The application of composite material in structures can not only lower the component weight but also improve the system performance through its tailorable thermal and mechanical properties. However, because of the harsh environmental conditions that such structures may encounter during operation, the successful applications of such structures cannot be realized without appropriate techniques for their structural integrity evaluation. In this study, composite cylindrical structures consisting of composite and steel layers are being evaluated with X-ray diffraction technique and various ultrasound techniques. First, X-ray diffraction technique was applied for the quantitative determination of the residual stress in the steel layer. The influence of composite layer on the stress distribution was analyzed and how such residual stress study will improve the performance of the structure was discussed. Then various ultrasound techniques were applied for the detection of various defects, such as the defects at the surface and subsurface of inner steel layer, the different types of defects in the outer composite layer, and the defect, which is the most critical one, at the interface of steel/composite layer. During ultrasound evaluation, the composite material may not only increase the ultrasound attenuation but also change ultrasound traveling direction, and this can make the inspection more challenging. Theoretical calculations were carried out for the optimization of experimental parameters such as ultrasound frequency, incident angle, and focused ultrasound field calculation and so on. The limitations of ultrasound technique and the potential of other non-destructive techniques were also discussed according to experimental results.

Health monitoring devices using a strain sensor, which shows high sensitivity and large deformability, are strongly demanded due to further aging of society with fewer children. Conventional strain sensors, such as metallic strain gauges and semiconductive strain sensors, however, aren’t applicable to health monitoring because of their low sensitivity and deformability. In this study, fundamental design of area-arrayed graphene nano-ribbon (GNR) strain senor was proposed in order to fabricate next-generation strain sensor. The sensor was consisted of two sections, which are stress concentration section and stress detecting section. This structure can take full advantage of GNR’s properties. Moreover, high quality GNR fabrication process, which is one of the important process in the sensor, was developed by applying CVD (Chemical Vapor Deposition) method. Top-down approach was applied to fabricate the GNR. At first, in order to synthesize a high-quality graphene sheet, acetylene-based LPCVD (low pressure chemical vapor deposition) using a closed Cu foil was employed. After that, graphene was transferred silicon substrate and the quality was evaluated. The high quality graphene was transferred on the soft PDMS substrate and metallic electrodes were fabricated by applying MEMS technology. Area-arrayed fine pin structure was fabricated by using hard PDMS as a stress-concentration section. Finally, both sections were integrated to form a highly sensitive and large deformable pressure sensor. The strain sensitivity of the GNR-base sensor was also evaluated.

Several types of implants, plates, and screws have been developed for corresponding bone fractures at different sites. To understand the mechanical behavior of a bone plate and to provide surgeons with suggestions for selecting screw positions, this study aimed to create an APP to provide pre-surgical planning using a computed tomography (CT)-based finite element model. This model was validated using a compression test of synthetic sawbones. Furthermore, the specific APP was established using the COMSOL application builder to calculate the stress and strain of the implant under different screw positions. This APP reveals how the number and location of screws affect the stress distribution of the implant. It can provide clinicians with preliminary reference information before surgery.

In the clinical application, the mechanical stimulation against the damaged brain tissue is adopted as the kinesitherapy for the nerve regeneration. Nevertheless, the fundamental mechanism to repair the damaged nerve cell has not been revealed yet. Recently, the cyclic stretch stimulation has been reported as the efficacious treatment method to enhance the axonal extension for regenerative therapy of injured nerve cell. Therefore, we try to develop a new cellular automaton (CA) finite element (FE) hybrid method to predict the axonal extension and nerve network generation, which can evaluate the effect of stretch stimulation on the cell body, axon and dendrites. In the FE results, the stress concentration occurred at the junction of the axon and cell body. The maximum stress value in the axon was 8.2 kPa which is about twice as large as that of the cell body. CA adopted to predict the morphological evolution of nerve cells under the mechanical stimulation. It was confirmed that the stress affects to accelerate the axonal extension as experimentally suggested. As a result, our CAFE can be employed to simulate the axonal extension and generation of nerve network system under the condition of extra cellular mechanical stimulation.

