Quasi-static Tensile Experiments Research Articles

Thermomechanical characterisation and plane stress linear viscoelastic modelling of ethylene-tetra-fluoroethylene foils

AbstractEthylene-tetra-fluoroethylene (ETFE) is a polymer employed in tension membrane structures with mechanical properties that strongly depend on time and temperature effects. A comprehensive understanding of the mutual influence of these variables and a unified viscoelastic constitutive model design can enable wider exploitation of ETFE in sustainable lightweight construction. This study presents a thermomechanical characterisation of ETFE foils through quasi-static tensile experiments spanning two orders of magnitude of strain rates, creep, relaxation, shear and dynamic cyclic tests in a wide range of temperatures suitable for building applications, from $-20^{\circ }\text{ C}$ − 20 ∘ C to $60^{\circ }\text{ C}$ 60 ∘ C . The experimental results in different material orientations are used to identify the limits of the linear viscoelastic domain, define the direction-dependent creep compliance master curves and calibrate the parameters of a plane stress orthotropic linear viscoelastic model, employing the Boltzmann superposition and the time-temperature superposition principles. The model has been numerically implemented using a recursive integration algorithm and its code is provided open source. A validation on independently acquired data shows the accuracy of the constitutive model in predicting ETFE behaviour within the linear viscoelastic regime usually adopted during structural design, with excellent extrapolation capabilities outside the range of the calibration data.

The modified Swift constitutive model of 304L stainless steel at the cryogenic temperature based on the Olson–Cohen model

The nonlinear behavior of austenitic stainless steel (ASS) is significantly affected by the temperature and strain during plastic deformation. However, the conventional constitutive model is often inadequate to accurately describe its mechanical properties, particularly at cryogenic temperatures. Therefore, the development of a constitutive model for ASS at cryogenic temperatures is of paramount importance in order to fully understanding the performance of liquefied natural gas (LNG) membrane tank structures under such conditions. In this study, we have derived a modified constitutive model using 304L stainless steel that incorporates a phase transition model through theoretical derivations. First, the stress and strain data for 304L stainless steel within the range of 108–293 K have obtained from quasi-static tensile experiments. Subsequently, the XRD test results are utilized to calculate the volume fraction of martensite across various temperatures and strains. Next, a modified constitutive model is proposed by combining the Olson–Cohen phase transition model and the Swift constitutive model. Finally, the accuracy of the modified Swift constitutive model is verified through experimental data. The results demonstrate that the modified Swift constitutive model is precise for characterizing the properties of 304L stainless steel across a wide range of temperatures. Furthermore, multiple case studies have proven the feasibility of using the modified Swift constitutive model to predict the properties of various austenitic materials. By incorporating the Olson-Cohen phase transition model, the modified Swift constitutive model showcases its wide applicability and potential in designing and assessing the safety of ASS structures.

Dynamic strengthening of UHMWPE yarns by incorporating ZrO2/PU coatings

Wrapping is an effective technique for reducing defects in fabric weaving and promoting even wetting in composite manufacturing, which is potential to enhance the impact resistance of armor materials. In this study, we impregnated UHMWPE yarns with a polyurethane (PU) compound and cured them to create composite yarns, and ZrO2 was introduced to improve the toughness. The microstructures were analyzed using three-dimensional X-ray computed tomography, optical microscopy, and scanning electron microscopy (SEM). Quasi-static and dynamic tensile experiments were conducted using a universal testing machine and Kolsky tension bar, respectively. High-speed imaging was used to capture the real-time failure process, and post-fracture analysis was performed to examine the fracture morphology. The effects of strain rate, gauge length, and the presence of PU and ZrO2 on the mechanical behavior of the yarns were investigated. The results showed that the peak force of the composite yarns with PU coatings exhibited strain-rate dependency at low strain rates (below 4.4 × 10−2 s−1) but became insensitive to strain rate in the higher range of 4.4 × 10−2 s−1 to 1500 s−1. Furthermore, the introduction of ZrO2 effectively increased the peak force, potentially by strengthening the bonding between individual fibers within the yarn.

