Peak Compressive Stress Research Articles

Subject-specific evaluation of patellofemoral joint biomechanics during functional activity

Patellofemoral joint pain is a common problem experienced by active adults. However, relatively little is known about patellofemoral joint load and its distribution across the medial and lateral facets of the patella. In this study, biomechanical experiments and computational modeling were used to study patellofemoral contact mechanics in four healthy adults during stair ambulation. Subject-specific anatomical and gait data were recorded using magnetic resonance imaging, dynamic X-ray fluoroscopy, video motion capture, and multiple force platforms. From these data, in vivo tibiofemoral joint kinematics and knee muscle forces were computed and then applied to a deformable finite-element model of the patellofemoral joint. The contact force acting on the lateral facet of the patella was 4–6 times higher than that acting on the medial facet. The peak average patellofemoral contact stresses were 8.2±1.0MPa and 5.9±1.3MPa for the lateral and medial patellar facets, respectively. Peak normal compressive stress and peak octahedral shear stress occurred near toe-off of the contralateral leg and were higher on the lateral facet than the medial facet; furthermore, the peak compressive stress (11.5±3.0MPa) was higher than the peak octahedral shear stress (5.2±0.9MPa). The dominant stress pattern on the lateral patellar facet corresponded well to the location of maximum cartilage thickness. Higher loading of the lateral facet is also consistent with the clinical observation that the lateral compartment of the patellofemoral joint is more prone to osteoarthritis than the medial compartment. Predicted cartilage contact stress maps near contralateral toe-off showed three distinctly different patterns: peak stresses located on the lateral patellar facet; peak stresses located centrally between the medial and lateral patellar facets; and peak stresses located superiorly on both the medial and lateral patellar facets.

Simulation and Measurement of Through–Wall Residual Stresses in a Structural Weld Overlaid Pressurizer Nozzle

Full structural weld overlays (FSWOLs) have been used extensively as a repair/mitigation technique for primary water stress corrosion cracking in pressurizer nozzle dissimilar metal (DM) welds. To support an approved FSWOL design and safety submission for British Energy pressurized water reactor (PWR) nozzles, an in-depth evaluation was performed to assess the effects of a FSWOL on the through wall residual stress distribution in safety/relief pressurizer nozzles. Two safety/relief pressurizer nozzle mockups were fabricated based on British Energy’s PWR nozzle design. One mockup included the nozzle to safe-end DM weld and the safe-end to stainless steel weld, while the second mockup included the DM weld, the stainless steel weld, and a Westinghouse designed structural weld overlay. The mockups were fabricated utilizing materials and techniques that represented the plant specific nozzles as closely as possible and detailed welding parameters were recorded during fabrication. All welds were subsequently nondestructively evaluated (NDE). A thorough review of the detailed fabrication records and the NDE results was performed and several circumferential positions were selected on each mockup for subsequent residual stress measurement. The through wall residual stress profiles were experimentally measured through the DM weld centerline at the selected circumferential positions using both the deep-hole drilling (DHD) and incremental deep-hole drilling (iDHD) measurement techniques. In addition to experimental residual stress measurements, the through-wall residual stress profiles were simulated using a 2D axisymmetric ansys™ finite element (FE) model. The model utilized the application of temperature constraints on the weld elements to simulate the thermal welding cycle which greatly simplified the simulation as compared with detailed heat source modeling methods. Kinematic strain hardening was used for material modeling of the weld and base metals. A range of residual weld stress profiles was calculated by varying the time at which the temperature constraints were applied to the model. The simulation results were compared with the measurement results. It was found that the effects of the FSWOL were principally threefold. Specifically, the FSWOL causes a much deeper compressive stress field, i.e., the overlay shifts tension out toward the outside diameter (OD) surface. Furthermore, the FSWOL reduces tension in the underlying dissimilar metal weld, and finally, the FSWOL causes higher peak compressive and tensile residual stresses, both of which move deeper into the nozzle wall after the overlay is applied. Relatively good agreement was observed between the FE results and the measurements results.

