Quasi-static Mechanical Tests Research Articles

Investigation of Bimodal Aluminium Matrix Syntactic Foams Filled with Ceramic Hollow Spheres

Abstract In this study bimodal A413 matrix syntactic foams filled with ceramic hollow spheres (CHSs) were produced and examined by computer tomography (CT) and quasi-static mechanical testing to determine the mixing properties of the hollow spheres and the strength of the metal foam. Two hollow spheres of different nominal diameters (d1 = 2.4 mm and d2 = 7.0 mm) were used in equal volume ratio. The produced metal foams have a density of 1.61±0.03 g/cm3, with smaller inclusions and some defective hollow spheres in the structure. The foams have an average compressive strength of 120 MPa and a specific mechanical energy absorbing capacity of 43.5 J/cm3. As a result of the upsetting tests, the matrix material is separated from the CHSs, breaking the connection between them.

Low-temperature effect on the impact and flexural behaviour of basalt composite laminates

Epoxy based laminates reinforced with woven basalt fibres have been manufactured and characterized by quasi-static mechanical tests and low-velocity impact tests. Samples were prepared by infusion of 16 plies of basalt under pre-optimized conditions. All the interlaminar shear strength, flexural and impact tests were carried out at room temperature, −25 °C and −50 °C to investigate the effect of temperature on the mechanical characteristics and the impact damage onset and propagation. Ultrasonic technique were adopted to provide information on the shape and the extent of the internal damage. The final aim was to be able to predict impact energy and delamination under different temperature conditions and to assess the influence of the resin matrix stiffening at low temperature on the composite behaviour. Results show that at low temperature due to the stiffening of the resin matrix, the composite tested is more resistant and less deformable. It is interesting since, at low temperatures, it is more straightforward the damage propagation. In particular, ILSS and flexural tests show a maximum increase of 39% and 12.78% respectively at T = −50 °C compared to the value at room temperature. A delamination area increase of wholly 40% at T = −50 °C, is detected.

Effect of the temperature and strain rate on the tension response of uncured rubber: Experiments and modeling

The temperature and strain rate dependence of the tensile behaviors of uncured carbon black-filled rubber are investigated through quasi-static mechanical tests under different loading scenarios. The significant influences of both the temperature and strain rate on the distinct deformation characteristics (hysteresis, stress level at a certain stretch, and the Mullins effect) during the tensile process are systematically discussed and explained microscopically. An interpretation of the underlying physical mechanisms of uncured carbon black filled rubber is proposed, which is similar to that of vulcanized rubber. Based on this interpretation, a thermomechanical constitutive model is developed to represent the complex constitutive behaviors of uncured rubber. Using this new model, the distinct characteristics of the cyclic tests can be accurately captured over a wide range of temperatures and strain rates. Moreover, the experimental fitting results under selected working conditions can effectively predict the other experimental results.

Fracture mechanism and model of 18Ni maraging steel

ABSTRACT18Ni maraging steel is normally used to make key components by machining processes. It is necessary to understand the fracture mechanism and behaviour of 18Ni maraging steel for the study and further optimisation of machining processes. In this paper, the Split Hopkinson Tensile Bar tests accompanied by quasi-static mechanical tests are carried out to relate the stress triaxiality, deformation temperature and strain rate with the fracture strain. During the building up of the fracture model, it is noticed that the change of fracture mechanism from 600°C to 900°C brings about a non-linear relationship of fracture strain with the deformation temperature. This results in a large error in fitting the Johnson–Cook (J-C) fracture model, so a modified fracture model is put forward.

Femur strength predictions by nonlinear homogenized voxel finite element models reflect the microarchitecture of the femoral neck

In the human femoral neck, the contribution of the cortical and trabecular architecture to mechanical strength is known to depend on the load direction.In this work, we investigate if QCT-derived homogenized voxel finite element (hvFE) simulations of varying hip loading conditions can be used to study the architecture of the femoral neck. The strength of 19 pairs of human femora was measured ex vivo using nonlinear hvFE models derived from high-resolution peripheral QCT scans (voxel size: 30.3 µm). Standing and side-backwards falling loads were modeled. Quasi-static mechanical tests were performed on 20 bones for comparison. Associations of femur strength with volumetric bone mineral density (vBMD) or microstructural parameters of the femoral neck obtained from high-resolution QCT were compared between mechanical tests and simulations and between standing and falling loads.Proximal femur strength predictions by hvFE models were positively associated with the vBMD of the femoral neck (R² > 0.61, p < 0.001), as well as with its cortical thickness (R² > 0.27, p < 0.001), trabecular bone volume fraction (R² = 0.42, p < 0.001) and with the first two principal components of the femoral neck architecture (R² > 0.38, p < 0.001). Associations between femur strength and femoral neck microarchitecture were stronger for one-legged standing than for side-backwards falling. For both loading directions, associations between structural parameters and femur strength from hvFE models were in good agreement with those from mechanical tests. This suggests that hvFE models can reflect the load-direction-specific contribution of the femoral neck microarchitecture to femur strength.