Investigation on dynamic deformation behavior of 7A75 aluminum alloy over wide strain rates and constitutive model establishment

The aluminum alloy components on automobile often experience high strain rate deformation during accidents. The dynamic deformation behavior and constitutive model are crucial for analysis of vehicle body collisions and failures. In this work, the 7A75 aluminum alloy plate was heat treated according to standard body manufacturing procedures. Quasi-static and dynamic tensile experiments were conducted on the aged 7A75 alloy in a wide strain rate range from 0.001 s−1 to 500 s−1. The dynamic deformation behavior of the alloy was revealed, and the constitutive models were established. It was found that the 7A75 alloy has strong strain rate sensitivity, and its mechanical properties can be significantly improved with the increase of strain rate. As the strain rate increases, the necking instability strain shifts towards higher values, which leads to a larger uniform deformation ability and fracture elongation. This behavior results in a better energy absorption capacity at high strain rates, thus providing a good collision protection property. The constitutive models, including Johnson-Cook (J-C) and Zerilli-Armstrong (Z-A) types, were established and compared. Note that the conventional J-C and Z-A models exhibit severe prediction distortion. Therefore, a modified J-C model incorporating strain rate compensation was introduced, which decrease the errors by 149% and achieves accurate predictions of both dynamic and static deformation behaviors over a wide range of strain rates.

Thermomechanical characterisation of a thermoplastic polymer and its short glass fibre reinforced composite: Influence of fibre, fibre orientation, strain rates and temperatures

Polycarbonate composites are widely used in products exposed to high strain rate deformation. This paper investigates the thermomechanical properties of polycarbonate and 20 wt% glass fibre reinforced polycarbonate to provide characterisation data and improved mechanistic understanding of the response to load, supported by Dynamic Mechanical Analysis and time–temperature superposition. Compressive behaviour is characterised from 0.001 to 5000 s−1 at room temperature and from −60 to 120 °C at 0.01 s−1; and a thermal imaging camera used to obtain temperature rise data. Quasi-static tensile experiments were also performed in different orientations relative to the injection flow direction. High-rate compression experiments are performed with X-ray imaging. As well as information about rate dependence of yield stresses and softening in the two materials, these data show how adiabatic shear band formation can cause significant softening in the composite. These data will enhance application of these polymers and facilitate development of advanced thermo-mechanical models.

Dynamic Tensile Behavior of Laser-Directed Energy Deposition and Additive Friction Stir-Deposited AerMet 100

Quasi-static and high-rate tensile experiments were used to examine the strain rate sensitivity of laser-directed energy deposition (L-DED)- and additive friction stir deposition (AFSD)-formed AerMet 100 ultrahigh-strength steel-additive manufactured builds. Electron backscattered diffraction (EBSD) revealed similar as-deposited grain sizes between the two AM processes at approximately 24 μm and 17 μm for the L-DED and AFSD samples, respectively. The strain hardening rate, θ, revealed little change in the overall hardening observed in the L-DED and AFSD materials, with a consistent hardening in the quasi-static samples and three identifiable regions in that of the high-rate tested materials. The L-DED deposited materials displayed average ultimate tensile strength values of 1835 and 2902 MPa for the 0.001 s−1 and 2500 s−1 strain rates, respectively and the AFSD deposited materials displayed ultimate tensile strength values of 1928 and 3080 MPa for the 0.001 s−1 and 2500 s−1 strain rates, respectively. Overall, the strength for both processes displayed a positive strain rate sensitivity, with increases in strength of ~1000 MPa for both processes. Fractography revealed significant solidification voids in the laser DED material and poor layer adhesion in the AFSD material.

Effect of Preload on Tensile Fracture of Variable Cross-Section Bolts: Experiment and Simulation

High-strength bolts are widely used in structural connections, and the preload affects the failure behavior of bolts. In this paper, a variable cross-section bolt (VCSB) with weakened strength to induce fracture is designed. Quasi-static tensile experiments with different preload torque values were performed on the VCSB. The preload torques of 0, 430, 610, and 820 N·m were applied to the VCSB connection structures before the test. The load–displacement curves obtained by the test could be divided into three stages: the initial elastic phase, the yield phase, and the rapidly necking phase. As the preload increased, the stiffness of the initial elastic phase increased from 101.21 kN/mm to 270.64 kN/mm and the fracture displacement DC decreased from 10.54 mm to 8.42 mm. Finite element models were developed to simulate the failure process of VCSB under tensile loads. The difference between the FB and DC values in the simulation results and the test is within 2%. The simulations were carried out by adjusting the prestress from 0 to 650 MPa. The results show that the value of preload force has no effect on the FB of VCSB, but greatly influences the DC and FC of the connection.

