Biaxial Testing Machine Research Articles

Multiaxial creep deformation investigation of miniature cruciform specimen for type 304 stainless steel at 923 K using non-contact displacement-measuring method

Abstract Multiaxial creep investigations at high temperatures are required to guarantee the integrity of structural materials such as boiler pipes for power generation and turbine blades for aviation and industrial applications. The multiaxial creep testing method using a cruciform specimen has several advantages, and the authors successfully downsized the specimen. The authors also developed a technique for the in situ observation of the specimen in an electric furnace and the non-contact displacement measurement in the development of a biaxial tensile creep testing machine for the miniature cruciform specimen. By observing the specimen at a target mark during the creep testing through an observation window installed at the bottom of the furnace, it was possible to visualize the specimen surface variations and obtain the axial strain from the locus of the target marks. The Mises-type equivalent strain was calculated from the axial strains obtained in the equi-biaxial tensile multiaxial creep testing and was compared with the strains obtained in the uniaxial creep testing. The Mises-type equivalent strain can be expressed using a unified method up to approximately 5% of the initial strain in the test, even in the multiaxial stress state.

Effect of symmetrical biaxial tension on the magnetic properties of the composite specimen of two steel plates with different mechanical and magnetic properties

The results of studying the behavior of the magnetic characteristics of two-layer material containing layers of annealed sheet low-carbon Steel 15 and sheet metastable austenitic 12Kh18N9Т steel, subjected to cold rolling with a compression of 50 %, under biaxial symmetric tension have been presented. Experiments on biaxial deformation were carried out on the original biaxial testing machine, allowed to determine the physical properties of materials during elastic-plastic deformation independently along two axes. It has been shown that the coercive force of the studied two-layer material vary monotonically over the entire range of elastic-plastic biaxial deformation and can be used as an informative parameter for assessing the it’s stresses and deformations.

Horizontal Test Stand for Bone Screw Insertion

Screws are a versatile method of fixation and are often used in orthopaedic surgery. Various specialised geometries are often used for bone screws to optimise their fixation strengths in limited spaces at the expense of manufacturing costs. Additionally, ongoing research is looking to develop systems/models to automatically optimise bone screw tightening torques. For both applications, it is desirable to have a test rig for inserting screws in a regulated, instrumented, and repeatable manner. This work presents such a test rig primarily used for the validation of optimal torque models; however, other applications like the above are easily foreseeable. Key features include controllable insertion velocity profiles, and a high rate measurement of screw torque, angular displacement, and linear displacement. The test rig is constructed from mostly inexpensive components, with the primary costs being the rotational torque sensor (approx. 2000 €), and the remainder being approximately 1000 €. This is in comparison to a biaxial universal testing machine which may exceed 100,000 €. Additionally, the firmware and interface software are designed to be easily extendable. The angular velocity profiling and linear measurement repeatability of the test rig is tested and the torque readings are compared to an off-the-shelf static torque sensor.

Investigation on the biaxial tensile testing method for metal foil using cruciform specimen

The assessment of mechanical properties of metal foil under complicated stress states poses a considerable challenge, requiring the development of new testing methods and the optimization of new specimen geometry. In this research, the biaxial tensile method and specimen shape were designed and optimized by using simulation and experiment. It is determined that the strain measurement area can be suggested as the central area of 0.6 to 0.8 times the arm width. The influence of different parameters on the tensile results of cruciform specimens was comprehensively evaluated by finite element method and multi-factor analysis. The results indicate that the number of slits markedly impacts the stress–strain uniformity and shear stress in the central region, followed by the slit length. The effect of the arm width and the slit width is comparable, more influential than the corner radius. According to the analyzed results and application requirements, a four-axis independently driven biaxial tensile test machine for small scale samples was fabricated. During the biaxial tension, the center point offset of the specimen remains within ±0.01 mm. The displacement and load synchronization errors do not exceed 0.01 mm and 50 N, respectively, facilitating the precise control of four-axis synchronization. Conclusively, cruciform specimens featuring diverse geometric characteristics were designed for industrial pure titanium, 304 stainless steel, and Inconel 718 superalloy with thickness of less than 0.3 mm. The biaxial tensile tests were performed to delineate the yield loci, revealing notable anisotropy and size effect. The validation confirms the suitability of the testing method and optimized cruciform specimens for conducting biaxial tensile mechanical properties testing on metal foils characterized by diverse types and thicknesses.

