Load-displacement Data Research Articles

Biomechanical evaluation of the impact of collared cementless total hip arthroplasty stems on implant subsidence: a cadaveric study in German Shepherd.

With the increasing use of cementless total hip arthroplasty (THA), stem subsidence has emerged as one of the primary complications. Although electron beam melting (EBM)-manufactured stems have been demonstrated to prevent subsidence, there has been limited investigation into the comparative biomechanical impact of collarless and collared EBM cementless stems on stem subsidence in veterinary medicine. This study aimed to compare the stem implant resistance and failure mechanical properties between collarless and collared EBM-manufactured stems. Seven pairs of femurs were harvested from canine cadavers. In each pair of femurs, the left femur was implanted with a collarless, and the right femur with a same-sized collared cementless stem. Specimen constructs were mounted to the loading frame of a testing machine and load was transferred to the femoral stem parallel to the longitudinal axis of the femur until the stem subsided 5 mm. Load and stem displacement data acquired during the tests were used to generate load-displacement curves and obtain stiffness, yield, and failure data for each specimen construct. Yield and failure energies were calculated as the areas under the load-displacement curves to the respective points. The effects of implant type and load during subsidence were analyzed using paired t-tests. The yield and failure loads for the collared stems were approximately 40% greater than for the collarless stems (156.39 ± 43.63 kgf vs. 112.01 ± 59.83 kgf, P<0.05). This study supported the advantages of collared EBM stems, including subsidence prevention and better initial stability for early osteointegration.

A novel device with pedicular anchorage provides better biomechanical properties than balloon kyphoplasty for the treatment of vertebral compression fractures

PurposeTo compare the biomechanical behavior of vertebrae with vertebral compression fractures (VCF) treated by a novel system with pedicular anchorage (dowelplasty) versus balloon kyphoplasty.MethodsFour cadaveric spines (T12-L5) were harvested, cleaned from soft tissues, and separated into vertebrae. Axial compressive loads were applied to each vertebra until a VCF was generated. Half of the vertebrae (n = 11) were instrumented using the “dowelplasty” system, consisting of a hollow titanium dowel anchored into the pedicle, through which a cannulated titanium nail is inserted and locked and through which cement is injected. The other half (n = 11) were instrumented using balloon kyphoplasty. Axial compressive loads were re-applied to each vertebra until fracture. Fracture load and fracture energy were calculated from load–displacement data for the pre- and post-treatment states.ResultsCompared to balloon kyphoplasty, dowelplasty granted greater net change in fracture load (373N; 95%CI,-331–1076N) and fracture energy (755Nmm; 95%CI,-563–2072Nmm). A sensitivity analysis was performed without L4 and L5 vertebrae from the dowelplasty group, since the length of the cannulated nails was too short for these vertebrae: compared to balloon kyphoplasty, dowelplasty granted an even greater net change in fracture load (680N; 95%CI,-96–1457N) and fracture energy (1274Nmm; 95%CI,-233–2781Nmm).ConclusionTreating VCFs with dowelplasty grants increased fracture load and fracture energy compared to the pre-treatment state. Furthermore, dowelplasty grants greater improvement in fracture load and fracture energy compared to balloon kyphoplasty, which suggests that dowelplasty may be a good alternative for the treatment of VCF.Level of evidencelevel IV.

Experimental and numerical study on the influence of cure process on the bridging traction mechanism of z-pins

This paper focuses on the bridging mechanism of individual z-pins embedded in carbon/epoxy laminates with curing effects into account. Based upon experiments, partial debonding exists in the vicinity of z-pins before pullout loading. Despite scatter, bi-linear relationship from load–displacement data is collected to characterize the bridging responses of z-pins. Complete pull-out is the dominant failure mode of z-pins after loading, due to inferior interfacial adhesion. A representative volume element (RVE) model of a single z-pin reinforced composite laminates is established, with resin-rich pockets and interfacial behavior into consideration. A qualitative analysis is presented to evaluate the influence of curing defects on the bridging ability of z-pins. The variations of cure-dependent properties are explicitly modeled. Cohesive elements are applied to the z-pin and interface regions in terms of bi-linear constitutive law. The predictions show reasonably well agreement with the experiments. Remarkably, the mismatched curing residual stresses are responsible for the generation of interfacial cracking around z-pins. The pre-existing cracking provides a reduction of physical interfacial contact, thus adversely controlling the effectiveness of z-pin reinforcement. Furthermore, the influence of cure process on the bridging behavior of z-pins is explored using a parametric method.