Mechanical properties of steel wires of 1670 MPa, 1770 MPa, and 1860 MPa grades under high strain rates and temperatures

In this study, the mechanical behavior under high strain rates and high temperatures of 1670 MPa, 1770 MPa, and 1860 MPa grades steel wires were investigated. Quasi-static tensile experiments (10−4 s−1), split Hopkinson compression bar experiments (102–103 s−1) and high-temperature tensile experiments were conducted (20–900 °C). A total of 89 samples were tested for the study. Stress-strain curves were obtained for different strain rates and different temperatures. The experiments indicated that the strain rate had an obvious influence on the behavior of high-strength steel wires, both the yield and ultimate strength increased with increasing strain rate. The strength ratio and strain rate sensitivity coefficients of high-strength steel wires were investigated for high strain rates. The mechanical properties of the steel wire are significantly reduced under high temperatures. The Cowper-Symonds (C-S) and Johnson-Cook (J-C) constitutive models were determined using experimental data. By contrasting the proposed models with the experiment data, the precision of the constitutive models was confirmed.

Short-term vancomycin and buffer soaking does not change rabbit achilles tendon tensile material properties

BackgroundAllograft tendons are commonly used during orthopedic surgery to reconstruct tissue that is severely damaged. Soaking the tendon in an antibiotic solution, specifically vancomycin, has been shown to lower the risk of post-operative infections. While some material properties of tendon and ligament after antibiotic soaking have previously been characterized, extensive sub-failure allograft tendon material properties after soaking in antibiotic solutions have not. MethodsForty tendons were dissected from rabbits and soaked in either a phosphate buffered saline (PBS) only solution or vancomycin and PBS solution for five or 30 min. Immediately after soaking, quasi-static tensile experiments were performed in a materials testing system. FindingsTissue nominal stress, Lagrange strain, toe-region properties and elastic modulus were characterized. For all forty tendons, the average elastic modulus was found to be 455 ± 37 MPa, the average transition strain (from toe-region to linear elastic region) was 0.0487 ± 0.0035, and the average transition stress was 9.71 ± 0.79 MPa. No statistically significant differences in any of these material properties were found across soaking medium or soaking time. InterpretationFrom these results, we conclude that soaking an allograft tendon in antibiotic solution for up to 30 min prior to implantation does not change the tensile material properties of tendons, supporting current clinical practice.

Deformable κ phase induced deformation twins in a CoNiV medium entropy alloy

The degradation of ductility is obvious in low-temperature annealed face centered cubic (FCC) based alloys under bulk quasi-static tensile experiments due to intermetallic phase embrittlement. Here, we demonstrate a novel approach to overcome this loss of deformability by realizing brittle intermetallic phase (κ) shearing and deformation twins in an equiatomic CoNiV medium entropy alloy (MEA) with high stacking fault energy. The brittle κ phase not only contributes to high true ultimate tensile strengths (∼1800→2000 MPa) by shearing, but also enhances the flow stress to approach the critical values for the onset of deformation twins (∼1660-1750 MPa) in this MEA. Such shearing and twins in turn assist further work hardening and strengthening mechanisms that improve the deformability of MEA (uniform elongation ∼25→27%). As a result, the degradation of ductility caused by intermetallic phase embrittlement in this MEA can be recovered. The combination of deformable intermetallic phase and high stress deformation twins proposes a so far untapped strengthening mechanism, for enabling the design of FCC based alloys with improved mechanical properties.