Test Setup for Investigating the Impact Behavior of Biaxially Prestressed Composite Laminates

Instrumented impact testing and compression-after-impact testing are important to adequately qualify material behavior and safely design composite structures. However, the stresses to which fiber-reinforced plastic components are typically subjected in practice are not considered in the impact test methods recommended in guidelines or standards. In this paper, a test setup for investigating the impact behavior of composite specimens under plane uniaxial and biaxial preloading is presented. For this purpose, a special test setup consisting of a biaxial testing machine and a specially designed drop-weight tower was developed. The design decisions were derived from existing guidelines and standards with the aim of inducing barely visible impact damage in laminated carbon fiber-reinforced plastic specimens. Several measurement systems have been integrated into the setup to allow comprehensive observation of the impact event and specimen behavior. A feasibility test was performed with biaxially prestressed carbon fiber-reinforced plastic specimens in comparison with unstressed reference tests. The compressive-tensile prestressing resulted in lower maximum contact forces, higher maximum deflections, higher residual deflections and a different damage pattern, which was investigated by light microscopic analysis. Finally, the functionality of the experimental setup is discussed, and the results seem to indicate that the test setup and parameters were properly chosen to investigate the effect of prestresses on the impacts behavior of composite structures, in particular for barely visible subsequent damages.

Warp-knitted strain sensors: impact of loop parameters on sensing performance under biaxial stretching

This paper explores the sensing performance displayed by warp-knitted strain sensors under biaxial stretching. These sensors were knitted using silver-plated nylon to be interlooped on a tricot warp-knitting machine. Eight types of warp-knitted sensing fabrics with different loop parameters were prepared and, afterward, electro-mechanical tests were conducted on a biaxial tensile testing machine. These specimens offered similar ground structures but differed in conductive yarn configuration in terms of linear density, number of underlapping wales, open/closed loop type, and guide-bar lapping sequence. Experimental results showed that the loop parameters significantly played a fundamental role in determining sensing performance. It is therefore possible to improve the sensing performance of warp-knitted sensors and engineer them by differing the loop parameters based on certain applications.

Low-temperature friction experiments on ice–salt mixtures: Implications for the strength of ice plate boundaries on Europa

While recent observational studies have suggested that the ice shell on Europa is undergoing active plate subduction, some theoretical studies have concluded that the high frictional strength of ice would prevent such icy plates from subducting. Constraining the frictional behavior of mixtures of ice and non-ice materials that exist on the surface is therefore key to understanding the frictional strength of plate boundaries on Europa. Here we perform friction experiments on 1 mm thick layers of gouge comprised of mixtures of ice-Ih and magnesium chloride with 0, 17, 29.5 and 47 wt% salt under low-temperature conditions (−40 to −10 °C). The experiments are conducted using a biaxial testing machine with constant normal stresses of either 2.5 or 5.0 MPa, and a constant shear velocity of 3 μm/s. Our experimental results for pure ice and ice–salt mixtures yield steady-state friction coefficients ranging from 0.72 ± 0.02 (−39.2 ± 0.7 °C) to 0.47 ± 0.01 (−16.4 ± 0.2 °C), and 0.51 ± 0.01 (−39.8 ± 1.4 °C) to 0.10 ± 0.02 (−16.9 ± 0.5 °C), respectively. These differences in friction coefficient indicate that non-ice materials can have a significant effect on the friction coefficient along the plate boundaries on Europa. Spatial variations in the frictional strength of plate boundaries are expected to be localized near the base of the conductive layer, as the friction coefficient of the ice–salt mixture exhibits a strong temperature dependence. The observed stick–slip behavior at low temperatures in our experiments indicates the potential for occurrence of intermittent stick–slip along the shallower parts of the plate boundaries, whereas steady-state sliding occurs along the deeper parts.

