The stress behavior in adhesive laminated cantilever beams subjected to impact loadings is analyzed using three-dimensional finite-element method (FEM) in the elastic region. The stress wave propagation and the stress distribution at the interfaces are examined. The effects of Young’s modulus of adherends, adhesive, the adherend thickness and the number of layers on the stress wave propagation at the interfaces are clarified. The following results are obtained. The maximum principal stress (σ 1 ) is maximal at the adhesive interfaces. It is found that the maximum principal stress (σ 1 ) at the adhesive interface increases as the Young’s modulus of the upper adherends increases. The maximum principal stress (σ 1 ) at the adhesive interface increases as Young’s modulus of the adhesive increases. The maximum principal stress (σ 1 ) at the adhesive interface decreases as the thickness of the adherend to which an impact load is applied increases. It is seen that the maximum principal stress (σ 1 ) increases as number of layers increases. Experiments were carried out to measure the strain response of adhesive laminated cantilever beam using strain gauges. A fairly good agreement is seen between the analytical and experimental results.

A bolted joint is subjected to high stress concentration at the thread root because of its complicated geometry involved. Plastic regions are produced around the bottom of thread root, even under relatively low bolt axial force. It is predicted that the plastic deformation thus produced might affect such important mechanical behaviors of bolted joint as load distributions along threads, the relationships between bolt axial force and angle of nut rotation, etc. In many practical applications, bolts are tightened with considerably high clamping force, especially when tightening critical structures. Thus, it is considered that numerical studies taking the effects of plastic deformation into account are extremely important. However, many previous studies have only dealt with a bolted joint under pure tension. When tightening bolted joints with torque control shear stresses are generated in addition to the tensile stress due to bolt clamping force. In this study, mechanical behaviors of bolted joint during tightening with torque control are analyzed by FEM as an elasto-plastic contact problem, where three-dimensional analysis is conducted employing two dimensional model with each node having three degrees of freedom.

The stresses of joints combining the bonding force of adhesives with the clamping force of bolts is analyzed using axisymmetrical theory of elasticity and FEM, when an internal pressure is applied to the combination joint in which two pipe flanges are clamped together by bolts and nuts with an initial clamping force after being joined by anaerobic sealant. The anaerobic sealant is applied at the interfaces partially instead of formed gaskets in pipe flange connections. In the numerical calculations, the effect of the bonding area and position and Young’s modulus of sealant (epoxy adhesive) on the contact stress at the interfaces are clarified. In addition, using the interface stress distribution, the strength of the combination joint is predicted. Experiments are performed and the analytical results are consistent with the experimental results concerning the variation in axial bolt force and the strength of combination joints. It is found that the joint strength changes as the bolt pitch circle diameter, the bonding position and the area, the initial clamping force and the adhesive material properties change. Furthermore, it is seen that the sealing performance of such combination joints in which the interfaces are bonded partially is improved over that of pipe flange connection with metallic gaskets.

Bolted joints with gaskets have been designed empirically, and the sealing performance is not made clear by theoretical analyses because the contact stress distribution between the gasket and the flanges are not clarified when an internal pressure is applied to the joint. The present paper, discusses the distribution of contact stresses in the bolted joints fastened with tap bolts, when a clamped part with a gasket is the cover of a pressure vessel and is a circular flange. The distribution of contact stresses is analyzed as a three-body contact problem, using the three-dimensional theory of elasticity. Moreover, the contact stress is measured by means of ultrasonic waves. In addition, the load factor (the ratio of an increment of the axial bolt force to an external load) and the maximum stress caused in bolts are analyzed taking into account the bending moment. For verification, experiments are carried out, and the analytical results are found in fairly good agreement with the experimental ones. It was found that the sealing performance was improved when Young’s modulus of the gaskets was decreased and the gasket thickness was increased.

This paper presents comprehensive tire/pavement contact-stress models based on the Artificial Neural Networks developed by the authors at the Pennsylvania Transportation Institute and Applied Research Laboratory of the Pennsylvania State University. These models represent the first mathematical representation of measured, vertical contact stress at wide ranges of vertical loads and inflation pressures for two types of tires. The Developed ANN model has the capabilities to generate complex stress distribution patterns under a tire at any given load and inflation pressure for a specific tire type used for the ANN training. The information given here is considered to be an important contribution to the ongoing efforts to improve tire/pavement contact stress modeling and analysis. The neural network representation of a tire contact stress distribution is denoted as “Neuro-Patch Model”. The neural network models have been trained using precisely measured, three-dimensional contact-stress distribution patterns obtained from low speed rolling tire tests conducted by the University of California at Berkeley. This data has been supplied by the Federal Highway Administration (FHWA). In this study two types of tires, namely a 11R22.5 Radial-Ply and a 10.00 × 20 Bias-Ply truck tire, were modeled at different inflation pressures ranging from 520 kPa to 920 kPa and vertical loads ranging from 26 kN to 56 kN.