Effects of hygrothermal ageing and temperature on the mechanical behavior of aluminum-CFRP hybrid (riveted/bonded) joints

Hygrothermal ageing and temperature significantly affect the mechanical properties of joints, but the research on their coupling effect in hybrid joints is insufficient. In this work, the combined effects of the long-term factor of hygrothermal ageing and the short-term factor of temperature on the mechanical properties of Al/CFRP hybrid (riveted/bonded) joints (HJs) are investigated by quasi-static tensile experiments and an advanced simulation method. The mechanical properties of HJs with four kinds of ageing degrees are tested at four temperatures (−40 °C, 20 °C, 50 °C, and 80 °C). Experimental results show that the joint strength is mainly affected by temperature, while the breaking elongation is sensitive to the degree of ageing. Although the joint stiffness and strength decrease significantly under the combined action of the increase in temperature and the deepening of the ageing degree, the three-stage characteristics of failure (first, the adhesive bond and the rivet share the load; and then the adhesive bond gradually fractures and loses its load-bearing capacity; finally, the rivet bears the load alone) do not change. Furthermore, by integrating the change information of moisture absorption and Fourier transform infrared spectrum into the material model, the simulation shows new light on the failure mechanisms of the HJs on the coupling effect of temperature and hygrothermal ageing. In conclusion, this research helps deepen the understanding of the changing laws of mechanical behavior of Al/CFRP hybrid joints under actual service conditions.

Influence of Strain History on Dynamic Strain Localization and Stress State During High-Rate Tensile Loading of Titanium Alloys: Experiments, Modeling, and Analytical Methods

Abstract The determination of the mechanical response of engineering materials subjected to high loading rates plays an important role in determining their performance and application. The high strain-rate tensile response of metals is usually investigated by means of the split-Hopkinson tension bar (SHTB) apparatus. The interpretation of the obtained results is, however, subjected to analogous stress and strain uniformity challenges present during quasi-static tensile experiments. Beyond the onset of necking, strains cease to be uniform along the gauge length and localize around the necking zone. Consequently, the nominal strain rate underestimates the effective strain rate experienced by the material. The analysis of the effective strain rate and stress state beyond the onset of necking has received considerable attention in the literature. Several research efforts have focused on the optimization of the geometry of specimens to be employed for the characterization of the dynamic tensile response using the SHTB. The present work investigates, systematically, the effects of strain history and adiabatic heating on the stress state during dynamic loading. A series of monotonic and various strain history experiments were conducted and analyzed. The diameter evolution, effective strain rate, and temperature histories were measured for all conducted experiments. Numerical simulations were carried out to examine the stress state during strain localization and to accurately reproduce engineering and local thermos-mechanical variables. The effectiveness of existing postnecking corrections for high-rate experiments is assessed. A modified postnecking correlation taking into account the effects of adiabatically induced thermal softening is proposed.

Fracture behaviors of long-term low-dose-rate neutron-irradiated Al–Mg–Si alloy

Here, we report on fracture behaviors of Al–Mg–Si alloys (LT21 Al) decommissioned from a research reactor in service for 30 years. Microscopic characterizations show that the initial microstructures of the long-term low-dose-rate neutron-irradiated LT21 Al are dominated by a large number of micrometer-sized voids and second-phase particles, different from short-term high-dose-rate neutron-irradiated materials. Quasi-static tensile and shock spall experiments on the irradiated and unirradiated LT21 Al reveal considerable irradiation-induced softening (larger than 40%) in both the tensile and spall strength. We attribute the irradiation softening to the over-aging process promoted by irradiation enhanced diffusion during the long-term service. Postmortem characterizations on shock-recovered samples indicate that the long-term low-dose-rate neutron irradiation-induced microstructures (micrometer-sized voids and second-phase particles) facilitate nucleation and growth of the dynamic damage in irradiated materials, thus playing an important role in the change in facture behaviors.

High stress twinning in a compositionally complex steel of very high stacking fault energy

Deformation twinning is rarely found in bulk face-centered cubic (FCC) alloys with very high stacking fault energy (SFE) under standard loading conditions. Here, based on results from bulk quasi-static tensile experiments, we report deformation twinning in a micrometer grain-sized compositionally complex steel (CCS) with a very high SFE of ~79 mJ/m2, far above the SFE regime for twinning (<~50 mJ/m2) reported for FCC steels. The dual-nanoprecipitation, enabled by the compositional degrees of freedom, contributes to an ultrahigh true tensile stress up to 1.9 GPa in our CCS. The strengthening effect enhances the flow stress to reach the high critical value for the onset of mechanical twinning. The formation of nanotwins in turn enables further strain hardening and toughening mechanisms that enhance the mechanical performance. The high stress twinning effect introduces a so far untapped strengthening and toughening mechanism, for enabling the design of high SFEs alloys with improved mechanical properties.