Effect of elastic-plastic deformation by biaxial tension on the magnetic characteristics of the nickel

The studies were carried out in a test facility based on the original biaxial testing machine created at the IES UB RAS, designed to determine the physical properties of materials during elastic-plastic deformation independently along two axes. Finite element modeling of the stress-strain state of a cruciform nickel specimen has shown that, under symmetric biaxial tension, equivalent von Mises stresses are uniformly distributed in the central part. The results of microstructural studies indicate that dynamic recrystallization takes place in the material during biaxial deformation at room temperature. The results of studying the behavior of the hysteretic magnetic characteristics, magnetostriction, Barkhausen magnetic noise parameters, and electromagnetic parameters of nickel under biaxial symmetrical tension have been presented. A unique relationship between the coercive force and equivalent stresses in the region of plastic deformation has been revealed. It has been shown that such magnetic parameters as maximum magnetic permeability and the maximum in the field dependence of differential magnetic permeability, as well as the amplitude and frequency of the eddy current signal determined at a frequency of 10 kHz, vary monotonically with increasing equivalent stresses under both elastic and plastic deformations.

Laser induced high temperature thermal-mechanical-oxygen coupling experimental system and method

In this paper, a thermal–mechanical–oxidation coupling experimental system based on laser heating is developed, containing two modes of Gaussian and flat-top lasers, which has a series of advantages such as high temperature range, rapid heating rate, and convenient observation. The system adopts active illumination and an optical filter to solve the problem where it is difficult for traditional digital-image correlation technology to image clearly under laser heating. A biaxial mechanical test machine is used to simulate the complex load by applying biaxial tension or compression loads on the material. Combined with the radiation temperature measurement and controllable flow field device, the thermal-mechanical-oxygen coupling experiment of high temperature resistant materials under aerobic environment can be carried out. The maximum uniform heat flux output density is 27.2 kW/cm2, and the maximum Gaussian heat flux output density is 105 kW/cm2. The thermal-mechanical-oxygen coupling experimental system and method are of great significance to the development of new high temperature resistant materials and thermal barrier coatings.

Effects of Lateral Opening-Wedge Distal Femoral Osteotomy on Meniscal Allograft Transplantation: A Biomechanical Evaluation

Background: Lateral meniscal deficiency with valgus malalignment increases the rate of lateral compartment osteoarthritis. Lateral meniscal allograft transplantation (LMAT) with a concomitant varus-producing opening-wedge distal femoral osteotomy (DFO) is an option yet to be evaluated biomechanically. Purpose/Hypothesis: The purpose of this study was to clarify the biomechanical effects of the realignment procedure in the setting of LMAT. We hypothesized that (1) given the dependence of the lateral compartment on the lateral meniscus, a DFO and increasing degrees of varus would be insufficient to restore lateral compartment pressures to normal from a lateral meniscus-deficient state, and that (2) LMAT would restore lateral compartment pressures to the intact state while DFO would decrease lateral compartment pressures for any given state of the meniscus. Study Design: Controlled laboratory study. Methods: Ten cadaveric knees underwent opening-wedge varus-producing DFO secured by an external fixator. Anatomic alignment was standardized to 6° of mechanical valgus, and each joint was tested in full extension. Submeniscal placement of thin film pressure sensors allowed for the recording of contact pressure, peak contact pressure, and contact area. The specimens were loaded on a biaxial dynamic testing machine with loading angles between 9° valgus and 6° varus of mechanical alignment. Conditions tested included intact meniscus, meniscal deficiency, and meniscal transplantation. Results: Isolated varus-producing DFO to 6° in the meniscus-deficient state failed to restore joint pressures and contact areas to the intact state, with significant changes in mean contact pressure (175%), mean peak contact pressure (135%), and contact area (–41%) (all P < .05 vs intact), while LMAT restored all outcome measures (all P > .05 compared with intact). After LMAT, every additional 1° of DFO correction contributed to a decrease in the mean contact pressure, peak pressure, and contact area of 5.6% (–0.0479 N/mm2), 5.9% (–0.154 N/mm2), and 1.4% (–6.99 mm2) for the lateral compartment and 7.3% (+0.034 N/mm2), 12.6% (+0.160 N/mm2), and 4.3% (+20.53 mm2) for the medial compartment, respectively. Conclusion: Isolated DFO was inadequate to restore load distribution in meniscus-deficient knees, while concomitant LMAT restored near normal forces and improved the lateral compartment biomechanical profile. Clinical Relevance Our findings support the concomitant use of LMAT and varus-producing DFO in the setting of lateral meniscal deficiency with valgus malalignment. This study provides tools for the orthopaedic surgeon to individualize the correction for each patient.