Microstructure and mechanical properties of an alpha keratin bovine hoof wall

Bovine hoof wall with an alpha keratin structure, as the interface between the ground and the body, can protect the bony skeleton from the impact and the destruction. Microstructure and mechanical properties of the bovine hoof wall are investigated by scanning electron microscope (SEM), transmission electron microscope (TEM) and quasi-static mechanical tests. Mechanical results show that the mean J-integral values of the LD specimens parallel to the tubular axis are higher than those of the TD specimens normal to the tubular axis, and the fracture toughness reaches the peak values (21 kJ/m2, 33 kJ/m2 for the TD and the LD specimens, respectively) at 16.5% moisture content. The morphology results show that the laminated keratin structure can form the extensive strain-transition interfaces and the tubules played an important role in twisting crack propagation. Angles of the laminated structures within the inter-tubular materials are not a uniform distribution varying from 0° to 90° against to the tubular axis. The interlocking interface in the tubular structure can provide increased the contact area and contribute to the bonding strength between the layers. We also propose models to illustrate the morphological structure and the crack propagation mechanism of the bovine hoof wall. This structure with the strong fracture resistance ability will provide a new inspiration for design of structural materials and architectures.

Mechanical Properties of Remote-Laser Cut CFRP and Thermographic Laser-Process Monitoring

Remote-laser beam cutting is a productive technology without tool wear. Especially when cutting carbon fiber reinforced polymers (CFRP), it offers constant manufacturing quality. Since it is a thermal process, a heat-affected zone (HAZ) is formed at the edge of the cut. Based on quasi-static and cyclic mechanical tests on open-hole specimens, the influence of the process on the mechanical properties of CFRP is shown. The quasi-static tests are in good correlation with results from other researchers by indicating an increase in the maximum tensile stress of the test specimens, cut by remote-laser. The reason is the rearrangement of the shear stresses and a reduction of the notch stress concentration. However, the results of the present study show that excessive expansion of the HAZ leads to a reduction in the maximum tensile stress compared to milled test specimens. Under cyclic load conditions, remote-laser beam cutting does not lead to a more pronounced degradation than milling. The mechanical properties of the notched test pieces are sensitive to the expansion of the HAZ. For the production of components it is therefore necessary that the remote-laser beam cutting is carried out under controlled and documentable conditions. For this purpose, process thermography was tested as a tool for quality assurance. The results show that the technology is basically suitable for this task.

Comparison of elastic properties of low-density polymeric foams determined by ultrasonic wave propagation and quasi-static mechanical testing

The ability to predict the mechanical performance of materials without sample extraction is of great interest to manufacturers and end-users. The aim of this work was to examine the relationship between the quasi-static measurements (i.e. the typically reported elastic property) and the non-destructive in-line in-situ ultrasonic wave propagation-derived elastic moduli of porous polyurethane foams over a range of densities. It was found that the ratio of moduli was direction-dependent: a factor of 2 when the testing was perpendicular to the pore orientation and a factor of 1.7 when parallel to the pore rising direction. The deviation was explained by ruling mechanisms such as strain rate and amplitude, deviation from orthotropic theory and anisotropy, and degree of density which affected shear wave propagation. The correlations were in agreement with those reported for other porous materials. The quantification of this correlation is a practical tool for estimating elastic properties on heterogeneous, irregularly shaped samples not suitable for bulk testing, or for in-line rapid quality control of parts in production lines.