Due to high stiffness/weight ratio, composite materials are widely used in aerospace applications such as motor case of rockets which can be regarded as a pressure vessel. The most commonly used method to manufacture the pressure vessels is the wet filament winding. However, the mechanical performance of a filament wound pressure vessel directly depends on the manufacturing process, manufacturing site environmental condition and material properties of matrix and fiber. The designed ideal pressure vessel may not be manufactured because of the mentioned issues. Therefore, manufacturing of filament wound composite structures are based on manufacturing experience and experiment. In this study, the effect of layer-by-layer thickness and fiber volume fraction variation due to manufacturing process on the mechanical performance was investigated for filament wound pressure vessel with unequal dome openings. First, the finite element model was created for designed thickness dimensions and constant material properties for all layers. Then, the model was updated. The updated finite element model considered the layer-by-layer thickness and fiber volume fraction variation. Effects of the thickness and fiber volume fraction on the stress distribution along the motor axial direction were shown. Also hydrostatic pressurization test was performed to verify finite element analysis in terms of fiber direction strain through the motor case outer surface. Important aspects of analyzing a filament wound pressure vessel were addressed for designers.

Despite the many advances made in material science, stainless steel and aluminum remain the structural materials best-suited for the naval fleet. While these metallic materials offer many benefits, such as high strength and good toughness, their persistent exposure to the maritime environment inevitably leads to issues with corrosion. Among the various manifestations of corrosion, pitting corrosion is of particular concern because the transition of corrosion pits to stress-corrosion cracks can lead to catastrophic failures. Traditional pitting corrosion analyses treat the pit shape as a semi-circle or ellipse and typically assume a growth pattern that maintains the original geometrical shape. However, when the underlying microstructure is incorporated into the model, pit growth is related to the grains surrounding the pit perimeter and the growth rate is proportional to crystallographic orientation. Since each grain has a potentially different orientation, pit growth happens at non-uniform rates leading to irregular geometries, i.e., non-circular and non-elliptical. These irregular pit geometries can further lead to higher stresses. This work presents a detailed look at corrosion pit growth coupled with mechanical load through a numerical model of a two-dimensional stable corrosion pit. Real microstructural information from a sample of 316 stainless steel is incorporated into the model to analyze microstructural effects on pit growth. Through this work, stress distributions and stress concentration factors are examined for a variety of pit geometries, including comparisons of their range of values to a typical, semi-circular pit. The consequences of these stress distributions and concentration factors are discussed.

The complicated steel wheel and rail interaction on curve causes side wear on rail head. Thus, the cost of maintenance for the track on curve is significantly higher than that for track on a tangent. The objective of this research is to develop 3D printing technology for repairing the side wear. In this paper, the study examines induced residual thermal stresses on a rail during the cooling down process after 3D printing procedure using the coupled finite volume and finite element method for thermal and mechanical analysis respectively. The interface of the railhead and additive materials should conserve high stresses to prevent any crack initiation. Otherwise, the additive layer would likely shear off the rail due to crack propagation at the rail/additive interface. In the numerical analysis, a cut of 75-lb ASCE (American Society of Civil Engineers) worn rail is used as a specimen, for which a three-dimensional model is developed. The applied residual stresses, as a result of temperature gradient and thermal expansion coefficient mismatch between additive and rail materials, are investigated. At the beginning, the worn rail is at room temperature while the additive part is at a high initial temperature. Then, additive materials start to flow thermal energy into the worn rail and the ambient. The thermal distribution results from thermal analysis are then employed as thermal loads in the mechanical analysis to determine the von-Mises stress distribution as the decisive component. Then, the effect of preheating on residual stress distribution is studied. In this way, the thermo-mechanical analysis is repeated with an increase in railhead’s initial temperature. In thermal analysis, the temperature contours at different time steps for both the non-preheated and preheated cases indicate that preheating presents remarkably lower temperature gradient between rail and additive part and also represents a more gradual cooling down process to allow enough time for thermal expansion mismatch alignment. In mechanical analysis, the transversal von-Mises stress distribution at rail/additive interface is developed for all cases for comparison purposes. It is shown that preheating is a key factor to significantly reduce residual stresses by about 40% at all points along transversal direction of interface.