Study on the Effect of Salt Solution on Durability of Basalt-Fiber-Reinforced Polymer Joints in High-Temperature Environment.

Due to the low price and good comprehensive properties, FRP composite material has become a new type of civil application material in recent years. In this paper, Araldite® 2012 adhesive was used to bond basalt-fiber-reinforced polymer (BFRP), and the durability of its bonded joints was investigated. Experiments were carried out at 80 °C/DI water (deionized water), 80 °C/3.5% NaCl solution (3.5% SS), and 80 °C/5.0% NaCl solution (5.0% SS) at 0- (unaged), 10-, 20-, and 30-day aging. The specimen and BFRP in the environment of 80 °C/DI water, 80 °C/3.5% SS, and 80 °C/5.0% SS found salt solution under the condition of all sample water absorption decreases, and the activity of salt solution chemistry was weaker compared with deionized water. The load–displacement curve of the joint failure was obtained through quasi-static tensile experiments, and it was found that the adhesive would undergo a post-curing reaction that had a positive impact on the stiffness of the joint in a high-temperature environment. At the same time, it was found that the joint failure strength decreased less in the salt solution environment, and deionized water was more destructive than the salt solution. Referring to the change in water absorption, it was found that the change in the mechanical properties of the joint was mainly related to the permeation effect of the polymer. The change in the Tg of adhesive was measured by differential scanning calorimetry (DSC). It was found that Tg would decrease after aging, and the change in Tg was mainly related to the mobility of the molecular chain. Thermogravimetric analysis (TGA) was used to analyze the thermal behavior of the epoxy resin and some organic matter, and the main weight loss stage was 340–450 °C, which was the complete degradation of epoxy resin and some organic matter. Macro visual and microscopic scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to analyze the failure section, and it can be concluded that the failure mode of joint tear failure transitioned to cohesion in the late–mixed interface failure, at the visible interface between the fiber and the resin matrix.

Influence of Selective Laser Melting Additive Manufacturing Parameters in Inconel 718 Superalloy.

Selective laser melting (SLM) is one of the most reliable and efficient procedures for Metal Additive Manufacturing (AM) due to the capability to produce components with high standards in terms of dimensional accuracy, surface finish, and mechanical behavior. In the past years, the SLM process has been utilized for direct manufacturing of fully functional mechanical parts in various industries, such as aeronautics and automotive. Hence, it is essential to investigate the SLM procedure for the most commonly used metals and alloys. The current paper focuses on the impact of crucial process-related parameters on the final quality of parts constructed with the Inconel 718 superalloy. Utilizing the SLM process and the Inconel 718 powder, several samples were fabricated using various values on critical AM parameters, and their mechanical behavior as well as their surface finish were examined. The investigated parameters were the laser power, the scan speed, the spot size, and their output Volumetric Energy Density (VED), which were applied on each specimen. The feedstock material was inspected using Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) analysis, and Particle-size distribution (PSD) measurements in order to classify the quality of the raw material. The surface roughness of each specimen was evaluated via multi-focus imaging, and the mechanical performance was quantified utilizing quasi-static uniaxial tensile and nanoindentation experiments. Finally, regression-based models were developed in order to interpret the behavior of the AM part’s quality depending on the process-related parameters.

Mechanical Properties of Strengthening 5083-H111 Aluminum Alloy Plates at Elevated Temperatures

The use of aluminum alloys for external strengthening of reinforced concrete (RC) beams has been capturing research interest. Exposure to harsh environmental conditions can severely impact the strengthening efficiency. This works aims to investigate the degradation in the mechanical properties of aluminum alloy AA 5083 plates when exposed to temperatures ranging from 25 to 300 °C. Quasi-static Isothermal tensile experiments were conducted at different temperatures. It was observed from the experimental results that the yield strength remained constant in the temperature range of 25–150 °C before starting to drop beyond 150 °C, with a total reduction of ≈ 40% at 300 °C. The elastic modulus was temperature sensitive with about 25% reduction at 200 °C before experiencing a significant and pronounced reduction at 300 °C. The percentage drops in stiffness and yield strength at 300 °C were 62.8% and 38%, respectively. In addition, the Mechanical Threshold Strength Model (MTS) parameters were established to capture the yield strength temperature dependence. Two analytical models were developed based on the experimental results. Both models can reasonably predict the elastic modulus and yield strength of AA 5083 plates as a function of temperature. It was concluded that AA plates should be properly insulated when used as externally bonded reinforcement to strengthen RC beams.

