Representative Loading Conditions Research Articles

Effects of Photovoltaic Module Materials and Design on Module Deformation Under Load

Quasi-static structural finite-element models of an aluminum-framed crystalline silicon photovoltaic module and a glass-glass thin-film module were constructed and validated against experimental measurements of deflection under uniform pressure loading. Specific practices in the computational representation of module assembly were identified as influential to matching experimental deflection observations. Additionally, parametric analyses using Latin hypercube sampling were performed to propagate input uncertainties related to module materials, dimensions, and tolerances into uncertainties in simulated deflection. Sensitivity analyses were performed on the uncertainty quantification datasets using linear correlation coefficients and variance-based sensitivity indices to elucidate key parameters influencing module deformation. Results identified edge tape and adhesive material properties as being strongly correlated to module deflection, suggesting that optimization of these materials could yield module stiffness gains at par with the conventionally structural parameters, such as glass thickness. This exercise verifies the applicability of finite-element models for accurately predicting mechanical behavior of solar modules and demonstrates a workflow for model-based parametric uncertainty quantification and sensitivity analysis. Applications of this capability include the assessment of field environment loads, derivation of representative loading conditions for reduced-scale testing, and module design optimization, among others.

Fatigue Strength of Highly Crosslinked Polyethylene in Total Ankle Arthroplasty

Category:AnkleIntroduction/Purpose:Highly crosslinked polyethylene (HXLPE) was developed for its superior wear properties in comparison to conventional polyethylene (CPE). The higher dose irradiation required for HXLPE may also cause embrittlement, which reduces fatigue resistance and leads to surface cracking or fracture of the polyethylene bearing. Concern over fatigue resistance has prevented widespread adoption of HXLPE for use in in total ankle arthroplasty (TAA). The aim of this study was to determine whether HXLPE has sufficient fatigue strength for total ankle arthroplasty under simulated physiologically relevant motion profiles and loading in the ankle.Methods:A bicondylar, semi-constrained HXLPE TAA design was subjected to 10 million cycles (Mc) of fatigue testing under loading conditions representative of a walking gait. Kinetics and kinematics of gait were incorporated into a computational model (Dassault Systemes / SIMULIA, Johnston, RI), for prediction of peak stresses on the HXLPE insert. Based on predicted peak stresses, worst case component size and loading configuration were identified. Ten samples were tested on a closed loop servohydraulic test frame (MTS Systems Corp., Minneapolis, MN) for 10Mc. Testing was conducted to a peak load of 5600 N (1259lbs), representing approximately 5 times body weight for a 240 lb individual. Following testing, all samples were evaluated for evidence of polyethylene fracture or surface cracking.Results:Peak stresses in the HXLPE insert occurred during heel off, closely corresponding to both peak axial force and dorsiflexion during gait. The smallest sized component had the highest polyethylene insert stresses, whereas larger sized components had more material to bear the same load, resulting in up to a 30% decrease in stress. All 10 specimens completed 10Mc of testing at 5 times body weight without fracture or surface cracking of the polyethylene insert.Conclusion:HXLPE has sufficient fatigue strength to withstand 10Mc of loading at 5 times body weight at the point of peak stresses during gait in total ankle arthroplasty, and therefore, may be mechanically strong enough to withstand the demands of the ankle. Further clinical evidence is necessary to determine if these results translate to adequate fatigue strength with clinical use of HXLPE.

A global-local fretting analysis methodology and design study for the pressure armour layer of dynamic flexible marine risers

In this paper, a global-local fretting design methodology for the pressure armour layer of flexible marine risers is outlined. This includes global dynamic riser analysis, geometrical and analytical sub-models and local nub-groove contact finite element analysis. Furthermore, a fretting test rig is developed and utilised to quantify coefficient of friction and wear coefficient under representative nub-groove loading conditions. The combination of the global-local computational methodology and experimental characterisation of pressure armour wire material allows for the development of running condition fretting maps. This identifies design criteria for critical riser global curvatures that are associated with minimum number of cycles to failure. The design methodology presented in this paper is applied to a realistic riser design study, using extreme sea-state loading conditions. In this case study, the predicted pressure armour fretting fatigue lives are found to be in the same range as the plain fatigue lives of the tensile armour layer.