Origins of improved elongation to fracture in cyclic bending under tension of AA6022-T4 sheets as revealed using crystal plasticity modeling

Plastic instabilities can be suppressed by imposing cyclic bending during tension to increase elongation-to-fracture (ETF) of metallic sheets. This work is a combined experimental and modeling study into the origins of the improved ETF in cyclic bending during tension facilitated by a continuous-bending-under-tension (CBT) test. Load-displacement is measured during the CBT test under an optimized combination of band depth and pull speed process parameters for aluminum alloy (AA) 6022-T4. Monotonic and load reversal response of the alloy is also characterized under strain histories that resemble the history in CBT. Electron-backscattered diffraction and neutron diffraction are employed to characterize the initial microstructure and texture evolution of the alloy after CBT and simple tension (ST). Monotonic, load reversal, and texture data are used to adjust and verify the parameters of an elasto-plastic self-consistent crystal plasticity-based finite element model for simulating CBT. Additionally, a flow stress curve based on a bulge test is used to calibrate the model to capture the large strain hardening behavior of the alloy. The model is then used to simulate the CBT test while predicting the load-displacement and texture evolution data. The model successfully reproduced the succession of spikes and plateaus during CBT validating the prediction of the extrapolated hardening. After the validation, the development of stress and strain is probed through the sheet thickness to determine the underlying profiles as well as along the sheet to elucidate the location and onset of failure axially. The model reveals the development of more strain and dislocation density at the surface then at the center of the sheet and correctly predicts the strain localizations. Comparisons of texture evolution and mechanical fields developed in ST and CBT reveal very similar mechanical states in the sheet. These results in combination with experimental results suggest that the origins of improved ETF during CBT pertain primarily to the incremental deformation structural effects and secondary to the microstructural evolution effects.

Artificial intelligence based analysis of nanoindentation load–displacement data using a genetic algorithm

We developed an automated tool, Nanoindentation Neo package for the analysis of nanoindentation load–displacement curves using a Genetic Algorithm (GA) applied to the Oliver-Pharr method (Oliver et al.,1992). For some materials, such as polycrystalline isotropic graphites, Least Squares Fitting (LSF) of the unload curve can produce unrealistic fit parameters. These graphites exhibit sharply peaked unloading curves not easily fit using the LSF, which tends to overestimate the indenter tip geometry parameter. To tackle this problem, we extended our general materials characterization tool Neo for EXAFS analysis (Terry et al., 2021) to fit nanoindentation data. Nanoindentation Neo automatically processes and analyzes nanoindentation data with minimal user input while producing meaningful fit parameters. GA, a robust metaheuristic method, begins with a population of temporary solutions using model parameters called chromosomes; from these we evaluate a fitness value for each solution, and select the best solutions to mix with random solutions producing the next generation. A mutation operator then modifies existing solutions by random perturbations, and the optimal solution is selected. We tested the GA method using Silica and Al reference standards. We fit samples of graphite and a high entropy alloy (HEA) consisting of BCC and FCC phases.

A Gaussian process regression reduced order model for geometrically nonlinear structures

Reduced order models, such as Hollkamp and Gordon’s Implicit Condensation and Expansion (ICE) model, are a highly efficient alternative to full-order finite element models (FEM) of geometrically nonlinear structures. However, a reduced order model (ROM) is typically only valid for one FEM. It does not capture how each ROM coefficient changes due to variations in the FEM (e.g., design parameters or uncertainties), so if the FEM is updated then the ROM needs to be re-computed with a new set of static load–displacement data. This study presents a data-driven reduced order modeling approach that creates a single ROM that incorporates design variations in FEM. The proposed method applies Gaussian Process Regression (GPR) to the ICE approach, making each coefficient in an ICE ROM a regression model with respect to a collection of FEMs with varying material properties or geometric parameters. Once the GPR ROM has been identified, one can immediately produce an ICE ROM for a set of FEM parameters without a need to solve any static load–displacement cases on the full FEM. This dramatically enhances the computational efficiency and could be helpful when model uncertainty needs to be considered or when seeking to update a model to correlate with measurements. Additionally, the coefficients of a ROM can often change considerably if the scale on the load–displacement data changes, so it can be difficult to know whether the scaling that was chosen has really identified an accurate ROM. The proposed GPR ROM estimates the mean ROM coefficients for a range of load scaling as well as the uncertainty on each ROM coefficient with respect to the load level. This can be used to gauge the success of the ROM identification and to eliminate ROM coefficients that are unimportant and hence highly variable. The proposed GPR ROM approach is evaluated by applying it to flat and curved beam structures, revealing that the advantages outlined above can be realized with a relatively modest increase in cost relative to a traditional ICE ROM.