Biaxial tensile behavior of Ti-6Al-4V under proportional loading

The biaxial tensile behavior of isotropic Ti-6Al-4 V is characterized in this paper. A novel cruciform specimen was designed and optimized to achieve uniform stress and strain distribution within the gauge area. Biaxial tensile tests were conducted at three different loading ratios by the biaxial testing machine. The Digital Image Correlation (DIC) technique was applied to determine strain distribution, and a high-speed camera was employed to record the fracture process. An Inverse Analysis (IA) approach with a combined experimental and numerical method was proposed to determine the true stresses at the gauge section of the specimen during biaxial tensile tests. The results indicate that the initial yield locus can be described by the Cazacu criterion accurately, whereas the Mises criterion can predict better the strengthening behavior of Ti-6Al-4 V in the first quadrant in the principal stress space.

Experimental and theoretical investigation on compression-shear properties of high-strength engineered cementitious composites (HS-ECC)

High-strength engineered cementitious composites (HS-ECC) has broad application prospects due to its excellent mechanical performance and durability. Construction materials in structural members are susceptible to combined compression-shear stress. Therefore, the mechanical properties of HS-ECC under the combined stress are experimentally investigated by a servo-controlled biaxial testing machine. The effects of normal stress ratio on the compression-shear properties are systematically studied, and mortar specimens serve as control group. The experimental results show that the shear stress versus shear displacement curves of HS-ECC are able to be divided into four stages, namely linear ascending, non-linear ascending, rapid descending and stable stages. Compared with mortar specimens, the shear strength and residual shear strength of HS-ECC increase by 5–21% and decrease by 33–42% respectively. HS-ECC has a friction coefficient of 0.53, which is smaller than that of mortar specimens and concrete. When the normal stress ratio increases, the dilation angle of HS-ECC decreases at first and then remains basically unchanged. The damage evolution of HS-ECC is delayed when compared with that of the mortar specimen. Finally, a damage constitutive model is proposed to describe the compression-shear properties of HS-ECC. It is found that the predicted results agree well with the experimental results. This study is of great significance to understand the compression-shear properties of HS-ECC and promote its structural applications.

Investigation of Fatigue Crack Growth in TA2 Cruciform Specimen with an Inclined Crack, Considering Stress Ratio and Biaxial Load Ratio

The biaxial fatigue crack growth behavior of commercial pure titanium TA2 of cruciform specimens with different crack inclination angles (β = 90°, 60°, 45°) under various biaxial load ratios (λ = 0, 0.5, 1) and different stress ratios (R = 0, 0.1, 0.3) is studied by an IPBF-5000 biaxial testing machine. The test results prove that the maximum tangential stress criterion is suitable for predicting the initiation angle of uniaxial and biaxial mixed-mode I–II fatigue cracks. The fatigue crack growth rate of a cruciform specimen with mode I and mixed-mode I–II cracks decreases with the increase of biaxial load ratio and increases with the stress ratio. The Walker model and Kujawski model have better compression effects on fatigue crack growth data than the Paris model.

Experimental Study of Energy Evolution at a Discontinuity in Rock under Cyclic Loading and Unloading.

Energy is often dissipated and released in the process of rock deformation and failure. To study the energy evolution of rock discontinuities under cyclic loading and unloading, cement mortar was used as rock material and a CSS-1950 rock biaxial rheological testing machine was used to conduct graded cyclic loading and unloading tests on Barton’s standard profile line discontinuities with different joint roughness coefficients (JRCs). According to the deformation characteristics of the rock discontinuity sample, the change of internal energy is calculated and analyzed. The experimental results show that under the same cyclic stress, the samples harden with the increase in the number of cycles. With the increase of cyclic stress, the dissipated energy density of each stage gradually exceeds the elastic energy density and occupies a dominant position and increases rapidly as failure becomes imminent. In the process of increasing the shear stress step-by-step, the elastic energy ratio shows a downward trend, but the dissipated energy is contrary to it. The energy dissipation ratio can be used to characterize the internal damage of the sample under load. In the initial stage of fractional loading, the sample is in the extrusion compaction stage, and the energy dissipation ratio remains quasi-constant; then the fracture develops steadily, the damage inside the sample intensifies, and the energy dissipation ratio increases linearly (albeit at a low rate). When the energy storage limit is reached, the growth rate of energy dissipation ratio increases and changes when the stress level reaches a certain threshold. The increase of the roughness of rock discontinuity samples will improve their energy storage capacity to a certain extent.