Component-Level Finite Element Model and Validation for a Modern American Football Helmet

Epidemiological data and measurement of biomechanical data collected through physical experiments have contributed to the understanding of potential head injury risk in contact sports such as football. Further improvement of protective helmets requires repeatable conditions and detailed parametric studies that may be addressed in part using the Finite Element (FE) method. However, such an approach requires thorough experimentation and validation of the helmet materials and subcomponents, which previous studies do not fully address, prior to implementing these subcomponents in a full helmet model. Development of a modern football helmet FE model requires a bottom-up approach, focusing on material testing, constitutive models and subcomponent-level validation, which has not been fully addressed in the literature to date. Material samples were extracted from a modern football helmet including the helmet shell, energy-absorbing structures, comfort foam, and strap system. The subcomponents were tested across a range of quasi-static and high deformation rates relevant to football impact scenarios. FE models of the subcomponents were developed and validated, focusing on verification of material behaviour, representative loading conditions, and mesh convergence to achieve realistic responses and increase computational efficiency. Evaluation of the FE models comparing experimental with simulated responses, yielded good to excellent CORrelation and Analysis (CORA) ratings of 0.954–0.985, 0.931, 0.937–0.974, and 0.847–0.958 for the helmet shell, facemask, energy-absorbing structures, and comfort pads, respectively. The resulting validated subcomponent-level models provide an important foundation for integration into a full helmet model to ultimately optimize performance and reduce head injury.

Mechanical behavior of shark vertebral centra at biologically relevant strains

Cartilaginous shark skeletons experience axial deformation at the intervertebral joints, but also within the mineralized cartilaginous centrum, which can compress to between 3% and 8% of its original length in a free-swimming shark. Previous studies have focused on shark centra mechanical properties when loaded to failure; our goal was to determine properties when compressed to a biologically relevant strain. We selected vertebrae from six shark species and from the anterior and posterior regions of the vertebral column. Centra were X-radiographed to measure double cone proportion and apex angles, and were mechanically tested at three displacement rates to 4% strain. We determined the variation in toughness and stiffness of vertebral centra among shark species and ontogenetic stages, testing strain rates, and compared anterior and posterior regions of the vertebral column. Our results suggest that toughness and stiffness, which are positively correlated, may be operating in concert to support lateral body undulations, while providing efficient energy transmission and return in these swift-swimming apex predators. We analyzed the contribution of double cone proportion and apex angle to centra mechanical behavior. We found that the greatest stiffness and toughness were in the youngest sharks and from the posterior body, and there was significant interspecific variation. Significant inverse correlations were found between mechanical properties and double cone apex angle suggesting that properties can be partially attributed to the angle forming the double cone apex. These comparative data highlight the importance of understanding cartilaginous skeleton mechanics under a wide variety of loading conditions representative of swimming behaviors seen in the wild.

The development of a novel technique for small ring specimen tensile testing

The wide scale use of small specimens in routine testing programs could significantly reduce material resource requirements (factors of 10 are easily achievable). This is a major benefit to situations where there is not enough material to manufacture conventional, full-size specimens, such as first-stage gas turbine blade roots. However, limitations exist due to concerns over size effects, manufacturing difficulties, uncertainties related to the application of representative loading conditions and complex interpretation procedures of non-standard data. Due to these limitations, small specimen testing techniques have been mostly applied in ranking exercises and to determine approximate or simple material parameters such as Young’s modulus, minimum creep strain rate and fracture toughness. The small ring method is a novel, high sensitivity small specimen technique for creep testing that has been extended in the present work to the determination of tensile material properties. The main advantages of the small ring specimen are that it is self-aligning and has a large equivalent gauge length in comparison to other small specimens, resulting in much higher testing sensitivity. In the present work, this specimen type mimics conventional, full-size, monotonic testing, allowing for observations of elastic and plastic material response to be made. Wrought aluminium alloy 7175-T7153 small rings were tested at room temperature at 5 different loading (displacement) rates and the results compared to conventional, full-size, monotonic specimen equivalents. Finite element analysis was conducted in order to evaluate the equivalent gauge section and equivalent gauge length in the small ring specimen (which varied between circa 0.35–1.4 mm2 and 25–45 mm, respectively) to facilitate these comparisons. An analytical solution has also been derived in order to validate the finite element analysis.