During long duration space flight, astronauts must exercise to prevent bone demineralization. Exercises are used as countermeasures to the bone mineral loss. The effectiveness of the countermeasures is closely related to the mechanical stress developed during the exercises. A finite element model of the human femur was developed to determine the stress distribution during weight bearing. The model was developed using serial, transverse magnetic resonance images. The finite element analysis performed on the femur model showed an area of high stress in the femoral neck of approximately 1,200 psi. The highest stress seen in the model was approximately 2,000 psi. This information will then be used to evaluate the proposed exercises to be used as countermeasures.

Rupture of abdominal aortic aneurysm (AAA) occurs when the wall stress acting on the dilated aortic wall exceeds the strength of the tissue. Therefore, accurate estimation of the wall stress distribution in AAA may be a clinically useful tool to predict their rupture. A majority of AAA contains a laminated, stationary, intraluminal thrombus (ILT) (Harter et al., 1982). Previous investigations have shown that ILT may significantly alter the wall stress acting on AAA (Inzoli et al., 1993; Mower et al., 1997; Stringfellow et al., 1987; Vorp et al., 1998; Di Martino et al., 1998). However, all of those studies used a simplified linear elastic model for ILT. This is inappropriate and can lead to inaccuracies since both AAA wall and contained ILT undergo large deformation during the cardiac cycle (Vorp et al., 1996). Therefore, to accomplish accurate stress analysis of AAA, appropriate constitutive models for both the wall and ILT are necessary. Our group has previously proposed a finite strain constitutive model for the AAA wall (Raghavan et al., in press). The purpose of this work was to derive a more suitable constitutive model and the associated mechanical properties for the ILT within AAA.

The finite element (FE) method has been used in orthopaedic biomechanics to investigate the fixation role of different design parameters in total knee replacement (TKA). Previous FE model studies used 2D, axisymmetric and 3D models to represent the geometry while neglecting many essential features. They simulated the bone-implant interface as frictionless, perfectly bonded or with idealized Coulomb’s friction model. The model of screws and posts have also been neglected altogether or inadequately considered in these studies. To overcome these limitations, the objective of the present study was set to develop a detailed 3D FE model of the knee bone-implant structure including all the interacting components in an immediate postoperative period without bony ingrowth to predict the micromotion at the bone-implant interface and stress distribution within the bone and the polyethylene insert.

Vascular stents are being used in increasing numbers to correct arterial flow limiting disorders. Although data exist on the in vivo performance of these devices, comparatively little is known about how these devices affect the arterial mechanical environment. The long-term success of stenting is very likely affected by the blood flow patterns and artery wall stresses that follow stent placement. This study was undertaken to identify the mechanical environment in stented arteries and to propose a stent design that minimizes the “mechanical trauma” of stent implantation. A series of pulsatile flow visualization experiments were performed with a Johnson & Johnson Palmaz/Schatz stent inserted in a straight compliant tube. A flow loop was constructed that was capable of applying a physiologic pulsatile flow indicative of conditions in the femoral or coronary arteries. The results showed that this stent design creates complex flow patterns including large-scale vortices, and that these patterns are caused by the compliance mismatch between the stented vessel and adjacent unstented vessel. The compliance mismatch also would be expected to create abnormal stress concentrations in the artery wall near the ends of the stent. A simplified model of an artery was constructed to estimate the stress in the artery wall. The stent/artery structure was assumed to be an axisymmetric thin shell made of a linear elastic, orthotropic material that undergoes small deformations. The stent diameter was assumed to be equal to the artery systolic diameter. The stresses were estimated under diastolic pressure, when the deflection of the artery due to the presence of the stent is greatest. It was found that the circumferential and axial stresses at the ends of the stent were 2 to 3 times higher than the stress far from the stent. Based on these mechanical studies, a new stent design was proposed that provides a smooth transition in compliance at the proximal and distal ends of the tube. Flow visualization studies with this new stent indicate that the flow disturbances are greatly reduced with this new design. The transition zone was incorporated into the shell model to estimate the artery wall stresses induced by this new model. It was found that the stress concentration was reduced by as much as 36% from the rigid stent value. These studies demonstrate the potential complexity of flow in stented arteries and provide some recommendations for optimizing stent design from a biomechanical point of view. This work was supported in part by a Linkage Grant from NATO.