Atomistically informed crystal plasticity analysis of deformation behavior of alloy 690 including grain boundary effects

In this paper, we predict the deformation behavior of alloy 690 by explicitly modeling finite thickness grain boundaries within the crystal plasticity framework. This is realized by using a blend of quasi-static tensile experiments, microstructural characterization using scanning electron microscopy, atomistic simulations and crystal plasticity finite element analysis. We begin with material characterization to probe the type of grain boundaries present in the Ni-based alloy 690. Inspired by physically justified multiscale modeling schemes, we then use atomistic simulations within the framework of embedded-atom method to quantify activation parameters for dislocation nucleation from those grain boundaries in Ni bicrystals. The kinetic activation parameters are then passed on to a transition state theory based crystal plasticity model. At this scale, the grain boundaries are explicitly modeled using finite elements and prescribed distinct constitutive parameters obtained from lower scale atomistic simulations. The predictive capabilities of the adopted methodology are demonstrated by capturing the uniaxial tensile behavior of alloy 690 at different temperatures (250C–6000C) (stress-strain curves as well as texture evolution). Our implementation of grain boundaries in crystal plasticity is built upon a standard representative volume element used in most polycrystalline simulations. It is envisioned that this comprehensible approach will provide a compelling platform for unifying many other interface related deformation processes at the mesoscale. Eventually, the demonstrated methodology can expedite in apprehending the structure-property relationships through apt use of physically justified multiscale modeling schemes.

Research in failure behaviors of hybrid single lap aluminum-CFRP (plain woven) joints

In this paper, the failure behaviors of the hybrid joint (HJ) of plain woven carbon fiber reinforced plastic (CFRP) and aluminum alloy were systematically studied by quasi-static tensile experiments and a new refined simulation. Experimental results showed that the HJ failure has a typical three-stage feature: first, the bond line and the rivet share the load; and then the bond line gradually fractures; finally, the rivet bears the load alone. It is also concluded that HJs are superior to bonded joints and riveted joints in strength and energy absorption. As for the simulation model, a damage mechanics model considering shear nonlinearity and distinguishing failure modes for plain woven CFRP was constructed, added with a cohesive behavior for the bond line and a bilinear elastoplastic hardening model for the aluminum alloy substrate and the stainless steel rivet. Based on the simulation model, the three-stage feature was successfully simulated. Furthermore, the simulation results shed new light on the failure mechanisms of the HJs as well as the influences of clamping force and interference-fit on the HJ mechanical properties. In conclusion, this research helps to understand the failure behaviors and provides guidance for the design and manufacture of HJs.

Process-structure-property relations for as-deposited solid-state additively manufactured high-strength aluminum alloy

Solid-state additive manufacturing methods provide innovative solutions to circumvent problems associated with materials susceptible to hot cracking by avoiding liquid solid phase transformations. In this work, the process parameter influence on microstructural evolution and mechanical response of a fully dense aluminum alloy 7050 (AA7050) component manufactured via a rapid, solid-state additive manufacturing process known as Additive Friction Stir Deposition (AFS-D) was quantified for the first time. Three sections (starting dwell, transient, crossover of roads) of the deposition that exhibit differing thermomechanical processing histories were evaluated for the resulting microstructure and mechanical response. The microstructural characterization was performed on the as-deposited AA7050 via Electron Backscatter Diffraction (EBSD), Transmission electron microscopy (TEM), optical microscopy, and Scanning Electron Microscopy (SEM). The microstructural characterization revealed refined constituent particles and grains throughout the as-deposited AA7050 microstructure. Furthermore, quasi-static tensile experiments were conducted in both the build and transverse directions, in order to quantify the orientation influence on tensile properties of the as-deposited AA7050 build. Spatially dependent tensile properties were observed in the material due to heat input variation coarsening of secondary phases towards the initial layers of the AFS-D build. Post-mortem analysis revealed that voids nucleated and coalesced from the overgrowth of the strengthening precipitates present in the material, resulting in fracture.