Comparing the fracture limits of the proximal femur under impact and quasi-static conditions in simulation of a sideways fall

Sideways falls onto the hip are responsible for a great number of fractures in older adults. One of the possible ways to prevent these fractures is through early identification of people at greatest risk so that preventive measures can be properly implemented. Many numerical techniques that are designed to predict the femur fracture risk are validated through performing quasi-static (QS) mechanical tests on isolated cadaveric femurs, whereas the real hip fracture is a result of an impact (IM) incident. The goal of this study was to compare the fracture limits of the proximal femur under IM and QS conditions in the simulation of a sideways fall to identify any possible relationship between them.Eight pairs of fresh frozen cadaveric femurs were divided into two groups of QS and IM (left and right randomized). All femurs were scanned with a Hologic DXA scanner and then cut and potted in a cylindrical tube. To measure the stiffness in two conditions of the single-leg stance (SLS) and sideways fall (SWF), non-destructive tests at a QS displacement rate were performed on the two groups. For the destructive tests, the QS group was tested in SWF configuration with the rate of 0.017 mm/s using a material testing machine, and the IM group was tested in the same configuration inside a pneumatic IM device with the projectile target displacement rate of 3 m/s.One of the IM specimens was excluded due to multiple strikes. The result of this study showed that there were no significant differences in the SLS and SWF stiffnesses between the two groups (P = 0.15 and P = 0.64, respectively). The destructive test results indicated that there was a significant difference in the fracture loads of the two groups (P < 0.00001) with the impact ones being higher; however, they were moderately correlated (R2 = 0.45). Also, the comparison of the fracture location showed a qualitatively good agreement between the two groups.Using the relationship developed herein, results from another study were extrapolated with errors of less than 12%, showing that meaningful predictions for the impact scenario can be made based on the quasi-static tests. The result of this study suggests that there is a potential to replace IM tests with QS displacement rate tests, and this will provide important information that can be used for future studies evaluating clinical factors related to fracture risk.

Low-velocity impact response of friction riveted joints for aircraft application

In this paper, the sensitivity of carbon fiber reinforced polyether-ether-ketone (CF-PEEK) friction riveted joints to impact damage was assessed as well as the damage propagation during fatigue and quasi-static mechanical testing. The joints were impacted with energies between 5 J and 30 J at room temperature and the impact damage was evaluated through microscopy and ultrasonic C-scan. Two damage types were identified: barely-visible impact damage with mainly shear-driven damage in the first plies of the composite and visible impact damage with delamination and premature failure of the rivet-composite interface owing to peel stresses upon the impact event. The joint strength and fatigue life were not compromised by the barely-visible impact damage, while a 40% decrease of quasi-static strength and lower fatigue resistance were achieved for visible impact damage. Despite altered fatigue behavior of impacted joints, damage accumulated towards fatigue was not critical to the joint mechanical integrity, confirmed by the residual strength of up to 96% after 106 cycles for 20 J impacts.

Improved constitutive model of the jellyroll for cylindrical lithium ion batteries considering microscopic damage

The stiffness of Li-ion batteries is defined as the derivative of force with respect to displacement. The existing constitutive models of the jellyroll of Li-ion batteries reveal that such stiffness keeps increasing as displacement increases. In this study, quasi-static mechanical abusive tests are performed on 18650 cylindrical Li-ion batteries at different state of charge. The experimental results indicate that three distinct stages are identified in the stiffness curve corresponding to densification stage, microscopic damage stage and macroscopic failure stage, and the stiffness only increases in the first stage and decreases in the latter two stages. Therefore, this paper proposes the improved constitutive model of the jellyroll of Li-ion batteries to describe their kinematics considering microscopic damage. An explicit finite element model of a Li-ion battery is established to validate the improved constitutive model. The voltages and temperatures of Li-ion batteries are also recorded to reveal their responses at different stages. It is found that Li-ion batteries at the fully charged state initiate internal short circuit before the end of the stage 2 (microscopic damage stage) whereas Li-ion batteries at low state of charge will only initiate internal short circuit at the stage 3 (macroscopic failure stage).

Mechanical response and crack propagation of oil well cement under dynamic and static loads

The dynamic mechanical properties and fracture mechanism of three types of oil well cement with different formulations were investigated using a Φ50 mm split Hopkinson pressure bar (SHPB) and quasi-static mechanical tests were conducted with a hydraulic universal testing machine. The stress-strain diagram, time-stress diagram, total energy absorption diagram, and the dynamic growth factor (DIF) under different strain rates were obtained. The crack propagation process of the oil well cement under dynamic loading is evaluated using high-speed photography to determine the fracture mechanism. The test results show that the strength of the cement increases under a dynamic impact. The compressive strength of the pure cement increases from 37 MPa to 184.80 MPa under static loading. However, the peak stress of the cement stone strengthened with cellulose fiber is lower under a dynamic load than a static load. Under dynamic loading, the absorption energy is higher for the pure cement stone than for the cement stone reinforced with whiskers and cellulose. Furthermore, the crack initiation, crack propagation, and fracture characteristics of the oil well cement are different under dynamic and static loads. Under a static load, the rupture of the cement is the result of the propagation of the tensile cracks. Under dynamic loading, there are fewer micro cracks on the cement surface and a composite fracture results from tensile and shear cracks.