The development of a novel small ring specimen tensile testing technique

The use of small specimens in routine testing would reduce resource requirements, however, limitations exist due to concerns over size effects, manufacturing difficulties, uncertainties related to the application of representative loading conditions, and complex interpretation procedures of non-standard data. Due to these limitations, small specimen testing techniques have been mostly applied for ranking exercises and to determine approximate or simple material parameters such as Young’s modulus, creep minimum strain rate and fracture toughness. The small ring method is a novel, high sensitivity small specimen technique for creep testing and has been extended in the present work for the determination of tensile material properties. Wrought aluminium alloy 7175-T7153 was tested at room temperature at 5 different loading rates. Finite element analysis was completed to evaluate the equivalent gauge section and equivalent gauge length in order to compare uniaxial tensile testing results and small ring specimen tensile testing results. An analytical solution has also been derived in order to validate the finite element analysis. It was discovered that the finite element analysis model was suitable, validated by both experimental results and analytical solution as well as that small ring specimens can be used to acquire same stress/strain data as uniaxial specimens.

A new approach to the internal thermal management of cylindrical battery cells for automotive applications

Conventional cooling approaches that target either a singular tab or outer surface of common format cylindrical lithium-ion battery cells suffer from a high cell thermal resistance. Under an aggressive duty cycle, this resistance can result in the formation of large in-cell temperature gradients and high hot spot temperatures, which are known to accelerate ageing and further reduce performance. In this paper, a novel approach to internal thermal management of cylindrical battery cells to lower the thermal resistance for heat transport through the inside of the cell is investigated. The effectiveness of the proposed method is analysed for two common cylindrical formats when subject to highly aggressive electrical loading conditions representative of a high performance electric vehicle (EV) and hybrid electric vehicle (HEV). A mathematical model that captures the dominant thermal properties of the cylindrical cell is created and validated using experimental data. Results from the extensive simulation study indicate that the internal cooling strategy can reduce the cell thermal resistance by up to 67.8 ± 1.4% relative to single tab cooling, and can emulate the performance of a more complex pack-level double tab cooling approach whilst targeting cooling at a single tab.

Validation of a new computational 6-DOF knee simulator during dynamic activities

A new six-degree-of-freedom (6-DOF) joint simulator has recently been developed which facilitates testing of implants under more realistic loading conditions than has been possible previously. However, typical wear testing can be very time-consuming, taking weeks or months to complete. A validated computational model is an ideal complement to these types of long-running tests. In this study, a computational counterpart to the new 6-DOF joint simulator was developed and validated. Total knee replacement components were evaluated in both physical and computational simulations, and joint mechanics were compared between the experiment and the model. Kinematic comparisons were carried out for two total knee replacement designs, under loading conditions representative of three different activities of daily living: deep knee bend, gait, and stepdown. The model accurately reproduced the motions obtained in the physical simulator, and appropriately differentiated between activities and between implant designs. Root-mean-square differences in anterior-posterior translations and internal-external rotations were less than 1.7mm and 1.4°, respectively, for both implant designs and all three dynamic activities. Contact area, and peak and average contact pressure predicted by the model matched experimental measurements with a root-mean-square accuracy of 20mm2, 9MPa, and 1MPa, respectively. The computational model of the 6-DOF joint simulator will be a key tool in efficient evaluation of implant mechanics under loading conditions representative of the in vivo environment. These simulations may be used directly in comparison of devices, or may aid in facilitating optimal usage of the physical simulator through determining which activities and/or loading conditions best address specific clinical or design issues, for example, development of worst-case loading profiles for wear testing.

