress and deformation. The measurements remained stable despite strong movements between the sensor and the target. A working distance increase of 80% resulted in variations of the magnetic permeability of only 3%. The observed changes in magnetic anisotropy are uncorrelated to tilting effects. Based on the investigation results a proposal for the design of an in-process measurement system is provided.

Bottom-to-top modeling of epoxy resins: From atomic models to mesoscale fracture mechanisms.

We outline a coarse-grained model of epoxy resins (bisphenol-F-diglycidyl-ether/3,5-diethyltoluene-2,4-diamine) to describe elastic and plastic deformation, cavitation, and fracture at the μm scale. For this, molecular scale simulation data collected from quantum and molecular mechanics studies are coarsened into an effective interaction potential featuring a single type of beads that mimic 100nm scale building blocks of the material. Our model allows bridging the time-length scale problem toward experimental tensile testing, thus effectively reproducing the deformation and fracture characteristics observed for strain rates of 10-1 to 10-5s-1. This paves the way to analyzing viscoelastic deformation, plastic behavior, and yielding characteristics by means of "post-atomistic" simulation models that retain the molecular mechanics of the underlying epoxy resin at length scales of 0.1-10 µm.

Model for Wastage Allowance and Strength Properties of Pipe Piles Exposed to Marine Corrosion

The study’s objective is to analyze the mechanical properties of steel pipe piles as a part of a trestle bridge subjected to five years of natural marine corrosion degradation. Sixteen tensile specimens are extracted from the steel pipe piles in the splash, tidal, and immersion zones. The experimental tensile test results are used to establish regression equations defining the elastic modulus, yield strength, strain hardening index, and strength coefficient for the true stress–strain curves of the three regions. A non-linear time-dependent mathematical model is exploited to identify the corrosion degradation, using the data from one single corrosion degradation measurement campaign. The analysis indicates that the splash zone is experiencing the most severe corrosion degradation, and there are progressive losses in the mechanical properties of each zone as the corrosion degradation progresses. The established relationships of the mechanical properties, as a function of the ratio of corroded plate thickness to the as-built one, can be used as a fast-engineering approach to identify the mechanical properties of severely corroded piles. The corrosion degradation allowance is also defined using the first-order reliability method, accounting for existing uncertainties covered by the partial safety factors. By examining the impact of marine corrosion on the mechanical properties of marine structures and developing predictive models to assess the corrosion’s effect on material strength and corrosion allowance, the study aims to improve offshore structures’ safety, design, and maintenance.

3D-printing technology for integrating the rehabilitation and monitoring of civil structures with fiber optic

In recent years, 3D printing technologies have become increasingly widespread in the field of architectural restoration of historical buildings and monuments. This is due to 3D printing’s capability to accurately reproduce complex shapes with simplicity. Currently, within this field, 3D printing technology is generally employed for the physical reproduction of decorative/architectural components, while the reproduction of structural elements is still in its early stages. In this context, the paper presents an experimental study on 3D-printed samples made of PLA (Polylactic Acid Material), equipped with fiber optic sensors introduced inside the samples during the printing process. This innovative approach facilitates reintegration interventions while enabling real-time monitoring of structures, marking a significant advancement in the field. However, since the fiber optic is incorporated within the element during the printing process, it is crucial to assess its potential impact on the mechanical properties of the samples and reliability of measurement system itself. Experimental tensile tests are then performed on samples carried out by considering both different printing paths and, moreover, different arrangements of the fiber optic inside the samples. Lastly, the study also examines the impact of artificially induced aging effects to assess their influence on both the mechanical properties of the samples and the reliability of measurements obtained from the fiber optic sensors.

Development of Interactive Virtual Reality Application for Simulating Experimental Tensile Test

Information technology has significantly transformed traditional educational systems into adaptable forms of learning. Experimental tension test is a practical study included in the mechanical engineering curriculum, specifically as a part of Material and Metallurgy. The fundamental issue arises from the deficiency in comprehending the understanding of mechanical properties, which is a result of traditional educational methods. Virtual reality (VR) technology enhances the comprehension of the study of material properties for students studying mechanical engineering. This study presents a virtual reality tool, called VR experimental tensile test. It is intended to be utilized in flexible learning. Students as a user can investigate and examine the utilization of the program for learning and conducting safety lab orientation. The application evaluation was conducted using the User Experience Questionnaire (UEQ). This study suggests that using 3D model visualization in the virtual reality application enhances user experiences in learning tensile test and follow its lab orientation.