Influence of Multi Extrusion Die Process on Mechanical and Chemical Behavior of 2024-T3 Alloy

In this paper, a cold multi-pass extrusion process for a &lt;i&gt;15mm&lt;/i&gt; in diameter solid 2024-T3 aluminum alloy rod was carried out using three dies to obtain three different diameters of &lt;i&gt;14mm, 13mm&lt;/i&gt;, and &lt;i&gt;12mm&lt;/i&gt;. The microstructure, hardness, and corrosion behavior were investigated before and after the extrusion process. Load-Displacement data were recorded during each extrusion process. The electrochemical corrosion test was made in a &lt;i&gt;3.5 wt.&lt;/i&gt;% NaCl solution using potentiostat instrument under static potentials test. Corrosion current was recorded to determine the corrosion rate for specimens. The results showed that the extrusion load increased with the number of extrusion passes, which is also seen in hardness test results. In addition, the corrosion rate decreased with the increase in the number of extrusion passes. This is due to severe plastic deformation, which generates a fine grain structure of (AlCu) and (AlCuMg) components.

Mode II fracture characterisation of a honeycomb/carbon-epoxy sandwich panel using the asymmetric end-notched flexure test

The objective of this work is to determine the fracture energy of a honeycomb/carbon-epoxy sandwich panel under mode II loading using the Asymmetric End-Notched Flexure (AENF) test. Experimental tests and numerical analyses aiming to validate all the procedures were performed. An equivalent crack length data reduction scheme was developed in order to simplify the experimental determination of the Resistance-curves ( R-curves) using exclusively the load-displacement ( P- δ) data. This strategy makes unnecessary the crack length monitoring during its propagation, which is hard to perform in mode II fracture tests. A mixed-mode I+II trapezoidal cohesive zone model was used for validating the proposed data reduction method. It was concluded that this methodology constitutes a suitable procedure for mode II fracture characterisation of debonding failure in composite sandwich panels.

Investigation of dynamic mechanical properties and constitutive model of (010) plane of gallium oxide crystals under shock loading

In this study, ultraprecision processing performance of new-generation optoelectronic gallium oxide crystals is investigated. Based on material mechanics, Hopkinson rod test is carried out on (010) crystal plane of gallium oxide crystal. The destruction process of gallium oxide crystals was observed by high-speed photography and three-dimensional topography. Through this experiment, the dynamic mechanical properties of the (010) crystal plane of the gallium oxide crystal were tested, and the real stress-strain curves at different rates were obtained.The formation mechanism of fracture after crystal crushing was analyzed. It was found that the compressive strength and yield strength of gallium oxide crystals showed a significant plastic increase with the increase of the impact speed, while the plastic failure strain decreased with the increase of the impact speed. Furthermore, dynamic mechanical properties of (010) crystal plane of gallium oxide crystal are tested, and actual stress-strain curves are obtained. The fracture process of gallium oxide crystals is observed via high-speed photography. Formation mechanism of fractures is analyzed using three-dimensional topography. AlongsideCombined with the quasistatic indentation test, a set of Holmquist–Johnson–Cook constitutive models suitable for gallium oxide crystals is established. Based on obtained parameters, finite element software ABAQUS is used to numerically simulate nanoindentation test of gallium oxide crystals. By comparing numerically and experimentally obtained load-displacement curve data, validity of parameters of constitutive model is verified. It provides a certain guiding significance for the subsequent ultra-precision machining of gallium oxide crystals.