Quasi-static and dynamic response of oriented strand boards based on balsa wood waste

This work presents an evaluation of the performance of Oriented Strand Boards (OSB) panels based on balsa wood (Ochroma Pyramidale) waste agglomerated with castor oil polyurethane resin. In this study, were evaluated OSB panels with different densities (300 kg/m3, 400 kg/m3 and 650 kg/m3), with 10 mm thickness and castor oil polyurethane resin in different contents (11% and 15%). The OSB panels were preliminary characterized by physical and quasi-static mechanical tests to identify the class of application of this material according to the recommendations of standard EN 300: 2002. Subsequently, the OSB panels were characterized by low velocity impact tests. Panels with the highest density outperformed those with the lowest one in terms of peak force and perforation energy (Ep = 22.88 J). Both properties are clearly influenced by the better compaction of the particles, as confirmed by the higher value of internal adhesion (0.46 MPa), which resulted also in better residual flexural properties after impact, with a reduction in strength of 36% for the samples with 650 kg/m3 compared to about 70% for the samples with the lowest density at an impact energy level equal to 50% of the respective perforation energy.

Characterization of elastomeric scaffolds developed for tissue engineering applications by compression and nanoindentation tests, μ-Raman and μ-Brillouin spectroscopies.

In tissue engineering, porous biodegradable scaffolds are developed with morphological, chemical and mechanical properties to promote cell response. Therefore, the scaffold characterization at a (sub)micrometer and (bio)molecular level is paramount since cells are sensitive to the chemical signals, the rigidity, and the spatial structuring of their microenvironment. In addition to the analysis at room temperature by conventional quasi-static (0.1-45 Hz) mechanical tests, the ultrasonic (10 MHz) and μ-Brillouin inelastic light scattering (13 GHz) were used in this study to assess the dynamical viscoelastic parameters at different frequencies of elastomeric scaffolds. Time-temperature superposition principle was used to increase the high frequency interval (100 MHz-100 THz) of Brillouin experiments providing a mean to analyse the viscoelastic behavior with the fractional derivative viscoelastic model. Moreover, the μ-Raman analysis carried out simultaneously during the μ-Brillouin experiment, gave the local chemical composition.

A new noninvasive mechanical bending test accurately predicts ulna bending strength in cadaveric human arms.

High error rates in the prediction of fragility fractures by bone mineral density have motivated searches for better clinical indicators of bone strength, and the high incidence of non-hip, non-spine fractures has raised interest in cortical bone. The aim of this study was to assess the accuracy of Cortical Bone Mechanics Technology™. CBMT is a new non-invasive 3-point bending technique for measuring the mechanical properties of cortical bone in the ulnas of living humans. 35 cadaveric human arms were obtained from small women and large men ranging widely in age (17 < Age < 99 years) and body size (14 < BMI < 40 kg/m2). Noninvasive CBMT measurements of the flexural rigidity of the ulna bones within these arms (EICBMT) were compared to measurements of EI by Quasistatic Mechanical Testing in the ulnas excised from those arms (EIQMT). Ulna bending strength was also measured by QMT as the peak moment before fracture (Mpeak). The open source BoneJ plugin to ImageJ image processing software was used to calculate cortical porosity (CP) in micro-computed tomography images of a 2 mm length of the mid-shaft of each fractured ulna, and the interosseous diameter (IOD) of each ulna was also measured in those images. EICBMT measurements (13 < EICBMT < 97 Nm2) explained 99% of the variance in QMT measurements of ulna bending strength (11 < Mpeak < 90 Nm), but EICBMT was biased high by 30% (p < 0.0001) relative to EIQMT (11 < EIQMT < 69 Nm2). After correcting this bias, EICBMT and EIQMT measurements lay along the identity line (y = 1.00x, R2 = 0.99, SEE = 3.1 Nm2). Predictions of Mpeak by EICBMT were less accurate than predictions by EIQMT (both R2 = 0.99; SEECBMT = 5.9 Nm vs SEEQMT = 4.5 Nm, F = 2.92, p = 0.001), but EICBMT predictions were substantially more accurate than those by IOD (R2 = 0.79; SEEIOD = 10.6 Nm, F = 3.30, p < 0.001) and CP (R2 = 0.35; SEECP = 18.9 Nm, F = 10.45, p < 10-9). Predictions by EICBMT were also more accurate than predictions by arm donor height (R2 = 0.63; SEE = 14.3 Nm, F = 5.87, p < 10-6), body weight (R2 = 0.77; SEE = 11.1 Nm, F = 3.54, p < 0.001) and BMI (R2 = 0.64; SEE = 14.1 Nm, F = 2.39, p < 0.01). In forward stepwise multiple regression beginning with EICBMT, only age explained any additional variance in ulna bending strength (ΔR2 = 0.3%, F = 8.03, p = 0.008). Noninvasive CBMT measurements of ulna EI explain 99% of individual differences in QMT measurements of ulna bending strength in cadaveric human arms.