Tailoring microstructures and properties in Co-free FeNiCrCuAl high entropy alloys by Al addition

In this study, a series of Co-free FeNiCrCuAlx (x = 0.1, 0.3, 0.5, 0.8 and 1.0) high entropy alloys (HEAs) were developed by vacuum arc melting and casting method in high-purity argon atmosphere. The effects of Al addition on the microstructure and properties were investigated using X-ray diffraction, scanning electron microscopy, Vickers hardness tester, tensile test, wear test and electrochemical experiment. It was found that with the increase in the large atomic-sized Al content, the closely-packed FCC structure was destabilized for a transition to the loosely-packed BCC structure at x = 0.3. As x increased up to 1.0, the structure was mainly composed of BCC phase. The hardness of HEAs was enhanced by the influence of the contiguous atomic planes in BCC structures due to the relatively lower inter-planar spacing and higher lattice friction for dislocation motion, with the potential to increase the yield strength of the HEAs by 93.5 %. The friction coefficient decreased with increasing Al content, as indicated by stable profiles of Al0.8 and Al1.0 under progressive wear in comparison to those of Al0.1, Al0.3 and Al0.5 while the associated minimal wear depth and lower capacity for debris accumulation of the higher Al content HEAs confirmed their superior wear resistance. As FeNiCrCuAl0.5 presented the most superior corrosion resistance due to high resistance to ionic transport via the steady oxide film and the indication of a comparatively wider capacitive semicircle, undue Al additions would not be beneficial to improving plasticity or enhance corrosion resistance. Thus, FeNiCrCuAlx HEAs with Al contents in the range of 0.5–1.0 were found to possess optimized comprehensive properties, and can be suitably recommended as nuclear structural materials. This study will shed light on advancing the development of cutting-edge HEAs.

The Influence of Tool Rotational Speed on Mechanical Properties of Friction Stir Welded Dissimilar AA5083-H112/AA6061-T6 Joints

The relatively new and innovative welding technique known as friction stir welding (FSW) has found widespread application in the automotive, railway, and aircraft industries. Due to engineering and financial considerations, welding of dissimilar metals is frequently carried out in these industries. During the friction stir welding process, three tool rotational speeds—910, 1500, and 2280 rpm—were utilized, while the welding speed remained constant at 30 mm/min. Several experimental works, including fractography, tensile tests, and observations of the microstructure, were carried out following welding. Results showed that ultimate tensile strength (UTS) and yield strength (YS) expanded as the tool rotational speed was expanded and the best UTS and YS, typically 228 MPa and 156 MPa at the speed of 2280 rpm. The precipitation of AA6061-T6 in the stir zone (SZ) and the increased degree of mixing were linked to the improved weld strengths.

Effect of Fiber Sizing Levels on the Mechanical Properties of Carbon Fiber-Reinforced Thermoset Composites.

Fiber sizing is one of the most important components in manufacturing composites by affecting mechanical properties, including strength and stiffness. The sizing of manmade fibers offers many advantages, such as improving fiber/matrix adhesion and bonding properties, protecting fiber surfaces from damage during the processing and weaving stages, and enhancing the surface wettability of polymer matrices. In this work, the influence of fiber sizing levels on carbon fibers' (CFs) mechanical properties is reported at room temperature using single fiber tensile testing (Favimat+), single fiber pullout testing (SFPO), and interfacial elemental analysis by X-ray photoelectron spectroscopy (XPS). Standard modulus CFs (7 ± 0.2 μm in diameter) were sized using two commercially available Michelman sizing formulations. The average solid content for each sizing formulation was 26.3 ± 0.2% and 34.1 ± 0.2%, respectively. HEXION RIMR 135 with curing agent RIMH 137 was used as a model thermoset epoxy matrix during SFPO measurements. A predictive engineering fiber sizing methodology was also developed. Sizing amounts of 0.5, 1, and 2 wt.% on the fiber surface were achieved for both sizing formulations. For each fiber size level, 50 single-fiber tensile testing experiments and 20 single-fiber pull-out tests were conducted. The ultimate tensile strength (σult) of the carbon fibers and the interfacial shear strength (τapp) of the single fiber composite were analyzed. The sizing levels' effect on interfacial shear stress and the O/C (Oxygen/Carbon) surface composition ratio was investigated. Based on our experimental findings, an increase of 6% in fiber performance was recorded for ultimate tensile and interfacial shear strengths. As a result, generalized fiber sizing and characterization methods were established. These developed methods can be used to characterize the strength and interfacial shear strength of manmade fibers with different sizing formulations and solid contents irrespective of the matrix, i.e., thermoset or thermoplastic.