Prediction of Ultimate Antifloating Force of Bored Piles in Urban Road Crossing Overpass

As an effective antifloating measurement in underpass engineering, uplift piles have been widely employed in the antifloating design of underground structures, such as basements, underground roads, and underground shopping malls. For the purpose of studying the antifloating behavior of bored piles and predicting the uplift bearing capacity in underpass engineering, the on-site pull-out tests of bored piles are carried out in laboratory. Besides, the MMF growth curve model, the ordinary hyperbolic model, and the exponential model are employed to fit and predict the ultimate bearing capacity of the measured uplift load and uplift displacement data of three test piles, respectively. The research results indicate that three test piles meet the stability requirements of antibuoyant bearing capacity, and the pull-up load-displacement curves of test piles are gentle and steep. Meanwhile, the fitting accuracy of the pull-displacement curve is high; specifically, the correlation coefficient is above 0.98619, and the average value is 0.99134, thereby verifying that the fitting effect of MMF growth curve model is better than those of the hyperbolic model and the exponential model. Therefore, the MMF growth curve model proposed in this paper not only describes the fitting of the uplift load-uplift displacement curve of uplift piles accurately but also predicts the ultimate bearing capacity of test piles. The research results provide an important reference for the antifloating behavior of bored piles in underpass engineering.

On the Viscoelastic Drift Behavior During Nanoindentation

Nanoindentation measurements frequently involve a hold period at the peak load to allow the material to reach a stabilized state. A dwell time is also commonly employed at a sufficiently low load after unloading, to quantify the thermal drift for correction of the raw load-displacement data. This communication presents numerical case studies of indentation loading on a viscoelastic thin film using the finite element method. We illustrate that a simple viscoelastic material can actually induce prominent drift even under a low indentation load. The drift is caused by the material itself, unrelated to the thermal drift of the instrument. The direction and magnitude of the viscoelastic drift are controlled by the prior loading/unloading history as well as the load-displacement response of the fully relaxed elastic state.

Analysis of the tension chord in the flexural response of concrete elements: Methodology and application to weft-knitted textile reinforcement

The use of high-strength fibrous materials offers great potential to serve as the main reinforcement in the flexural response of lightweight concrete structures. Specifically, weft-knitted textile reinforcement allows creating complex geometries (i.e. doubly curved or folded) and introducing straight inlays as well as spatial features such as ribs within the fabric to enhance the bond conditions between the reinforcement and the concrete. While the evaluation of uniaxial tension tests to characterise the mechanical behaviour is usually straightforward, the vast majority of bending tests of textile reinforced concrete elements in the literature are limited to load–displacement data, which does not give direct information on the mechanical behaviour and makes it difficult to compare specimens with different geometries or reinforcement contents. This study presents a methodology based on digital image correlation measurements to directly assess the response in the tension chord of reinforced concrete beams in four-point bending. This methodology was applied and validated in an experimental campaign consisting of 16 bending tests with weft-knitted textile reinforcement. Various fibre materials, coating types and specimen geometries were tested, and the results were compared to corresponding uniaxial tension tests with the same type of reinforcement, generally showing a good agreement in the load-deformation behaviour and the crack kinematics. However, the textile reinforcement could not be utilised to the tensile strength obtained in uniaxial tension since all bending beams failed prematurely either in a combined bending-shear type failure (for most of the cement paste-coated textiles) or due to the delamination of the textile within a shear crack (for all epoxy-coated textiles). The Tension Chord Model with an assumed constant bond-slip relationship and an equivalent reinforcement ratio in bending yielded a good prediction of the stress–strain relationship, the tension stiffening effect, the crack widths and spacing.

Effects of Fe atoms on hardening of a nickel matrix: Nanoindentation experiments and atom-scale numerical modeling

Significant hardening effect due to Fe concentrations in Ni-based alloys with face-centered-cubic structure has been studied by using a combined experimental and atomistic-based computational approach via nanoindentation tests. The obtained experimental load–displacement data for the [001] crystal orientation reached a qualitative good agreement with molecular dynamics simulations results, leading to strong evidence that the main strengthening factors are associated to sluggish dislocation diffusion, reduced defect sizes and the nucleation of tetrahedral stacking faults. Here, interstitial type prismatic dislocation loops mainly formed by ⅙〈112〉 Shockley dislocations are nucleated during the loading process, where their interaction leads to the formation of pyramidal shaped stacking fault which are mainly created by ⅓〈100〉 Hirth dislocations lines. Observing both types of defects coexisting in the same plastic deformation zone by both approaches. Reported mechanical data, measured experimentally and interpreted numerically, are also in accordance with microstructural SEM and TEM investigations.