Quantification of the lateral forces in concrete sleeper fastening systems

Consistent increases in cumulative freight tonnages, combined with the move towards increased higher-speed intercity passenger rail operation, have placed greater demands on North American railroad infrastructure. Concrete sleepers and fastening system components are known to fail at a wide range of life cycle intervals when subjected to demanding loading environments. Such failures can cause track geometry defects, require repetitive maintenance procedures, and present critical engineering challenges. Rail seat deterioration, the degradation of the concrete material beneath the rail, has been identified through a survey of North American Class I railroads to be the most-critical engineering challenge for concrete sleepers. Shoulder/fastener wear or fatigue was identified by the same survey as the second-most-critical engineering challenge related to concrete sleepers. Lateral forces transferred through the fastening system are thought to be a primary cause of degradation of insulators. The objective of this study is to quantify the demands on the insulator through analysis of the transfer of lateral wheel loads into the fastening system by measuring the magnitude of the lateral forces entering the shoulder, a component of the fastening system adjacent to the insulator. The lateral load evaluation device (LLED) was developed at the University of Illinois in Urbana Champaign to quantify these forces. Data captured by the LLED will assist the rail industry in moving towards the mechanistic design of future fastening systems, by quantifying the lateral forces in the fastening system under representative loading conditions. Information gained through this study will also lead to a better understanding of the frictional forces at key interfaces in the fastening system. Preliminary results show that the transfer of lateral wheel loads into the fastening system is highly dependent on the magnitude of the lateral wheel loads and the frictional characteristics of the fastening system.

Calibration of Gurson-type models for porous sheet metals with anisotropic non-quadratic plasticity

The growth and coalescence of voids in sheet metals are not only the main active mechanisms in the final stages of fracture in a necking band, but they also contribute to the forming limits via changes in the normal directions to the yield surface. A widely accepted method to include void effects is the development of a Gurson-type model for the appropriate yield criterion, based on an approximate limit analysis of a unit cell containing a single spherical, spheroidal or ellipsoidal void. We have recently [2] obtained dissipation functions and Gurson-type models for porous sheet metals with ellipsoidal voids and anisotropic non-quadratic plasticity, including yield criteria based on linear transformations (Yld91 and Yld2004-18p) and a pure plane stress yield criteria (BBC2005). These Gurson-type models contain several parameters that depend on the void and cell geometries and on the selected yield criterion. Best results are obtained when these key parameters are calibrated via numerical simulations using the same unit cell and a few representative loading conditions. The single most important such loading condition corresponds to a pure hydrostatic macroscopic stress (pure pressure) and the corresponding velocity field found during the solution of the limit analysis problem describes the expansion of the cavity.However, for the case of sheet metals, the condition of plane stress precludes macroscopic stresses with large triaxiality or ratio of mean stress to equivalent stress, including the pure hydrostatic case. Also, pure plane stress yield criteria like BBC2005 must first be extended to 3D stresses before attempting to develop a Gurson-type model and such extensions are purely phenomenological with no due account for the out- of-plane anisotropic properties of the sheet. Therefore, we propose a new calibration method for Gurson- type models that uses only boundary conditions compatible with the plane stress requirement. For each such boundary condition we use a spectral method to solve the limit analysis problem, using as spectral basis a newly developed Mie decomposition of incompressible velocity fields for ellipsoidal cells with confocal ellipsoidal voids, extending the well-known Lee and Mear family corresponding to the spheroidal axisymmetric case [1]. We thus obtain a series of points located on the Gurson-type yield surface and their corresponding normal directions. These points are used as input to some enhanced parameter identification method developed for anisotropic yield criteria [1] to determine the calibration of the Gurson-type models. We finally use these newly calibrated Gurson-type models to evaluate forming limits for porous sheet metals.