Given the current trend in manufacturing to decrease part variability, and in order to increase product quality, dimensional tolerances are becoming more exacting. With this in mind, and with the decreased time allotted for components to progress from design to manufacture, it has become more critical that accurate models of the manufacturing process are developed. This paper investigates the changes in cross sectional area when a prismatic bar is plastically deformed into a ring of constant diameter. Through further processing, these rings are transformed into components that function to secure mechanical components, such as bearings, into assemblies. Failure of the ring can cause significant damage, or failure of the assembly. Typical thickness tolerances are on the order of +/−.002” (0.05 mm), but can be as small as +/−.0002” (0.005 mm). Also, a growing trend in manufacturing is for the final ring to have a specified thickness on the inner and outer edge within this tolerance band. The rings are produced in various metallic materials with different mechanical properties by continuously coiling prismatic bars to a specific diameter. An analytic model based on small strain theory was developed for the simple cross sections of rectangular and trapezoidal geometries. This model was then extended to include the effect of a hyperbolic rather than linear stress distribution through this simple section in order to relieve the constraints of small strain theory and adequately model the actual process. An empirical model was developed based on experimental observations. A numerical model was developed using the commercial finite element analysis (FEA) software Abaqus (SIMULIA, Providence, RI) to simulate the manufacturing process. This was compared to the empirical model developed from production parts for validation. Once the finite element model is validated, it could be used to explore the effects of design parameters (initial dimensions of the prismatic bar, material properties etc.) and create efficient designs for manufacturing. The empirical model can then be used in the design process. Additionally, the numerical simulation could be used to model more complex cross sectional areas which cannot be evaluated analytically. There was adequate agreement between the empirical and numerical models to the extent that the numerical model could be used for more complex cross sectional geometries. A further refinement of the analytic model to include finite strain theory should be used to expand on this.

Pipes carrying heated-pressurized fluid have numerous manufacturing defects that resulted from thermal loadings. Therefore, study the thermal loading effect on the cracked pipes is important to decrease the risks of pipe fracture during their operation. In this work, the effect of the thermal stress distribution on the cracked pipes has been studied numerically. The “mode I” type of crack has been considered for the study. The results have been validated with an available analytical solution for a pristine cylinder. The temperature and stress distribution for different crack length ratio has been studied. The influence of surface’s temperature and fluid’s temperature on radial stress, tangential stresses are discussed. The J-integral and stress intensity factor in analyzed for various thermal conditions. In addition, the radial and tangential stress variations of the various pressurized fluids which have various temperature have been investigated. The stress intensity factor and the J-integrals were calculated for different crack length ratios. In addition, the effect of surface temperature has been studied. It was found that the surface and fluid’s temperature affects the stress distributions and J-integral values. The results show that the J-integral and the stress intensity factor increases as the surface temperature of the pipe increases while their values decrease with increase the surface temperature.

A tree may be the earliest multifunctional structure, and wood is the oldest known engineering material. Yet, trees have no place in engineering education. If we view a tree from merely a mechanical or civil engineering perspective, engineering mechanics can be learned from the tree’s example. Trees have survived by adapting to the most difficult circumstances: heavy winds, rains, floods, droughts, earthquakes, mammal damage, human intervention, etc. The root system must be strong and flexible enough to support the tree’s entire structure from varying load conditions and to provide food storage and nutrient transfer. The stem system provides structural support for the tree’s above-the-ground parts and transfers water and nutrients from the roots through the network of thick-walled cells to other parts of the tree. Leaves produce food and form the surface area surrounding the tree. Leaves come in a variety of shapes and sizes. The tree’s crown, comprising branches, leaves, and reproductive elements, help the tree to catch more sunlight. It moves upward and outward to expose more of its leaves to direct sunlight for photosynthesis while maintaining physical balance on the earth. A tree’s lifecycle can span hundreds of years, despite its vulnerability to constantly changing loads throughout the day and throughout its life. In monsoon and windy seasons, trees endure extremely difficult fatigue-loading. Various parts of the tree and its stem are subjected to combined loading conditions: tension, compression, shear, bending, and torsion. Trees develop and adapt stress management strategies by adjusting their shapes to the type or level of stress they endure: they add more mass where more strength is needed, allows material to easily break off (or physiologically inactive) from locations where it is not necessary, design optimum shapes, and create variable notch radii for reducing stress concentration. But a tree is much more than a structural member. It provides food and shelter for wildlife. It absorbs atmospheric carbon dioxide and produces oxygen. It lowers air temperature and facilitates the water cycle. Structural analysis of a tree can benefit engineering students and practicing engineers alike. Furthermore, a deeper understanding of trees can help us to create multifunctional designs that are in a symbiotic relationship with other members in the system. In short, studying tree mechanics can help us to become better engineers. This paper presents our efforts to integrate trees into engineering curricula to teach mechanics ranging from equilibrium study to stress analysis. Students of statics, dynamics, the strength of materials, stress analysis, material science, design, etc., can benefit from learning about trees. This approach enables students to understand the complexities of real-world living systems, appreciate the genius of nature’s design, and develop methods for creating sustainable designs.