Identification of parameter to assess cracking resistance of asphalt mixtures subjected to aging and moisture conditioning

This study comprehensively evaluated different parameters based on tensile strength testing to assess the cracking resistance of asphalt mixtures subjected to aging and moisture conditioning. For this purpose, two sources of aggregates were selected to produce hot and warm mix asphalt mixtures. Asphalt mixtures were subjected to short term and long term aging, three levels of moisture conditioning (freeze thaw cycles), and tested at two temperatures (15 °C and 25 °C). The load-displacement data was used to determine the fracture work density, fracture energy, toughness index, cracking resistance index, cracking tolerance index, and rate dependent cracking index. It was noticed that moisture conditioning increased the variability of the different parameters. The cracking tolerance index and rate dependent cracking index parameter had a much higher coefficient of variation (CoV) with a maximum value close to 50%. Indirect tensile strength, fracture energy, and fracture work density appropriately captured the effect of moisture on cracking resistance of mixtures. The cracking resistance index, cracking tolerance index, and rate dependent cracking index increased with an increase in the moisture conditioning level. The Statistical analysis showed that tensile strength, fracture work density, and fracture energy were significantly influenced by different aging and moisture conditions evaluated. Fracture energy showed better association with fatigue life of asphalt mixtures subjected to three freeze-thaw cycles compared to tensile strength. Further, the fatigue life prediction models showed that both indirect tensile strength and fracture energy significantly influence the fatigue life of asphalt mixtures subjected to aging and moisture conditioning.

Irradiation hardening of advanced tungsten grades: An experimental and inverse finite element method study

The effect of neutron irradiation on mechanical properties of various advanced W grades (pure, doped by K, alloyed by Re) was assessed by means of mechanical testing using miniaturized tensile and sub-miniaturized three-point bending (3PB) specimens. Different irradiation conditions in terms of temperature (400, 600, 800 and 1100 °C) and irradiation dose (0.2–0.25 dpa, 1.0–1.1 dpa) were considered. In order to extract the yield stress from the flexural load-displacement data, the empirical correlation between the flexural stress at a specific reference point on the flexural stress-strain curve and uniaxial tensile yield stress was established. The empirical ratio identified can be applied for the 3PB testing in a wide range of temperatures and plastic properties of un-irradiated and irradiated W alloys. The accuracy of the yield stress determination deduced using the empirical correlation from the 3PB tests was compared with the inverse FEM modelling procedure applied to the 3PB tests carried along with reference data extracted from the dedicated tensile tests. The information on the tensile yield stress and work hardening rate of all studied materials at different irradiation conditions was summarized and discussed in the view of the irradiation hardening.

A complex-variable finite element method-based inverse methodology to extract constitutive parameters using experimental data

This paper presents the use of full-field kinematic measurements obtained using the digital image correlation (DIC) procedure and load–displacement data to determine constitutive material properties by solving an inverse finite element optimization problem. A key ingredient in the proposed approach is computing accurate sensitivities with respect to the unknown parameters. These sensitivities were used to solve the optimization problem using an accurate, efficient, gradient-based method, and were computed using the complex-variable finite element method, ZFEM. The use of ZFEM’s gradients to inversely determine material properties is demonstrated with two examples. First, the elastic–plastic material properties of DP-590 steel are obtained using a tensile test specimen. Second, the cohesive material parameters of an adhesive are determined using a double cantilever beam test. A significant outcome of this paper is that the use of a weighted residual formulation of the interfacial strain fields and the load–displacement data within the optimization procedure provides better estimates of the constitutive properties than using only the load–displacement data. This technique minimizes the relative error in both the strain fields and the load–displacement curve, which is important to obtain accurate interfacial properties.

Determination and Verification of GISSMO Fracture Properties of Bolts Used in Radioactive Waste Transport Containers.