Linear finite element analysis (fea) was performed to determine stress concentration factors for the threads and the bolt head fillet in a bolted connection. The fea models consisted of axisymmetric representations of a bolt and two circular steel plates each 20 mm in thickness. The bolts studied were 8, 12, 16, 20, and 24 mm diameter grade 10.9 metric bolts with the standard M thread profile. The threads were modeled at both the minimum and maximum allowable depths. The fillet between the bolt shank and bolt head connection was modeled at its minimum radius. Each bolt was loaded to its proof strength. A comparison is made to stress concentration factors typically used in bolted connection design. Stress concentration factors in the head fillet were 3.18, 3.23, 3.63, 3.58, and 3.90 for the 8, 12, 16, 20, and 24 mm bolts, respectively. Thread stress concentration factors were highest in the first engaged thread and decreased in each successive thread moving toward the end of the bolt. Stress concentration factors for the shallow thread models ranged from 1.17 to 4.33, 0.87 to 4.32, 0.83 to 4.67, 0.87 to 4.77, and 0.82 to 4.82 for the 8, 12, 16, 20, and 24 mm bolts, respectively. Likewise, stress concentration factors for the deep thread models ranged from 1.18 to 4.80, 0.88 to 4.80, 0.78 to 5.12, 0.83 to 5.17, and 0.82 to 5.22 for the 8, 12, 16, 20, and 24 mm bolts, respectively.

In aging aircraft the synergetic interaction between corrosion and fatigue has been shown to impact the life expectancy of aluminum alloys. The objective of this study was to quantify the effects of corrosion, in terms of mass loss, on the static strength and fatigue life of 7075-T6-aluminum alloy. This was an experimental study conducted on samples with laboratory-controlled corrosion of varying mass loss levels at their mid-surface on one side. The specimens were covered with special masking material to allow corrosion only in the desired area. Both fatigue life and the ultimate tensile strength of the specimens were observed to drop significantly with small amounts of mass loss (less than 5%). After the initial decrease the UTS was observed to decrease linearly with additional mass-loss. The fatigue life of the specimens decreased significantly with additional mass loss. The topology of the pits, and the related subsurface damage hinted at existence of areas of high stress concentration resulting in the immediate reduction of UTS and fatigue life of the specimens.

Standard methods of indentation analysis use a beam theory solution to obtain an overall load-displacement relationship and then a Hertzian contact solution to calculate local stresses under the indenter. However, these techniques are only applicable in a fairly limited class of problems: previous modeling efforts have shown that the stress distribution in the region of contact will differ significantly from a Hertzian one when the contact length exceeds the thickness of the beam. In such cases, point contact can no longer be assumed and Hertzian relations are not valid. The indentation model developed herein is an improvement over current GLOBAL/LOCAL approaches in that it uses an elasticity solution to establish the load-displacement relationship at the contact site. The solution technique is applied to two end conditions: (1) simple supports, and (2) fixed ends. Superposition of appropriate elasticity expressions results in systems of Fredholm integral equations of the second kind that are solved numerically. Maximum contact stresses are obtained and compared with the predictions of the previous GLOBAL/LOCAL model. The validity of the solutions presented is assessed by comparing the results obtained to the predictions of modified beam theory solutions.

In an effort to investigate the mechanical properties of shape memory alloy (SMA) fiber reinforced composites, the stress distribution due to the phase change in the fiber is examined. We study a simple model involving a single infinite fiber embedded in an infinite elastic matrix. A portion of the fiber is allowed to undergo uniform phase transformations along the axial direction while the matrix remains linearly elastic. Under perfect bonding condition, the deformation of the fiber forces the matrix to deform in the elastic regime in order to accommodate the transformation strain. To simplify the analysis, the elasticity of the fiber is ignored. The problem is formulated as axisymmetric deformations for the matrix with a piecewise linear boundary condition at the interface with the fiber as a result of the phase transformation in the fiber. The exact elasticity solution (in integral form) to this problem is found using Love’s stress function and Fourier transform. The normalized forms of the solution are presented. The asymptotic behaviors of the stress distributions near the phase boundary are analyzed in details. The characteristics of the singularities near the phase boundary are obtained for this model. Numerical evaluations are also performed to obtain the distributions of the displacements, the strains, and the stresses in the matrix. In particular, the shear load transfer profiles along the interface are obtained for various aspect ratios of the transformed region.