In designing a bolted joint consisting of dissimilar hollow cylinders, the load factor (the ratio of an increment in axial bolt force to an external tensile load) is important. In the present paper, the effect of the load application point, the ratio b/a of the outside diameter to the inside diameter of dissimilar hollow cylinders, Young’s modulus ratio between the dissimilar hollow cylinders on the load factor and the interface stress distribution are examined using FEM calculations. As a result, it is found that the values of the load factor decrease as the ratio b/a increases and the positions where the load application point approaches the interfaces while the value of the load factor is independent of the bolt preload. In addition, it is found that the value of the load factor is less than 0.1 for steel and steel hollow cylinder joints, it is less than 0.2 for aluminum and aluminum hollow cylinder joints and it is less than 0.15 for aluminum and steel hollow cylinder joints while the material of bolt is steel in the present study. For verification of the FEM calculations, experiments to measure the load factor and a load when the interfaces start to separate were carried out. The FEM results are in a fairly good agreement with the experimental results. Finally, based on the obtained results, a design method for bolted joints with dissimilar hollow cylinders is demonstrated for determining the nominal bolt diameter and the bolt strength grade.

The objective of the paper is to examine bolt loosening behavior in a bolted joint under transverse loading both experimentally and numerically. Bolt loosening tests were carried out using Junker’s type loosening machine. In the Junker’s loosening tests, repeated transverse displacements (displacement range S = ±0.35mm were applied to a bolted joint with a M10 hexagon bolt and nut, and then a reduction in the axial bolt force was measured. In the FEM calculations, bolt loosening behavior was examined for a model of Junker’s type loosening machine. In addition, the effects of the flatness and the surface roughness at the bearing surfaces in a clamped part on the reduction in the axial bolt force were examined in the FEM calculations. As a results, it was found that the nut rotation occurred when a glider plate moved toward to the center of the joint from the right and the left dead points. In addition, bolt loosening mechanism was elucidated using the change in the contact stress distribution at the engaged screw threads. The reduction in axial bolt force was found to be the largest for the first 1 cycle loading and then it decreased gradually as the loading cycles increased. An amount of the reduction in the axial bolt force was predicted in the FEM calculation taking account of the flatness (inclined of clamped part) and the surface roughness (contact surface ratio) in 10 loading cycles. The contact surface ratio (surface roughness) was found to significantly affect the reduction in axial bolt force. The predicted results were in a fairly good agreement with the experimental results. Furthermore, the effects of the grip length and the nominal bolt diameter were examined on the bolt loosening behavior experimentally.

Assembly Fiber-Reinforced Thermoplastic Polymer (AFRTP) is a hybrid material manufactured by injection overmolding of short/long fiber-reinforced thermoplastic resin on the back of continuous fiber-reinforced laminate preformed by thermal stamping to achieve both high mechanical properties and complex geometries. This new technique has attracted large attention from industry recently. The difficulty in applying AFRTP is the progressive damage prediction of heterogeneous interface because the difference in mechanical properties result from materials and process may lead to the interface separation when subjected to bending or tension loads that reduce the bending resistance capability of AFRTP plates. In this paper, the interfacial cohesive parameters of AFRTP structure are identified based on the published experimental data. Additionally, the low-speed impact under three-point bending loads is simulated and the interface stress distribution and failure modes reveal the damage mechanisms of AFRTP interface under shear stress.