Transport containers for radioactive materials should withstand drop tests according to the regulations. In order to prevent a loss or dispersal of the internal radioactive materials in the drop tests, a tightening of the lid of the transport container should be maintained. The opening of the lid, due to the drop impact, might cause the dispersion of internal contents or a loss of shielding performance. Thus, it is crucial to predict damage to the fastening bolt and its fracture. In this study, the damage parameters of the fastening bolt were acquired, and its fracture was predicted using the generalized incremental stress state-dependent damage model (GISSMO), a phenomenological damage model. Since the dedicated transport container is large and heavy, various jigs that can simulate the fall of the container were designed, and the accuracy of fracture prediction was verified. Digital image correlation (DIC) was introduced for the accurate measurement of the displacement, and load–displacement data for tensile, shear, and combined loads were successfully acquired. Finally, the load–displacement curve of the finite element analysis (FEA) with GISSMO until the point of the bolt fracture was compared with the curve obtained from the experiment, where a good agreement was observed.

An efficient semi-analytical method to extract the mode II bridging-traction law in ENF tests directly from the experimental load displacement data

Large scale fiber bridging ahead of the crack tip of ENF specimen is one of the most common toughening mechnisms, leading to a significant resistance phenomenon on the fracture toughness. In order to account for the toughening effect of the fiber bridging to accurately model the delamination of composite laminates, a physically semi-analytical method is presented to determine the mode II bridging law with the assumption of linear form directly from the experimental load displacement curve. The method includes the deflection analysis of the ENF specimen based on the beam theory considering the closing force introduced by fiber bridging and the inverse method iteratively determining the bridging law parameters. To validate the proposed method, the identified bridging tractions by the current method are integrated in the traditional cohesive law to simulate the whole delamination propagation process of undirectional laminates with different materials and multidirectional laminates. Good agreements between the numerical results and experimental ones indicate the accuracy and the applicability of the current method. The major advantage of the proposed method is that it reduces the instructmentation needed in the delamination test and it can be adopted as an efficient method to investigate the delamination behaviour of specimens.

A new method for interpreting Vickers indentation measurements

A new method for interpreting Vickers microindentation data is proposed, based on continuum mechanics and, more precisely, the Gradient Elasticity framework. The main feature is the elastic properties’ calculation from the initial (elastic) region of the load vs. depth indentation data, which makes the calculation independent of the maximum indentation depth. This approach deviates significantly from the semi-empirical method of Oliver and Pharr, which calculates the material properties (such as elastic modulus and hardness) from the elastic unloading region, with the calculated values of the elastic modulus and hardness being strongly dependent on the indentation depth and, therefore, giving rise to the so-called indentation size effect (ISE). The proposed framework considers the Vickers indentation as a compression test with a complex geometry, as the pyramidal indenter tip applies load to directions perpendicular to its four faces. An elastic displacement field is initially assumed following Boussinesq’s solution before an indent is made, while afterwards the displacement of the material in contact with the tip is assumed to follow the Vickers tip’s geometry. The respective von Mises equivalent strain calculated through a continuum mechanics approach can qualitatively capture thin film delamination micrographs and shear band formation, showing the potential of the present formulation to model such micro-deformation problems. The traction vector calculated on each of the four sides of the Vickers tip, leads to the generation of load-displacement data, which compare well with experimental indentation data, with the elastic properties (i.e. elastic modulus) thus calculated being in accordance with the corresponding literature values.

J-resistance curve testing of a pressure vessel steel and a clad pipe girth weld using clamped SE(T) specimens and the normalization method

This work addresses an exploratory application of the normalization method to determine crack growth resistance curves for a typical pressure vessel steel and a clad pipe girth weld using clamped SE(T) specimens. A primary objective is to verify the effectiveness of the methodology in providing accurate descriptions of the ductile properties for the tested materials using clamped SE(T) specimens. Fracture toughness testing conducted on an A285 Gr C pressure vessel steel and a dissimilar Nickel–Chromium girth weld provides the load–displacement data from which J-resistance curves are evaluated on the basis of the normalization procedure. For the tested pressure vessel steel and clad pipe girth weld, the normalization method provides experimental measurements of ductile crack extension in terms of J−Δa curves which are in good agreement with experimentally measured crack growth responses derived from the UC procedure.