Influence of shock loading kinetics on the spall response of copper

A suite of plate-impact experiments was designed and conducted to examine the influence of loading kinetics on the spall response of high purity copper samples. The peak compressive stresses (1.5 GPa) and the density of grain boundaries dynamically loaded were held constant for all experiments. The kinetics of the tensile pulses were designed using a hydrodynamic, shock-wave propagation code and experimentally achieved by controlling the geometry of copper impactors and targets. Examination of damage fields shows that the total fraction of damage (voids) increases as the tensile rates decrease. In addition, an accompanying larger plastic dissipation, in the form of grain misorientation measured by means of electron backscatter diffraction, is present in the samples deformed at lower tensile rates. These results suggest a time dependent behaviour of the processes the plastic processes for void growth.

Effect of Stent Radial Force on Stress Pattern After Deployment: A Finite Element Study.

The present article presents a method for assessing the radial stiffness of nitinol stents. An idealized stent model was created, and its radial stiffness was calculated by means of finite element modeling. The calculations were validated against experimental measurements. The variation of radial stiffness with geometrical dimensions was calculated, and the effect of increasing radial stiffness on endovascular deployment was analyzed. Peak tensile and compressive stresses as well as stent penetration were calculated in the case of an idealized pulmonary artery model having realistic dimensions as well as stiffness. The results of stress calculations were compared with a second set of simulations, where an idealized behavior of the stent (uniform expansion to a theoretical contact diameter) was modeled. The results show how in reality nitinol stents behave in a non-ideal way, having a non-uniform expansion and exerting non-uniform pressure on the contact areas with the artery. Such non-ideality decreases though with the increase in radial stiffness. The radial force alone may be insufficient in describing the stent-artery interaction, and numerical modeling proves to be necessary for capturing such complexity.

Analysis of residual stress and work-hardened profiles on Inconel 718 when face turning with large-nose radius tools

Surface integrity (SI) and, particularly, the residual stress profile, has a great influence on the fatigue life of machined aeronautical critical parts. Among the different cutting parameters that affect the final SI, tool geometry is one of the most important factors. In particular, tool nose radius determines the surface roughness, as well as the thermoplastic deformation of the workpiece. Indeed, the use of large tool nose radius in the industry enables (1) increasing the feed rate while keeping the roughness values below specifications and (2) reducing the influence of the tool wear in the surface roughness. Therefore, in this study, the influence of tool nose radius in the induced residual stress profile and work-hardened layer when face turning Inconel 718 is analysed for a cutting speed range between (30–70 m/min) and a feed rate range of (0.15–0.25 mm/rev). For this purpose, residual stress profiles and work-hardened layer were measured by x-ray diffraction method after machining with a 4 mm nose radius. Then, results have been compared against different tool nose radius studies carried out by other authors for the specified working conditions. Results revealed that residual stress profiles varied when machining with different nose radius for the studied range. In particular, the increase of the nose radius brought to a higher difference between surface tensile stress and subsurface compressive peak stress, which is attributed to an increase of the thermal effect. Moreover, thicker work-hardened layer (around 100 μm) was observed when machining with large-nose radius for the studied working conditions.

Empirical Modeling of Residual Stress Profile in Machining Nickel-based Superalloys Using the Sinusoidal Decay Function

After machining nickel-based superalloys, tensile surface residual stresses can cause end-product issues such as fatigue failure. Modeling the residual stress profile is currently tedious and inaccurate. This study introduces a new method of understanding the residual stress profile in terms of quantifiable key measures: peak tensile stress at the surface, magnitude and depth of peak compressive stress, and depth at which residual stress becomes near-zero. Experiments in turning IN-100 and milling GTD-111 have been conducted and subsequent X-ray Diffraction measurements have been utilized to obtain residual stress profiles. Using a sinusoidal decay function fitted to measured residual stress profiles, these four key profile measures are extracted and then the effects of process parameters such as cutting speed, feed, cutting edge radius, and tool coating on these measures are investigated.