In situ mechanical testing of hard yet tough high entropy nitride coatings deposited on compliant steel substrates

High entropy nitrides are an interesting material class for wear resistant coatings. Their fracture properties and toughness are of particular interest for future application in tool coatings. Therefore, in situ tensile testing and micro-cantilever experiments were performed on (AlCrTaTiZr)N, (AlCrNbSiTiV)N, (HfNbTaTiVZr)N and (AlTi)N coatings inside a scanning electron microscope. Parallel cracks form during tensile testing from which the fracture toughness was determined via a modified Hsueh and Yanaka model. For this the misfit strain between coating and substrate was treated as an unknown parameter and was fitted to the beginning part of the underlying crack density – applied strain curves. The validity of the model was evaluated by comparing the results with fracture toughness values derived via micro-cantilever bending experiments. A good fit between the data could be observed for three out of four tested coatings. The limitations of the underlying analytical model are presented and discussed. The tested high entropy nitride coatings displayed a promising combination of high hardness and fracture toughness.

The elasto-plastic numerical study of crack initiation in notched PMMA specimens under uniaxial loading conditions – Tension and torsion

This paper presents the results of FEM numerical calculations aimed at describing the plastic strain and stress fields under critical loading conditions: tensile force or torsional moment. The calculations were carried out with reference to the results of experimental tensile and torsional tests of flat PMMA specimens weakened with V-notches of different root radii: 0.5, 2 and 10 mm. The procedure for conducting nonlinear numerical analyses is described, including the determination of the actual hardening curve by the hybrid method. A high level of consistency between the results of the experimental and numerical calculations was obtained through description of PMMA with the elastic–plastic material model. The points of occurrence of stress maxima and plastic strain were indicated, which were taken as potential crack initiation sites. On the basis of the stress and plastic strain values measured at the critical points, a stress–strain fracture criterion was formulated, which was then positively verified.

How epoxy cure profiles (may) impact performance of non-crimp fabric composites

Glass fibre reinforced polymers made from quasi uni-directional non-crimp fabrics have recently been shown to suffer from a specific damage mechanism. This damage mechanism is dominated by off-axis cracks in the off-axis backing bundles of the fabrics. In addition, research results have indicated that the onset and propagation of such off-axis cracks may be influenced by the residual stresses that arising from the manufacturing process used to produce the Glass fibre reinforced composites. The current article investigates the potential effect of residual stresses on the fatigue life through an experimental set-up that involves tailored cure profiles and image based evaluation of tensile test experiments.

Structural Mechanics Analysis of Woven Web Reinforced Membranes in Proton Exchange Membrane Water Electrolysis

Abstract Membranes are a key component of proton exchange membrane water electrolysis (PEMWE) cells and are exposed to various stressors during operation, which can significantly reduce cell lifetime. PEMWE membranes incorporating woven web layers within the membrane structure for mechanical reinforcement are a promising, commonly-used industrial strategy to mitigate the formation of membrane defects. Here, the structural mechanics of a PEMWE cell were investigated, specifically the woven web reinforced membrane. Experimental tensile tests were conducted on the membrane to obtain stress-strain data. These measurements were utilized to parameterize a geometrically simplified model of the woven web reinforced membrane through a tensile test simulation. The validated model was applied in a 2D-cell simulation to identify resulting stresses and strains in the membrane during various electrolysis operation modes. The results herein allow the used PEMWE cell geometry to be systematically evaluated and optimized with respect to mechanical membrane stability. For the applied PEMWE cell setup, no failure is expected during normal operation, including varied temperatures and differential pressure. Increasing the gap size at the edge of the electrochemically active cell area, however, leads to large deformations when the gap becomes larger than 0.2 mm.

Comparative Studies on Mechanical Properties and Corrosion Rate of Nickel Chromium Carbide (Cr3C2-NiCr) Coated on Inconel 600, 625, 718 Specimen

In this present work, Nickel Chromium Carbide (Cr3C2-NiCr) coated on three different Inconel 600, 625, 718 Specimen are used and the mechanical properties, corrosion resistance and morphological properties of the specimen were investigated by conducting Brinell hardness test, Vickers Hardness Test, Tensile test and electrochemical test experiments respectively and found that Inconel 625 has maximum hardness, maximum tensile strength and less corrosion resistance as compared to the remaining two coated Inconel specimen 600 & 718. And then coated surfaces of Inconel 600, 625 and 718 specimens were analyzed by using Scanning Electron Microscope (SEM), XRD, EDAX and optical microstructure techniques.