Poster 216: The Effects of Lateral Opening Wedge Distal Femoral Osteotomy on Meniscus Allograft Transplantation: A Biomechanical Evaluation

Objectives:Lateral meniscus deficiency with valgus malalignment increases the risk and rate of lateral compartment osteoarthritis. Lateral meniscus allograft transplantation (LMAT) with concomitant varus-producing lateral opening wedge distal femoral osteotomy (LOWDFO) is an available option to treat this pathology. No biomechanical data currently exists evaluating the effect on joint forces with these combined procedures. The purpose of this study is to evaluate the effects of LMAT with concomitant varus-producing LOWDFO on lateral and medial compartment biomechanics. We hypothesize that LMAT restores lateral compartment biomechanics back to native intact forces, varus-producing LOWDFO improves lateral compartment forces following LMAT, and medial compartment forces change to a lesser degree in response to mechanical varus.Methods:Ten human cadaveric knees underwent varus-producing LOWDFO and were placed in an external fixator. Anatomic alignment was standardized for each knee and utilized as a proxy for mechanical alignment. Thin film Tekscan pressure sensors were placed sub-meniscal and specimens were loaded on a biaxial dynamic testing machine to 800N within a custom designed apparatus, with loading angles between 9° valgus and 6° varus of mechanical alignment. Testing conditions included the intact meniscus, lateral meniscus deficiency, and LMAT. Statistical analysis was performed by creating two-factor random-intercepts linear mixed-effects models to compare peak pressure and contact area among the three experimental meniscus conditions.Results:Isolated varus-producing LOWDFO to 6° varus in the setting of meniscus deficiency was unable to restore joint forces to the level of the intact meniscus in neutral alignment (Mean Contact Pressure: 175%, Peak Pressure 135%, Contact Area -41%, P>0.05). LMAT restored mean contact and peak pressures, with no significant differences compared to the intact meniscus (P<0.05). LMAT resulted in significantly lower contact areas from 9° valgus to 0° (P>0.05), but this was restored to intact state at 3° and 6° varus (P<0.05). Within the lateral compartment following LMAT, every additional 1° of DFO correction contributes to a decreased in mean contact pressure of 5.6% (-0.0479 N/mm2)(Figure 1), a decrease in peak pressure of 5.9% (-0.154 N/mm2)(Figure 2), and a decrease in contact area of 1.4% (6.99 mm2)(Figure 3), as compared to forces in neutral alignment. Within the medial compartment following LMAT, every additional 1° of DFO correction contributes to an increase in mean contact pressure of 7.3% (+0.034 N/mm2), an increase in peak pressure of 12.6% (+0.160 N/mm2), and an increase in contact area of 4.3% (20.53 mm2), as compared to forces in neutral alignment. However, baseline forces in the medial compartment are significantly lower at baseline compared to lateral compartment forces (P>0.05).Conclusions:This is the first biomechanical study evaluating the effects of concomitant LMAT and varus-producing LOWDFO. Isolated varus-producing LOWDFO is inadequate to restore forces in the meniscus deficient knee. LMAT restores near normal forces, and concomitant LOWDFO improves the lateral compartment biomechanical profile. Although to a smaller magnitude, force changes in the medial compartment are significant with varus-producing LOWDFO. Unloading to 0° following LMAT may be ideal. Overall, this study provides tools to for the surgeon to individualize alignment correction for each patient to optimize outcomes.Figure 1.Mean Contact PressureFigure 2.Peak Contact PressureFigure 3.Contact Area