Modelling of fretting in the pressure armour layer of flexible marine risers

This paper presents a computational methodology for frictional contact mechanics of the pressure armour layer in flexible risers. This will allow, for the first time, quantification of key fretting variables, such as contact pressure, relative slip and sub-surface stresses in this complex geometry, under representative loading conditions. Fatigue lives are calculated using the 3-dimensional critical plane Smith–Watson–Topper multiaxial fatigue parameter. It is shown that COF has a significant effect on predicted trailing-edge tensile stresses in the pressure armour layer and, hence on fretting crack initiation in risers. It is also shown that operating pressure and bending-induced axial displacement significantly affect predicted crack initiation. These results will facilitate representative fretting wear and fretting fatigue testing of pressure armour layer material.

Comparative evaluation of structural integrity for ITER blanket shield block based on SDC-IC and ASME code

The ITER blanket Shield Block is a bulk structure to absorb radiation and to provide thermal shielding to vacuum vessel and external vessel components, therefore the most significant load for Shield Block is the thermal load. In the previous study, the thermo-mechanical analysis has been performed under the inductive operation as representative loading condition. And the fatigue evaluations were conducted to assure structural integrity for Shield Block according to Structural Design Criteria for In-vessel Components (SDC-IC) which provided by ITER Organization (IO) based on the code of RCC-MR.Generally, ASME code (especially, B&PV Sec. III) is widely applied for design of nuclear components, and is usually well known as more conservative than other specific codes. For the view point of the fatigue assessment, ASME code is very conservative compared with SDC-IC in terms of the reflected Ke factor, design fatigue curve and other factors. Therefore, an accurate fatigue assessment comparison is needed to measure of conservatism. The purpose of this study is to provide the fatigue usage comparison resulting from the specified operating conditions shall be evaluated for Shield Block based on both SDC-IC and ASME code, and to discuss the conservatism of the results.

An antiplane shear crack moving in one-dimensional hexagonal quasicrystals

An investigation is presented of an antiplane shear strip crack subjected to representative general non-constant crack-face loading conditions which is moving uniformly in one-dimensional hexagonal quasicrystals, using an extended technique of continuous dislocation layers. Readily-calculable explicit closed-form representations are determined and discussed for the components of the phonon and phason stress fields created throughout the media. Illustrative numerical results are presented graphically. As a special case, the corresponding expressions are deduced explicitly for a non-uniformly loaded stationary crack.

Predicting the behaviour of coal wash and steel slag mixtures under triaxial conditions

The effective reuse and recycling of granular waste materials, namely coal wash (CW) and basic oxygen steel slag (BOS), are economically beneficial and environmentally sustainable. Nevertheless, due to the heterogeneity of these granular waste materials, the ultimate adoption of CW and BOS as structural fills must be supported by constitutive relationships capable of accurately describing the stress–strain behaviour under representative field loading conditions. In this paper, a critical state surface generalized plasticity model is presented, and its predictive capability using an explicit set of soil parameters is demonstrated for drained triaxial compression tests.

Development of structural and material clavicle response corridors under axial compression and three point bending loading for clavicle finite element model validation

Clavicle injuries were frequently observed in automotive side and frontal crashes. Finite element (FE) models have been developed to understand the injury mechanism, although no clavicle loading response corridors yet exist in the literature to ensure the model response biofidelity. Moreover, the typically developed structural level (e.g., force–deflection) response corridors were shown to be insufficient for verifying the injury prediction capacity of FE model, which usually is based on strain related injury criteria. Therefore, the purpose of this study is to develop both the structural (force vs deflection) and material level (strain vs force) clavicle response corridors for validating FE models for injury risk modeling. 20 Clavicles were loaded to failure under loading conditions representative of side and frontal crashes respectively, half of which in axial compression, and the other half in three point bending. Both structural and material response corridors were developed for each loading condition. FE model that can accurately predict structural response and strain level provides a more useful tool in injury risk modeling and prediction. The corridor development method in this study could also be extended to develop corridors for other components of the human body.