Adhesive joint technology has been developed gradually, and the application fields of this type of joints have been expanded increasingly since they reduce the weight of the applications, provide uniform stress distribution across the joints, allow to bond similar, and dissimilar materials, and contribute to dampen the shock, and vibration. However, the performance of the adhesive joints under high loading rate such as blast or ballistic loading has been studied by few researchers. In this study, fully laminated plates consisting of 6061 aluminum plates (15” in diameter and 1/16” thick) and FM300K epoxy film adhesive were tested under shock wave loading. Full displacement field over the testing plates were obtained by TRC-SDIC technique, and the strain on the plates were computed by classical plate theory for large deflections. FEM model was analyzed and the results were compared with experimental results.

Fiber-matrix debonding is a common type of failure in composite materials. A computational model that illustrates this damage-induced separation between glass fiber and epoxy matrix in a fiberglass composite model is created from the ground-up. Material properties for the simulations are determined via in-house performed experiments. The tensile modulus of the epoxy matrix is determined to be 8.21 GPa measured using resin-only specimens according to ASTM D638-14. The glass fiber is a bundle of glass fibers extracted from a lattice-woven tape with the original purpose of fiberglass crack patching. These bundles contain approximately 1000 individual fibers per roving. A field-emissive scanning electron microscope study of the glass fiber reveals that the individual fiber diameters vary from 11.04μm to 13.52μm with an average of 11.97μm and a standard deviation of 0.604μm. Tensile tests are performed to the glass fiber bundles using custom grips designed in accordance to ASTM D7269. From these tests, it is found that the fiber Young’s Modulus ranged from 42 GPa to 61.7 GPa. Furthermore, in order to simulate a physical analogue to our computational simulations cylindrical composite specimens of a single bundle of fibers running through the central axis of the cylinder with 6.35mm diameter and 100mm length were prepared and tested. It is found that all of the test specimens exhibit some amount of debonding post-failure. The computational simulation is created in ABAQUS 6.14 to replicate the effects of the experimental composite and elucidate the debonding behavior on smaller time scales. The lower outer face is given a static pinned boundary condition while the upper outer face is given a displacement boundary condition to simulate the fixed lower grips and moving upper grips during the tensile test. The material properties obtained by the experimental tests are applied to the materials in the simulation. Two separate damage models are used in order to simulate breakage; the fiber and matrix utilize the Johnson-Cook failure model as plastic strain-to-failure and the fiber-matrix interface is governed by cohesive-zone elements. The computational model exhibits realistic stress distribution as well as calculates element deletion to simulate interfacial debonding. The simulations are able to show the matrix cracking at the notch and subsequently a separation between the fiber-matrix interface similar to the physical composite analogue.

Recently, the observation technology of micro structure has made great progress, and then collagen fiber orientation of meniscus can be measured accurately. This makes it possible to evaluate the stress in knee joint by considering the collagen fiber orientations at the micro scale. In this study, we developed visco-isotropic/anisotropic hyperelastic constitutive equations (Iso-VHE/Aniso-VHE) for menisci, which can reflect the initial collagen fiber orientations and their deformation induced rotations. Subsequently, we constructed a finite element (FE) model of normal human knee joint by using the magnetic resonance (MR) tomography images. The FE analysis with the proposed constitutive equations and FE model clarifies the reinforcement effect of collagen fibers on mechanical characteristics of knee joint. Our computational prediction clarified that the stress concentration occurred on the contact parts of articular cartilages of femur and tibia, which met the tendency of the experimental results. Furthermore, the maximum compressive stresses evaluated by Aniso-VHE always showed a lower value as compared with Iso-VHE. This suggested that the anisotropy of meniscal collagen fibers relieved the stress concentration and lowered the maximum value. Therefore, our proposed FE analysis was proved to have a potential to reveal the functions of meniscus and knee joint.

