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Paper pulper machines a capacity of 83 litres/process must have a low-cost material, robust and safe to operate. Paper pulper machine components analysed are tubes, frames, helical screw shaft and the shaft holder. The method uses a static structural analysis to obtain von mises stress and displacement. Static structural analysis uses finite element analysis with the help of CATIA® Software. The safe component size and lowest cost (safety factor more than 2.5) were selected in this study. Calculation of costs by multiplying the size of the material needs by material prices. Tube components use SUS 304 with thickness variations of 0.5, 0.6, 0.8, 1, 1.5, and 2mm. Frame and shaft holder using L shape ASTM A36 size 40x40mm and 50 x50 mm with thickness variations of 3, 4, and 5 mm respectively. Variations in material size are determined based on standard material sizes available on the market. The simulation result of each component shows the thicker the material, the lower the von mises stress, the lower the displacement and the higher safety factor. Tubes with a thickness of 0.5mm have a von mises stress of 4.43 MPa, a displacement of 4.7 x 104 mm with SF 56.4 is safe and were chosen because of the lowest material costs (IDR 360,009). The frame size was chosen 40x40x3 mm based on the SF frame value (26) with the lowest material cost (IDR 197,800). The shaft holder is also chosen for the size of 40x40x3mm where the SF value (3834) and the lowest material cost (IDR 14,400). Helical screw shaft size is chosen at 0.5mm thickness where SF is 304 and material costs IDR 100,968. The overall results of the static structural analysis on various sizes of the paper pulper machine components showed ovon under Oyield, small displacement, and SF is safe.

This paper presents an experimental work investigating the failure data of oil-impregnated paper under pulsating DC voltage. The failure data of the oil-impregnated paper specimens were obtained through constant voltage stress tests; the Weibull distribution was used to estimate the statistical distribution of failure data. The exponential function (EF) and the inverse power function (IPF) were used to modify the Weibull distribution of failure data, so as to obtain two dual-variable Weibull failure distributions (WFDs), which were used to analyze failure data of oil-paper specimens obtained under pulsating DC and individual DC and AC voltages. Their adequacies were evaluated by using failure data obtained through the constant stress tests under various voltages. Both EF-modified and IPF-modified WFDs show more adequacy for failure data of oil-paper insulation under DC and pulsating DC voltages than AC voltages. The EF-modified WFD was more adequate than IPF-modified WFD in estimating the statistical distribution of failure data.

The early studies on mechanical model of paper honeycomb structures were always concentrated on static situation, however, paper honeycomb would meet some random events of impacting and vibration during the process of transportation. Considering the virtual working circumstance, dynamic experiments under medium and low strain rates were undertaken and corresponding models of mechanical properties were derived. There exists a certain strain-rate effect which leads to the difference of mechanical properties between dynamic and static condition. A mechanical model was given to estimate plateau stress and yield stress at different strain rates based on experimental data by employing the methods of Cowper–Symonds model and piecewise function. The conclusion can be applied to characterise and improve the compressive properties of paper honeycomb structure efficiency.

The mechanical properties of paper honeycomb will be different from static situation with the changing of strain rate, which has an influence on the application of paper honeycomb. In this paper, the dynamic mechanical properties of paper honeycomb were discussed and the corresponding mathematic model was built in order to present the stress in different deformation stages and depict the energy absorption properties of honeycomb structure. The strain-rate effect was expressed by Comper-Symonds model. According to the mechanical model, the energy absorption diagram under different strain rates was also built from selecting materials of cushion packaging and optimum design of the packaging. Finally, serious experiments were taken and the result showed a good agreement with theoretical models. The proposed model can be used for practical application of the optimum design and material selection of honeycomb sandwich structure.

This paper presents analysis of a 3-dimensional engineered structural panel (3DESP) having a tri-axial core structure made from phenolic impregnated laminated-paper composites with and without high-strength composite carbon-fiber fabric laminated to the outside of both faces. Both I-beam equations and finite element method were used to analyze four-point bending of the panels. Comparisons were made with experimental panels. In this study, four experimental panels were fabricated and analyzed to determine the influence of the carbon-fiber on bending performance. The materials properties for finite element analyses (FEA) and I-beam equations were obtained from either the manufacturer or in-house material tensile tests. The results of the FEA and I-beam equations were used to compare with the experimental 3DESP four-point bending tests. The maximum load, face stresses, shear stresses, and apparent modulus of elasticity were determined. For the I-beam equations, failure was based on maximum stress values. For FEA, the Tsai-Wu strength failure criterion was used to determine structural materials failure. The I-beam equations underestimated the performance of the experimental panels. The FEA-estimated load values were generally higher than the experimental panels exhibiting slightly higher panel properties and load capacity. The addition of carbon-fiber fabric to the face of the panels influenced the failure mechanism from face buckling to panel shear at the face–rib interface. FEA provided the best comparison with the experimental bending results for 3DESP.

In this work the crack initiation stress of notched specimens of filter paper is studied. The paper in the microstructure has a random array in their fibers while macroscopically it behaves anisotropically. The self-affine crack mechanics is used to study the size effect in the tensile behavior of this kind of paper under the presence of several conditions of geometrical notches. While in the traditional fracture mechanics the crack initiation stress is a material parameter when is reached a critical level at the crack tip, in the self-affine crack mechanics, depends moreover of the resulting tortuosity of the crack. Four geometrical arrangements in two sizes we considered: centered circular notch, centered lineal notch, sided circular notches and without notch at 10 and 300 mm width with a relation 2a/w = 0.25 under the same loading conditions. In this, the without notch specimens present the higher stress, all other notched specimens presented a similar crack initiation stress about 1 % of difference among them, and the crack growth is not affected by the geometry of notch. In spite of this difference, no one of the specimens reach the theoretical stress concentration of 3 such as predicted the classical stress theory.