Response of polyurea-coated flat composite plates to underwater explosive loading

An experimental and numerical study has been conducted to evaluate the underwater blast response of E-Glass/epoxy composite plates with polyurea coatings. The goal of the study is to determine the effects of these elastomeric coatings on the dynamic response of the plates, specifically the influence of coating thickness, location, and plate natural frequency. The composite material is a 0°/90° biaxial layup and the coatings are applied to either the loaded or non-loaded faces. A conical shock tube facility which produces shock loading conditions representative of the underwater detonation of an explosive charge is used to impart the shock loading to the plates during the experiments. The transient response of the plates is recorded using a three-dimensional (3D) digital image correlation system, consisting of high-speed photography and specialized post processing software. Computational models of the experiments are developed using the LS-DYNA finite element code. The simulations are shown to have a high level of correlation to the experimental data in terms of center point displacements and full field deformation profiles. Additional parametric studies using the correlated model show that the transient response of the composite plates is improved with increasing coating thickness, and that polyurea coatings located on the back face of the panels provide better performance than when located on the loaded surface.

Multiaxial cyclic viscoplasticity model for high temperature fatigue of P91 steel

This paper presents a novel multiaxial, cyclic viscoplasticity material model for high temperature low cycle fatigue of P91 power plant steel. The model incorporates mechanisms-based variable strain-rate sensitivity and the key high temperature cyclic deformation phenomena of cyclic softening and non-linear kinematic hardening. The model has been calibrated to accurately represent the cyclic high temperature constitutive behaviour of ‘as received’ P91 steel. Details on the material Jacobian, with the consistent tangent stiffness for finite element implementation, are presented. The multiaxial implementation is applied to a notched specimen under strain-controlled loading at 600°C and a thin walled pipe under representative pressurised thermomechanical fatigue loading conditions. It is shown that the model for variable strain-rate sensitivity of the present paper predicts significantly different Coffin–Manson notch fatigue life compared to the Chaboche power law model. Ratchetting is shown to be a key candidate failure mechanism for next generation thermomechanical power plant loading conditions, for thin walled pressurised pipes.

Rheological properties of soft-glassy flows from hydro-kinetic simulations

Based on numerical simulations of a lattice kinetic model for soft-glassy materials, we characterize the global rheology of a dense emulsion-like system, under three representative load conditions: Couette flow, time-oscillating Strain and Kolmogorov flow. It is found that in all cases the rheology is described by a Herschel-Bulkley (HB) relation, , with the yield stress largely independent of the loading scenario. A proper rescaling of the HB parameters permits to describe heterogeneous flows with space-dependent stresses, based on the notion of cooperativity, as recently proposed to characterize the degree of non-locality of stress relaxation phenomena in soft-glassy materials.

Moment-Rotation Behavior of Force-Based Plastic Hinge Elements

The moment-rotation behavior of force-based frame elements is expressed as a function of plastic hinge length and moment-curvature parameters for two types of plastic hinge integration under the representative loading condition of antisymmetric bending. For modified Gauss-Radau hinge integration, there is a unique relationship between the resulting moment-rotation hardening ratio and parameters defining the plastic hinge length and moment-curvature hardening ratio. For two-point Gauss-Radau hinge integration, the spread of yielding across the hinge regions leads to a multilinear moment-rotation response, for which a secant approximation of the hardening stiffness is directed to a target plastic rotation. An example application demonstrates that significantly unconservative assessments of lateral load-carrying capacity can be attained if modeling parameters for plastic hinge length and moment-curvature strain hardening are not calibrated to account for the discrepancy between moment-curvature and moment-rotation behavior of an element.