Compressive strength and energy absorption of sandwich panels with aluminum foam-filled corrugated cores

Abstract All-metallic corrugate core sandwich panels as primary loading structures may rapidly soften under compressive loading due mainly to core member buckling once the peak compressive stress is reached, resulting in reduced load-carrying capability. Inserting close-celled aluminum foam into the corrugate core has been envisioned as a feasible way to enhance the load capacity. The enhancement due to foam filling were firstly explored experimentally under quasi-static out-of-plane compression and the underlying mechanisms subsequently numerically studied using finite element simulations. The foam filled corrugated panel was found to have strength and energy absorption much greater than the sum of those of an empty corrugated sandwich panel and the aluminum foam alone. It was demonstrated that the core members in the foam-filled panel were considerably stabilized by the filling foam against lateral deflection. In particular, the elastoplastic buckling wavelength of the core members was significantly reduced and the transition from axial deformation to bending of the core member was much delayed, both of which contributing to the enhanced strength and energy adsorption capability of the foam filled panel.

Multiobjective Optimization of Experimental and Simulated Residual Stresses in Turning of Nickel-Alloy IN100

In this study, physics-based simulations are utilized to predict the forces and residual stresses induced during machining, and the results were validated using the experimental measurements. Physics-based simulations also involve uncertainty in the predicted values that can be represented as expected value and variance of the predictions. These predictions are inputted to a multiobjective optimization methodology to select the optimal machining parameters where competing or conflicting objectives constitute hurdles in the decision-making of the manufacturing plans. The objectives are chosen as related to residual stress measurements and predictions. Multiobjective particle swarm optimization (PSO) procedure is employed in optimizing process parameters. Objectives are solved for minimizing tensile residual stresses on the surface, maximizing peak compressive residual stresses, and minimizing the variance of these variables in order to increase certainty in the predictions. The optimum machining parameters corresponding to this multiobjective optimization are represented in both objective function and decision variable spaces.

Effect of grain size and arrangement on dynamic damage evolution of ductile metal

Plate-impact experiments have been carried out to examine the effect of grain size and grain arrangement on the damage evolution of ultrapure aluminum. Two groups of samples, “cross-cut“ and “longitudinal-cut,“ are obtained from the rolled aluminum rod along different directions. The peak compressive stress is approximately 1.25 GPa−1.61 GPa, which can cause incipient spall damage that is correlated to the material microstructure. The metallographic analyses of all recovered samples show that nearly all damage nucleates at the grain boundaries, especially those with larger curvature. Moreover, under lower shock stress, the spall strength of the “longitudinal-cut“ sample is smaller than that of the “cross-cut“ sample, because the different grain sizes and arrangement of the two samples cause different nucleation, growth, and coalescence processes. In this study, the difference in the damage distribution between “longitudinal-cut“ and “cross-cut“ samples and the causes for this difference under lower shock-loading conditions are also analyzed by both qualitative and semi-quantitative methods. It is very important for these conclusions to establish a reasonable and perfect equation of damage evolution for ductile metals.

The effect of meniscal tears and resultant partial meniscectomies on the knee contact stresses: a finite element analysis

Knee osteoarthritis (OA) is believed to result from high levels of contact stresses on the articular cartilage and meniscus after meniscal damage. This study investigated the effect of meniscal tears and partial meniscectomies on the peak compressive and shear stresses in the human knee joint. An elaborate three-dimensional finite element model of knee joint including bones, articular cartilages, menisci and main ligaments was developed from computed tomography and magnetic resonance imaging images. This model was used to model four types of meniscal tears and their resultant partial meniscectomies and analysed under an axial 1150 N load at 0° flexion. Three different conditions were compared: a healthy knee joint, a knee joint with medial meniscal tears and a knee joint following partial meniscectomies. The numerical results showed that each meniscal tear and its resultant partial meniscectomy led to an increase in the peak compressive and shear stresses on the articular cartilages and meniscus in the medial knee compartment, especially for partial meniscectomy. Among the four types of meniscal tears, the oblique tear resulted in the highest values of the peak compressive and shear stresses. For the four partial meniscectomies, longitudinal meniscectomy led to the largest increase in these two stresses. The lateral compartment was minimally affected by all the simulations. The results of this study demonstrate meniscal tear and its resultant partial meniscectomy has a positive impact on the maintenance of high levels of contact stresses, which may improve the progression of knee OA, especially for partial meniscectomy. Surgeons should adopt a prudent strategy to preserve the greatest amount of meniscus possible.