Experimental and Numerical Investigation into the Mechanical Behavior of Composite Solid Propellants Subject to Uniaxial Tension.

To further explore the quasi-static mechanical characteristics of composite solid propellants at low strain rates, an investigation was conducted on the mechanical behavior and damage mechanisms of a four-component hydroxy-terminated polybutadiene (HTPB) propellant by means of experiments and numerical simulation. A uniaxial tensile test and scanning electron microscope (SEM) characterization experiment were carried out. A microstructural model, which accurately represents the mesoscopic structure, was developed via the integration of micro-CT scanning and image-processing techniques. The constructed microstructural model was utilized to conduct a numerical simulation of the mechanical behavior. The experimental results demonstrated that the maximum tensile strength increases with increasing strain rate, and the primary cause of propellant failure at low strain rates is the dewetting phenomenon occurring at the interface between the larger particles and the matrix. The maximum tensile strength is 0.48 MPa when the strain rate is 0.00119 s-1, and the maximum tensile strength is 0.37 MPa when the strain rate is 0.000119 s-1. The simulation results indicated a consistent trend in variation when comparing the simulation and experimental curves. This suggested that the established model exhibits a high level of reliability, and provides a promising approach for carrying out microstructural simulations of heterogeneous propellants in future. The mechanical behavior of the propellant can be effectively described by utilizing a mesoscopic finite element model that incorporates the superelastic constitutive model of the matrix and the bilinear cohesive model. This framework facilitates the representation of mesoscopic damage evolution, which consequently provides insights into the damage mechanism. Additionally, the utilization of such models assists in compensating for the limitations of damage evolution characterization experiments.

Injury risk functions for the four primary knee ligaments.

The purpose of this study was to develop injury risk functions (IRFs) for the anterior and posterior cruciate ligaments (ACL and PCL, respectively) and the medial and lateral collateral ligaments (MCL and LCL, respectively) in the knee joint. The IRFs were based on post-mortem human subjects (PMHSs). Available specimen-specific failure strains were supplemented with statistically generated failure strains (virtual values) to accommodate for unprovided detailed experimental data in the literature. The virtual values were derived from the reported mean and standard deviation in the experimental studies. All virtual and specimen-specific values were thereafter categorized into groups of static and dynamic rates, respectively, and tested for the best fitting theoretical distribution to derive a ligament-specific IRF. A total of 10 IRFs were derived (three for ACL, two for PCL, two for MCL, and three for LCL). ACL, MCL, and LCL received IRFs in both dynamic and static tensile rates, while a sufficient dataset was achieved only for dynamic rates of the PCL. The log-logistic and Weibull distributions had the best fit (p-values: >0.9, RMSE: 2.3%-4.7%) to the empirical datasets for all the ligaments. These IRFs are, to the best of the authors' knowledge, the first attempt to generate injury prediction tools based on PMHS data for the four knee ligaments. The study has summarized all the relevant literature on PHMS experimental tensile tests on the knee ligaments and utilized the available empirical data to create the IRFs. Future improvements require upcoming experiments to provide comparable testing and strain measurements. Furthermore, emphasis on a clear definition of failure and transparent reporting of each specimen-specific result is necessary.

Effect of raster and layer characteristics on tensile behavior and failure of FFF printed PLA samples by representative volume element model

In the fused filament fabrication (FFF) based additive manufacturing process, finding optimum printing parameters for achieving the required mechanical properties of the FFF-built part is challenging. In this study, a representative volume element (RVE) based mesoscale approach was developed to describe the influences of printing parameters on the mechanical behaviors of the 3D printed parts. It was shown that the stress-strain curves up to failure obtained from RVE simulations were well verified by experimental tensile test data of printed PLA samples. Then, effective tensile properties of samples manufactured using different raster angles (0°, 45°/−45°, and 90°) and a wide range of layer heights and widths were predicted and correlated with their respective local damage occurrences. The raster angle strongly affected the elastic modulus and tensile strength. The orientation between interlayer voids and loading direction governed local stress distribution, interface failure, and total deformation of FFF samples. An increased layer height and decreased layer width resulted in a more significant fraction of voids between layers and thus lowered stiffness and tensile strength. The introduced RVE model can serve as a simple tool for determining homogenized responses and studying local stress-strain developments and failure of complex printed parts according to the used printing parameters.