A proximal femur fracture due to osteoporosis is one of serious health care problems in aging societies. Osteosynthesis with pin or screw type of implants, such as Hansson pin (HP), Dual SC Screw (DSCS), is widely used for femoral neck fracture treatment in Japan. Unfortunately, some complications such as secondary fractures, especially peri-prosthetic fractures, may occur during postoperative rehabilitation period. In order to reveal the potential cause of the postoperative fracture from the viewpoint of the biomechanics, authors had already performed the dynamic stress analysis of the treated proximal femur based on finite element (FE) analysis. The final goal of our project is to establish the reliable postoperative bone fracture risk assessment method in response to the daily activity including mainly walking. The aim of this study is to propose a novel elastic multi body analysis method based on FE analysis for proximal femur biomechanics. Patient-specific 3D left hip joint FE model was constructed from an elderly female volunteer’s CT images. The model consists of the pelvis, proximal femur, cartilage and DSCS, as multi bodies. The dynamic loading and boundary conditions were applied to the model for simulating a gait motion. Direction and magnitude of the loads varies in response to the gait motion. The time dependent loading forces; hip contact, gluteus medius, gluteus maximus, tensor fasciae latae and adductor, acting around the hip joint was obtained by inverse dynamic analysis of a human gait using in-house lower-limb musculoskeletal model. These loading and boundary conditions for simulating the gait motion are the major technical advantages of the proposed multi body analysis comparing with the conventional static FE analysis. Time varying stress distribution during the gait was evaluated by using dynamic explicit method via ABAQUS. In order to visually demonstrate dynamic stress distribution, we examined the time varying von Mises stresses at the representative points located on the cortical surface of the proximal femur; femoral head, fracture surface and around the lateral insertion holes. The results indicate significant increase of the stresses around the proximal lateral insertion holes for DSCS treatment. Maximum stress values are good agreement with the previous static FE analysis, on the other hand, these biomechanical discussions based on the stress time histories are only obtained from the proposed method. It is indicated that the proposed method is feasible to support the better pre- and postoperative clinical decisions, which is the main contribution of this study.

This work emphasizes on the geometric and dimensional accuracy of cylindrical tailor welded blank (TWB) components manufactured under warm forming conditions. In this work, TWB sheet material made of austenitic stainless steel (ASS 304 Grade) and deep drawing steel (IS 513 grade) materials were TIG welded before subjecting to stamping operation. Numerical simulations were validated with experimental results. Simulation results were analyzed to check the thickness variation and stress distribution within the component which otherwise would be difficult to measure experimentally. Measurements in terms of geometric accuracy gave encouraging results. The roundness and perpendicularity measurements indicated better accuracy whereas, cylindricity value has slightly improved. However, dimensional accuracy of the parts in terms of thinning, cup height and diameter has deteriorated. It was found that the spring back effect played a significant role in the deterioration of dimensional accuracy. Presence of residual stresses might be the cause for this effect; further studies are needed to address this issue.

Adhesive bonding of composite structures has been widely applied in aviation, aerospace, automotive and other industry fields due to the advantages of no holes required, no stress concentration, relative light weight, corrosion resistance and capability of connecting dissimilar materials. However, the strength of joining is greatly influenced by the properties of adhesives and surface treatment of adherents, the geometry and dimension of joints, loading and environmental factors, as well as the curing process and so on. When the finite element (FE) method is used to investigate the influence of above factors on structural response and to optimize the joining design, parametric modeling is required to avoid huge repetitive preprocess work at each evaluation. In this paper, the three-dimensional parametric FE models of Single Lap Joint (SLJ) between carbon fiber-reinforced polymer (CFRP) and steel was established and updated based on the published test data. Using the verified parametric model, the influence of adhesive layer thickness and relative stiffness on the joining strength is investigated, and the results provide a theoretical basis for the design of adhesion joints between CFRP and steel.

In three-dimensional packaging module which have been used in electronic equipment, the size of partial interconnections and total structure have been continuously miniaturized for improving the performance of the products. Due to the fluctuation of the mechanical properties of the component materials and the drop impact towards the fragile modules during manufacturing and operation, the final residual stress varies easily in a chip of the 3-D structure. Both the static and dynamic changes of the stress distribution induce the variation of the performance of electronic devices and the degradation of their long-term reliability. It is, therefore, important to control and optimize the residual stress quantitatively. In this study, a stress sensor which can monitor the change of the local residual stress in 3-D module was developed by applying the piezoresistance effect of single-crystalline silicon. The sensor was embedded in a silicon chip, and it can measure the periodic stress in a silicon chip assembled by area-arrayed bump structure. The impact stress during the manufacturing process was successfully monitored by using this sensor. It was also confirmed that the effective amplitude of the impact stress varies drastically depending on the mechanical properties of the stacked thin films.