On Plastic Deformation and Fracture in Si Films during Electrochemical Lithiation/Delithiation Cycling

An in situ study of deformation, fracture, and fatigue behavior of silicon as a lithium-ion battery electrode material is presented. Thin films (100–200 nm) of silicon are cycled in a half-cell configuration with lithium metal foil as counter/reference electrode, with 1M lithium hexafluorophosphate in ethylene carbonate, diethylene carbonate, dimethyl carbonate solution (1:1:1, wt%) as electrolyte. Stress evolution in the Si thin-film electrodes during electrochemical lithiation and delithiation is measured by monitoring the substrate curvature using the multi-beam optical sensing method. The stress measurements have been corrected for contributions from residual stress arising from sputter-deposition. An indirect method for estimating the potential errors due to formation of the solid-electrolyte-interphase layer and surface charge on the stress measurements was presented. The films undergo extensive inelastic deformation during lithiation and delithiation. The peak compressive stress during lithiation was 1.48 GPa. The stress data along with the electron microscopy observations are used to estimate an upper bound fracture resistance of lithiated Si, which is approximately 9–11 J/m2. Fracture initiation and crack density evolution as a function of cycle number is also reported.

Stress Evolution in Composite Silicon Electrodes during Lithiation/Delithiation

We report real-time average stress measurements on composite silicon electrodes made with two different binders – viz. Carboxymethyl cellulose (CMC) and Polyvinylidene fluoride (PVDF) – during electrochemical lithiation and delithiation. During galvanostatic lithiation at very slow rates, the stress in a CMC-based electrode becomes compressive and increases to 70 MPa, where it reaches a plateau and increases slowly thereafter with capacity. The PVDF-based electrode exhibits similar behavior, although with lower peak compressive stress of about 12 MPa. These initial experiments indicate that the stress evolution in a Si composite electrode depends strongly on the mechanical properties of the binder. Stress data obtained from a series of lithiation/delithiation cycles suggests plasticity induced irreversible shape changes in contacting Si particles, and as a result, the stress response of the system during any given lithiation/delithiation cycle depends on the cycling history of the electrode. While these results constitute the first in situ stress measurements on composite Si electrodes during electrochemical cycling, the diagnostic technique described herein can be used to assess the mechanical response of a composite electrode made with other active material/binder combinations.

Evaluation of stress distribution and failure mechanism in lanthanum–titanium–aluminum oxides thermal barrier coatings

LaTi2Al9O19 (LTA) is one of the most promising materials for new thermal barrier coatings (TBCs) to fulfill the demand of advanced gas turbines owing to its high temperature stability and low thermal conductivity. In the present study, a finite element (FE) based numerical study has been carried out to investigate the stress distribution in LTA single layered coating system in comparison with traditional yttria stabilized zirconia (YSZ) TBC. Stresses in YSZ/LTA double ceramic layer TBC system are also determined and presented for comparative analysis. The thermal cycling effect is simulated by sequent increment in TGO thickness in a series of FE simulations. In-plane stresses (σxx), out-of-plane stresses (σyy) and shear stresses (σxy) are determined for all systems, and peak stress values are presented for quantitative comparison. Elastic strain energy stored in TGO of all systems is calculated from FE results for TBC structural integrity assessment. It has been found that maximum in-plane and shear stresses are lower in the double ceramic layer coating system than in the single layer ceramic coating system. However, peak axial tensile and compressive stresses in the double ceramic layer coating are very close or higher than those in the single layer topcoat. Calculation of elastic store energy shows that double ceramic layer TBC system may exhibit better stability as compared to single layer systems. Results are presented to explain the failure mechanism in LTA coatings.