Stress relaxation behavior of left ventricular myocardium in mice

BackgroundMyocardial tissues are known to exhibit viscoelastic behavior, i.e., the myocardial wall stress is gradually decaying when stretched at a constant level, referred to as stress relaxation behavior. The study of this behavior becomes important in structural heart diseases, where both passive and active relaxation behaviors of the myocardium may alter. As myocardial tissues display a complex, 3D micro‐architecture, the anisotropy of stress relaxation remains understudied. Our objective in this study was to investigate the anisotropy of (passive) stress relaxation behavior of the left ventricular (LV) myocardium in healthy small animals.MethodsWe used biaxial stress relaxation tests in wild‐type murine specimens (n=2). Full‐thickness myocardium LV free wall (LVFW) specimens were isolated from the mouse hearts (Fig. 1a), with the slab edges being aligned with the longitudinal (apex‐to‐outflow‐tract), circumferential, and radial directions of the LV. The specimens were mounted in a biaxial mechanical testing machine along the circumferential and longitudinal directions. The specimens were stretched in three different loading protocols with circumferential‐to‐longitudinal strain ratios of 30:30, 15:30, and 30:15%. The samples were loaded to the peak strain at a rate of 0.01 s‐1 and held at this stretch for 10 minutes to allow the relaxation. The time‐varying stress was recorded. We used an exponential decay fit to estimate the stress relaxation time constants in both directions.ResultsStress relaxation time constants showed noticeable differences between multiple loading ratios with equibiaxial loading (30:30) having the largest relaxation time constant followed by the circumferential stress in the 30:15 ratio (Fig. 1b). The larger strains led to larger stress relaxation constants (Fig. 1b‐c) indicating a strain‐dependent viscoelastic behavior. The quasi‐static equibiaxial loading of the same specimens resulted in a nearly isotropic behavior (not shown here), exhibiting insignificant contrast between the stresses in the circumferential and longitudinal directions. Interestingly, the contrast in the relaxation behavior between the circumferential and longitudinal directions were similarly insignificant (Fig. 1b). Non‐equibiaxial loadings (15:30 and 13:50) showed significantly faster relaxation for the direction with smaller strains (Fig. 1b).ConclusionsMyocardial tissue viscoelasticity is an important behavior contributing to both diastolic and systolic cardiac function, which remains understudied, especially in case of structural heart diseases associated with impaired relaxation in the LV. Our study suggests that stress relaxation behavior is prominent in the LV myocardium and may exhibit different relaxation behavior depending on strain magnitudes and strain ratios along different directions. The level of anisotropy in stress relaxation was found to be similar to the level of anisotropy in the tissue quasi‐static behavior. These results serve to motivate further studies to fully characterize the viscoelastic behavior of LV myocardium and its contribution to the LV relaxation and filling in murine models of LV diseases.

Experimental and numerical investigation of differential hardening of cold rolled steel sheet under non-proportional loading using biaxial tensile test

Strain path change is common phenomenon during industrial sheet metal forming processes. These strain paths can be proportional and non-proportional in nature. To enable strain path change in a single experiment is key challenge faced by many researchers. To predict deformation behavior accurately during such strain paths, it is required to represent initial yielding, the evolution of subsequent yield surface and hardening behavior precisely. This work deals with the mechanical characterization of Interstitial Free High Strength Steel (IFHS) during multi-axial proportional and non-proportional loading for the determination of yield surface evolution and strain hardening behavior. A set of tensile tests at various orientations with respect to the rolling direction and in-plane biaxial tests using cruciform specimens for various linear and bi-linear stress ratios were performed on as-received materials. It was found that at the onset of stress path change, the stress strain curve shows a change in the hardening rate for rolling and transverse directions of the biaxial specimen due to the change in active slip systems. To predict this behaviour various yield criterion like von Mises, Hill's 48 and Yld2000-2d were used. The experimental results show that the mechanical behavior of the subjected specimen deviates from isotropic behavior predicted by the von Mises and anisotropic behavior predicted by the Hill's 48 yield criterion. The initial yield loci measured by biaxial testing machine is in good agreement with what is predicted by Yld2000-2d yield criterion. However, it was observed that such phenomenological models were unable to capture the observed deformation behaviour. It is also shown that classical Crystal Plasticity Finite Element Method (CPFEM) can capture change in strain hardening rate during non-proportional deformation for few cases reasonably well while in few cases it could not predict.

Linear and volumetric wear of conventional and milled denture teeth.