Numerous studies have confirmed a correlation between the restored tooth fracture and the cavity design parameters. Improper geometric design of cavity could increase the unfavorable stresses of remaining tooth structure and cause fracture. However, the quantitative guideline for cavity preparation is unclear. This study developed an automatic mesh generation tool and employed finite element method to examine the stress distribution with different cavity depth designs in class II MOD restoration. The results indicated that for deeper cavity designs the unfavorable stress gradient was evident, therefore, the existence of a pulpal wall is essential.

Three-dimensional finite element analyses (FEA) of an elastic, single rivet-row, aluminum alloy lap joint are presented. The effects of rivet geometry (countersinking), rivet material and interfacial friction coefficient are examined. Interference and lateral clamping are not treated. Panels loaded in tension with vacant, tapered holes are also examined. Load transfer through the joint, the joint compliance, rivet-tilt, the local slips at rivet-panel and panel-panel interfaces, contact pressures and local stresses are evaluated. Relations between these features and the contact and bending driven stress concentration are clarified. The work shows that the stress concentration factor, rivet-panel slips, peak stresses, contact pressures and rivet deformation are all related, and increase with the severity of the countersink. Panel bending, rivet tilt and countersinking introduce large, out-of-plane stress gradients and shift the peak stresses to the interior surface of the countersunk panel. The results demonstrate the importance of out-of-plane distortions in accounting for the behavior of the riveted lap joints. Three opportunities are identified for improving lap joint performance without increasing the weight.

The concept of stress-induced cervical lesions has been discussed widely in recent years. In this study, a three-dimensional finite element model was established to analyze the stress distribution at cervical region and evaluate the stresses on the interface of different restorative materials. The results indicated that tensile stress might be the major cause for tooth cervical lesion. For different restorative materials, the elastic modulus was not the key issue in premature loss of restorative material. The bonding strength between the restorative material and lesions could be the important factor for the retention failure.

A finite element analysis (FEA) model of the interaction of a nut and bolt was used to investigate the effects of sliding, friction, and yielding in a bolted connection. The finite element model was developed as a two-dimensional, axisymmetric system, which allowed the study of axial and radial loading and displacements. This model did not permit evaluation of hoop or torsional effects such as tightening or the helical thread form. Results presented in this paper include the distribution of load between consecutive threads, the relative sliding along thread faces, and the stress distribution and regions of yielding in the model. Finally, a comparison to previous, linear analysis work and to published experimental data is made to conclude the paper.

Electrostatically positioned droplets are very useful for the fundamental study of solidification phenomena and the measurement of thermal physical properties. This paper descries a numerical analysis of surface deformation and surface tension driven flows in electrostatically positioned droplets in microgravity. The analysis is based on a fully coupled boundary element and finite element solution of the Maxwell equations, the Navier-Stokes equations and the energy balance equation. Results show that an applied electrostatic field results in a nonuniform electric stress distribution along the droplet surface, which, combined with surface tension, causes the droplet to deform into an ellipsoidal shape in microgravity. Laser heating induces a non-uniform temperature distribution in the droplet, which in turn produces Marangoni convection in the droplet. It is found that the viscous stress contribution to the deformation is small for a majority of cases. Also, a higher temperature gradient produces a stronger Marangoni convection in droplets with higher melting points that require more laser power. The internal recirculating flow may be reduced by more uniform laser heating. During the undercooling of the droplet, both temperature and fluid flow fields evolve in time such that the temperature gradient and the tangential velocities along the droplet surface subside in magnitude and reverse their directions.

Arterial disease most often can be classified in one of two categories — aneurysm and atherosclerosis. Interestingly enough these diseases affect the artery only at certain locations rather than the whole organ, i.e., the diseases have predilection for certain sites. Furthermore, some of the sites are common to both the diseases and at some sites, not so infrequently, the diseases occur together one preceding the other.

Three-dimensional finite element analysis of an elastic, double rivet-row, aluminum alloy lap joint with countersunk, aluminum and steel rivets, is presented. Relations between the connection compliance, rivet deformation, peak contact pressures and slip amplitudes, in the absence of interference and clamp-up, are described. Analysis of a connection with non-countersunk rivets is presented in a companion paper. The trends seen in the results are similar to those obtained with non-countersunk rivets, although the peak stress concentrations in the present case are much higher. A superposition approach for estimating stress concentration factors in the panels of multi-row riveted connections with standard or countersunk rivets is presented.