Dynamic Loading of Lattice Structure Made by Selective Laser Melting-Numerical Model with Substitution of Geometrical Imperfections.

Selective laser melting (SLM) is an additive technology that allows for the production of precisely designed complex structures for energy absorbing applications from a wide range of metallic materials. Geometrical imperfections of the SLM fabricated lattice structures, which form one of the many thin struts, can lead to a great difference in prediction of their behavior. This article deals with the prediction of lattice structure mechanical properties under dynamic loading using finite element method (FEA) with inclusion of geometrical imperfections of the SLM process. Such properties are necessary to know especially for the application of SLM fabricated lattice structures in automotive or aerospace industries. Four types of specimens from AlSi10Mg alloy powder material were manufactured using SLM for quasi-static mechanical testing and determination of lattice structure mechanical properties for the FEA material model, for optical measurement of geometrical accuracy, and for low-velocity impact testing using the impact tester with a flat indenter. Geometries of struts with elliptical and circular cross-sections were identified and tested using FEA. The results showed that, in the case of elliptical cross-section, a significantly better match was found (2% error in the Fmax) with the low-velocity impact experiments during the whole deformation process compared to the circular cross-section. The FEA numerical model will be used for future testing of geometry changes and its effect on mechanical properties.

Mechanical and electrical response of cylindrical Lithium-ion cells at various State of Charge

Recent evidence has shown that the mechanical properties of lithium-ion battery will change with the change of State of Charge (SOC) value. In this investigation, several quasi-static mechanical tests on 18650 battery cells with various SOC values were performed to reveal the SOC dependent mechanical behaviors and the voltage response of Lithium-ion battery. Experimental results indicate that the ability of Lithium-ion battery to resist deformation will increase with SOC value increasing. An explicit finite element model was established in HyperWorks/LS-DYNA with taking SOC effect into account.

Effect of surrogate design on the measured stiffness of snowboarding wrist protectors

In snowboarding, the wrist is the most common injury site, as snowboarders often put their arms out to cushion a fall. This can result in a compressive load through the carpals coupled with wrist hyperextension, leading to ligament sprains or carpal and forearm bone fractures. Wrist protectors are worn by snowboarders in an effort to reduce injury risk, by decreasing peak impact forces and limiting wrist extension to prevent hyperextension during falls. There is no international standard or universally accepted performance specification that snowboarding wrist protectors should conform to, resulting in an inability to judge which designs offer the best protection. This study investigated how surrogate arm design affected the stiffness of wrist protectors during quasi-static mechanical testing. Three surrogate arms with increasing design complexity were used to test three wrist protectors. The results show that surrogate design does influence the stiffness of snowboarding wrist protectors. Given that the surrogate does influence protector performance, it is recommended that a standard surrogate design is established for research and product testing.

A mechanical reduced order model for elastomeric 3D printed architectures

Abstract

State of Charge Dependent Constitutive Model of the Jellyroll of Cylindrical Lithium-Ion Cells

Most literature on the mechanical properties of Lithium-ion battery cells is concerned with the mechanical behavior of jellyroll or Lithium-ion battery when the state of charge (SOC) is 0%. Recent evidence shows that the mechanical properties of Lithium-ion batteries change as the SOC value changes. In this paper, several quasi-static mechanical tests on 18650 battery cells with various SOC values are performed to reveal the SOC-dependent mechanical and electrochemical failure behavior of Lithium-ion batteries. The SOC-dependent constitutive model of the jellyroll is proposed. Experimental results indicate that the ability of Lithium-ion batteries to resist deformation increase as the SOC value increases. An increase in the SOC value may facilitate thermal runaway after an internal short circuit. An explicit finite-element model of a Lithium-ion battery is established to validate the proposed approach. The simulation results of various loading cases are in good agreement with the corresponding experimental results. The established SOC-dependent finite-element model of a Lithium-ion battery may be beneficial to produce accurate simulations of an entire battery pack during operation.