Evaluation of high-resolution peripheral quantitative computed tomography, finite element analysis and biomechanical testing in a pre-clinical model of osteoporosis: A study with odanacatib treatment in the ovariectomized adult rhesus monkey

This study aimed to validate finite element analysis (FEA) estimation of strength, identify high-resolution peripheral quantitative computed tomography (HR-pQCT) measures correlating with strength, and evaluate the precision of HR-pQCT measurements to longitudinally monitor effects of osteoporosis treatment in ovariectomized (OVX) non-human primates (NHPs). HR-pQCT images were acquired in three groups of NHPs: Intact (n=10), OVX-odanacatib treated (OVX-ODN 30mg/kg, n=10) and OVX-vehicle treated (OVX-Veh, n=10) at the ultradistal (UD) and distal 1/3 radii and tibia at 12, 16 and 20months. FEA estimates of bone strength using the Pistoia criterion were validated by ex-vivo mechanical compression (r2=0.95) of the UD radius. Single linear regressions of FEA-determined ultimate stress showed high correlation with HR-pQCT derived parameters: integral vBMD (r2=0.86), bone volume fraction (r2=0.84) and cortical thickness (r2=0.79). Precision of HR-pQCT measurements, obtained from an excised radius and tibia, showed low variation (CV=0.005%–5.6%) and helped identify possible sources of error. Comparison of OVX-Veh and Intact groups showed decreases in bone parameters demonstrating trends consistent with bone loss. Comparison of OVX-ODN and OVX-Veh groups showed a treatment effect with increases in bone parameters: integral vBMD (477±27 vs. 364±22mgHA/cm3) and cortical thickness (Ct.Th) (0.90±0.07 vs. 0.64±0.04mm) at the UD radius, Ct.Th (2.15±0.28 vs. 1.56±0.08mm) at the distal 1/3 radius. Axial compression peak stress calculated and obtained experimentally showed the OVX-ODN group was 33% stronger than the OVX-Veh group. We conclude that HR-pQCT and FEA serve as robust techniques to longitudinally monitor bone parameters and strength in NHP's.

Experimental testing and analytical modeling of CFRP-confined large circular RC columns subjected to cyclic axial compression

A physically informed analytical model which describes the cyclic axial stress–strain behavior of reinforced concrete (RC) columns confined with fiber-reinforced polymer (FRP) composite wraps is necessary for the non-linear analysis and seismic design of such columns. Although extensive studies have been conducted on the monotonic axial behavior of small sized FRP-confined unreinforced concrete columns, there is a lack of research on FRP-confined RC columns and also their cyclic axial response. As a consequence, there is a lack of cyclic axial stress–strain models which can enable seismic response to be reliably simulated by numerical means. Due to such knowledge gaps, this study reports the results of thirty CFRP-confined large-scale unreinforced and RC circular columns subjected to monotonic and cyclic axial compression loading. The test results indicate that the overall shape of the stress–strain curves, the peak compressive stress and strain at failure, the unloading/reloading paths, and also the plastic strain of CFRP-confined concrete are influenced by the CFRP wrap and internal hoop steel reinforcement. On the basis of the experimental results, a cyclic stress–strain model for CFRP-confined circular RC columns is then proposed. The proposed model consists of three main components, namely (i) a monotonically ascending portion to describe the envelope curve, (ii) a polynomial equation to describe unloading paths, and (iii) a straight line to describe reloading paths. The influence of internal hoop reinforcement on the monotonic model, as well as the unloading and reloading responses is also considered. The accuracy of the proposed model is validated with the test data reported in this paper as well as other test results of relevance extracted from the open literature.

Study on cyclic deformation behavior of extruded Mg–3Al–1Zn alloy

Abstract Fatigue properties and cyclic deformation behavior of an extruded Mg–3Al–1Zn (AZ31) alloy were investigated by performing the strain-controlled low-cycle fatigue tests at room temperature. We believed that the total strain amplitude should be closely related to fatigue properties and cyclic damage process. This study aimed to investigate the deformation mechanism from the viewpoint of strain amplitude. We found that when the total strain amplitude increased from 0.3% to 0.4%, there was a noticeable change in compressive peak stress amplitude, which might correspond to the competition between twinning–detwinning process and dislocation slips. Microstructure and fracture morphology were investigated using optical microscopy and scanning electron micrograph. At the total strain of great amplitude, fracture surfaces were characterized by the striation-like features and dimple-like structures.