The purpose of this study was to compare the linear and volumetric wear of conventional and milled double-cross-linked polymethyl methacrylate, nano-composite, and nano-ceramic infused resin posterior denture teeth. Double-cross-linked polymethyl methacrylate (PMMA) premolar teeth were scanned and used to mill denture teeth from a double-cross-linked PMMA resin disc and a nano-composite with nano-ceramic infused resin disc. The specimens (n=8: conventional double-cross-linked PMMA resin teeth-DCL, milled double-cross-linked PMMA resin teeth-DCL-CAM, conventional nano-composite infused resin teeth with four layers composed of composite and PMMA resin teeth-NC, and milled nano-composite and nano-ceramic infused resin teeth-NC-CAM) underwent chewing simulation in the biaxial fatigue testing machine at 1.53 Hz frequency, thermocycling between 5 and 55°C, and 49 N force against a Ø6mm steatite. After 250,000 cycles, the linear changes on the occlusal surfaces of the specimens were analyzed with pairwise comparison with Bonferroni post hoc test, and the volumetric changes of the specimens were analyzed with a one-way ANOVA with Bonferroni post hoc test (p < 0.05). The linear wear of the conventional and milled denture teeth was linearly correlated with the number of cycles between 50,000 and 250,000 cycles. After 250,000 cycles, NC had significantly more linear and volumetric wear (0.52 ± 0.10 mm and 4.29 ± 0.94 mm3 ) than DCL (0.18 ± 0.03 mm and 0.74 ± 0.14 mm3 ; p < 0.001) and NC-CAM (0.15 ± 0.03 mm and 0.35 ± 0.21 mm3 ; p < 0.001). DCL-CAM and NC-CAM had linearly and volumetrically equivalent wear to DCL (p > 0.05). NC-CAM had significantly less linear and volumetric wear (0.15 ± 0.03 mm and 0.35 ± 0.21 mm3 ) than DCL-CAM (0.24 ± 0.07 mm and 1.22 ± 0.61 mm3 ; p < 0.05). The conventional NC wore more than DCL, DCL-CAM, and NC-CAM. Both milled denture teeth wore an equivalent amount to conventional DCL. The wear between the conventional and milled DCL was equivalent. Denture teeth selection can prolong the retreading process and decrease the occurrences of prosthetic complications. Milled denture teeth are good alternatives to conventional denture teeth with regards to their wear resistance.

A systematic experimental study on the impact of multiaxiality on fatigue life of cast steels at high temperature

Rising demands on material performance at high temperature in components under complex loading such as gas turbine housings demand an increase in versatility and precision of component life modelling approaches. However, the database to train those models is commonly derived from uniaxial testing. The impact of multiaxial loading, both proportional and non-proportional, is usually addressed theoretically by the use of equivalent stress/strain formulations or reduction ratios derived from selective validation testing.In this study, the fatigue life of a cast steel is investigated systematically using a servo-hydraulic bi-axial test machine with induction heating. Each experiment is accompanied with finite element simulations before and after the test to parametrize the loading condition and derive hot-spot equivalent loading parameters. The impact of different load axis ratios is investigated systematically under displacement control as well as the effect of hold times.The results show that the modelled strain hot spots are coinciding with the observed crack initiation. A reoccurring sequence can be found in the impact of strain axis ratios on specimen life. Also, curve shift factors to compare the different combinations of axis ratio, temperature and hold time debit with uniaxial fatigue life data, have been identified.

Development of biaxial tensile testing for porous polymer membranes

Porous polymer membranes are typically polymeric materials that consist of many pores and complex network structures. As a result of these features, the membranes sometimes undergo anisotropic elastoplastic deformation. Hence, it is important to investigate the deformation behavior of these materials, including anisotropic deformation under multiaxial loading. In this study, we developed a new biaxial tensile testing machine for porous polymer membranes to evaluate their deformation behavior under biaxial tension and to understand the deformation mechanisms from their microstructure. First, uniaxial tensile tests were conducted to investigate changes in Young's modulus and yield strength for different tensile directions. These tests showed that the materials underwent anisotropic deformations. Next, we developed a novel biaxial tensile testing protocol for the membranes. It is usually difficult to grip the specimens and apply uniform deformations, as the membranes have low deformation rigidity and are very thin. Thus, a gripping component was developed to enable uniform tensile deformations to be applied. Stress–strain curves for each loading axis were obtained by changing the applied strain ratio. A yield surface based on the results was created to investigate the deformation behavior under biaxial tensile loading. We also investigated the deformation mechanisms of the porous microstructure via SEM observation.