Effects of microstructure and shock loading conditions on the damage behavior of polycrystalline copper

A suite of plate-impact experiments have been conducted to determine the dominant factors in dynamic damage evolution in uniaxial strain tensile (spall) experiments. The first group of experiments addresses the effect of microstructure by using copper samples with varying grain sizes while maintaining similar loading conditions (peak compressive stress ∼ 1.5 GPa ). In a second set, the density of grain boundaries in copper samples and the compressive stress (∼ 1.6 GPa ) were held constant while the tensile loading characteristics were tailored by controlling the geometry of flyers and targets. For similar loading conditions, the damage fields were observed to depend on the grain size: void growth and coalescence were observed to dominate the damage behavior in samples with either small (30μm) or large grain size (200μm); whereas in samples with intermediate grain size (60 and 100μm), most of the damage was restricted to individual voids. For the second portion of the study the characteristics of the damage fields were observed to strongly depend on the characteristics of the tensile pulse. In this case, an increasing large plastic dissipation, in the form of grain misorientation, and more advanced stages of damage were observed in the samples deformed at lower tensile stress rates.

The effect of shockwave profile shape on dynamic brittle failure

The role of shock wave loading profile is investigated for the failure processes in a brittle material. The dynamic damage response of ductile metals has been demonstrated to be critically dependent on the shockwave profile and the stress-state of the shock. Changing from a square to triangular (Taylor) profile with an identical peak compressive stress has been reported to increase the “spall strength” by over a factor of two and suppress damage mechanisms. The spall strength of tungsten heavy alloy (WHA) based on plate impact square-wave loading has been extensively reported in the literature. Here a triangular wave loading profile is achieved with a composite flyer plate of graded density in contrast to the square-wave loading. Counter to the strong dependence in wave profile in ductile metals, for WHA, both square and triangle wave profiles the failure is by brittle cleavage fracture with additional energy dissipation through crack branching in the more brittle tungsten particles, largely indistinguishable between wave profiles. The time for crack nucleation is negligible compared to the duration of the experiment and the crack propagation rate is limited to the sound speed as defined by the shock velocity.

Response of Open Cell Aluminum Foams to Fully Reversed Cyclic Loading

The response of metal foams to fully reversed cyclic loading has been investigated much less than the response to tension-tension and compression-compression cyclic loads. This paper describes tests of open cell aluminum foams that are subjected to fully reversed cyclic loading. Three different damage measures are evaluated as candidates for tracking the damage state in the material. These measures and associated failure criteria track the peak tensile stress, the peak compressive stress, and the ratio of the prepeak tensile and compressive material stiffnesses in each cycle. The peak tensile stress measure and criterion gave the most stable results. Finally, the fatigue lifetime is modeled by using a statistical Weibull model.

The shear mechanical properties of diabetic and non-diabetic plantar soft tissue

Changes in the plantar soft tissue shear properties may contribute to ulceration in diabetic patients, however, little is known about these shear parameters. This study examines the elastic and viscoelastic shear behavior of both diabetic and non-diabetic plantar tissue. Previously compression tested plantar tissue specimens (n=54) at six relevant plantar locations (hallux, first, third, and fifth metatarsal heads, lateral midfoot, and calcaneus) from four cadaveric diabetic feet and five non-diabetic feet were utilized. Per in vivo data (i.e., combined deformation patterns of compression followed by shear), an initial static compressive strain (36–38%) was applied to the tissue followed by target shear strains of 50% and 85% of initial thickness. Triangle waves were used to quantify elastic parameters at both strain levels and a stress relaxation test (0.25s ramp and 300s hold) was used to quantify the viscoelastic parameters at the upper strain level. Several differences were found between test groups including a 52–62% increase in peak shear stress, a 63% increase in toe shear modulus, a 47% increase in final shear modulus, and a 67% increase in middle slope magnitude (sharper drop in relaxation) in the diabetic tissue. Beyond a 54% greater peak compressive stress in the third metatarsal compared to the lateral midfoot, there were no differences in shear properties between plantar locations. Notably, this study demonstrates that plantar soft tissue with diabetes is stiffer than healthy tissue, thereby compromising its ability to dissipate shear stresses borne by the foot that may increase ulceration risk.