The force analysis on the in-plane and out-of-plane of honeycomb core referring to some related articles is presented. during the transportation of wine, the honeycomb paper core is under three-dimensional stress. According to stress condition in the process of wine packaging and transportation, based on the fourth strength principle, the equivalent load is obtained. And the stress with different stretching angels with virtual sampling method is calculated. Thus, the optimal stretching angle of honeycomb paper is acquired, which is .

Cellulosic webs, such as paper materials, are composed of an interwoven, bonded network of cellulose fibers. Strength-controlling parameters in these webs are influenced by constituent fibers and method of processing and manufacture. Instead of estimating the effect on tensile strength of each processing/manufacturing variable, this study modifies and compares the point stress criteria and average stress criteria models used to estimate defect-free (i.e., maximum possible) tensile strength and the inherent size of the cumulative effect of strength-limiting defects. The two major modifications to these models were to assume that defect-free tensile strength was unknown and that unnotched tensile strength was reduced by the presence of inherent defects. These modifications allow the calculation of inherent defect size and defect-free tensile strength by characterizing the tensile strength of the web in the presence of stress concentrations associated with holes of different radius. The models were applied to seven paper materials including lightweight, commercial papers, linerboards, and cylinder boards; estimated inherent defect sizes ranged from 0.1 to 1.5 mm. For most materials considered, defect size was larger in the 2-direction than the 1-direction. Actual measured tensile strengths ranged from 59% to over 95% of the estimated defect-free tensile strengths, σu.

The relationship between the behavior of paper during converting operations and the mechanical properties of paper are a fundamental issue for both paper producers and converters. In the attempt to establish these relationships and thus be able to judge the performance of paper, several testing methods have been developed. The major obstacle to achieve this goal is the fact that the stress conditions acting on paper are not always clearly defined neither in converting operations nor during testing. The first step to achieve a better understanding of the problem is to determine the fundamental mechanical properties of paper.Secondly, the stress condition occurring during converting must be investigated. In this respect, the modeling of paperboard represents a fundamental tool, allowing for the definition of the stress acting on paper during virtually every stage of the converting process or testing. These two steps lead to a better choice of the testing methods that are more relevant for each specific converting operation. The studies presented in this thesis investigate the different aspect of out of plane resistance in paper materials, with particular attention to the problem of delamination during offset printing.

In this work the self-affine crack pattern in Filter Paper sheets is studied. This paper has a well-defined anisotropy of mechanical properties associated with visible preferable orientation of fibers in the machine direction. Fracture behavior is in essence brittle, the rupture lines have self-affine invariance, and the stresses ahead of the straight notch follow a power-law behavior. The roughness exponent value is of H = 0.50 0.01, different from the suggested universal value H = 0.8. The classical theory has demonstrated that, in materials such as metal, there is a relationship between the size and the starting crack stress, which does not happen in this material. The tests show that the starting crack stress from stress-strain behavior curves remains stable for the different specimen sizes w and crack length size. Moreover, different types of geometric groove, circular and linear, and without a crack, were tested and show almost the same behavior.

Recycled paper is helpful to reduce trash discharge, save resource and cost. Tube is one of the most common structures of recycled paper in application. It is an excellent choice for packing. It’s also used in the construction of temporary structures for both exhibition spaces or for rapid-recovery shelters in emergency operations. As paper tubes are laminated by paperboards which are inherent anisotropy materials, the researches on mechanical property and fracture behavior became complicated. In the current study, paperboards used for paper tubes were tested on universal testing machine to investigate their basis mechanical properties. Then, paper tubes fabricated with different kinds of paperboard and number of ply were used to investigate lateral compressive properties by Instron universal testing machine. And, a camera was employed to record the fracture process of paper tube during compression process. The fracture mechanism of paper tubes were discussed and analyzed during compressed process based on the load-displacement curves and detailed observation. Additionally, ls-dyna software was used to conduct numerical simulation and analyze stress distribution of paper tube during lateral compression.Copyright © 2014 by ASME

A classic hygro-viscoelastic constitutive model applicable for the analysis of time and humidity-dependent stresses of paper structures using the finite element method (FEM) was investigated. For t ...

This paper describes theoretical and experimental studies of the velocity characteristics of a paper transport mechanism that consists of a short rubber-layered roller and a steel roller. The deformation and strain of surface of the driving rubber roller are numerically calculated based on Boundary Element Method by using Green's function that has been derived in the polar coordinates under the in-plane stress assumption. The effects of the normal load F and the paper tension T on the strain of the rubber roller are calculated. The velocity ratio of the paper transport velocity to the tangential velocity of the rubber roller is derived from the strain of the rubber roller. In order to verify the numerical results, an experimental setup of a friction drive mechanism for an endless paper was prepared. The paper transport velocity and the tangential velocity of the rubber roller were measured by changing the operating conditions. It was shown that the theoretical result can predict precisely the effect of the normal load F, the paper tension T and the rubber thickness on the velocity ratio in the range of-0.1?T/F?0.2 when 69°Hs rubber roller is used.

Electrical failure of insulation is known to be an extremal random process wherein nominally identical pro-rated specimens of equipment insulation, at constant stress fail at inordinately different times even under laboratory test conditions. In order to be able to estimate the life of power equipment, it is necessary to run long duration ageing experiments under accelerated stresses, to acquire and analyze insulation specific failure data. In the present work, Resin Impregnated Paper (RIP) a relatively new insulation system of choice used in transformer bushings, is taken as an example. The failure data has been processed using proven statistical methods, both graphical and analytical. The physical model governing insulation failure at constant accelerated stress has been assumed to be based on temperature dependent inverse power law model.

According to the quasi-static compression experiment and the creep experiment results, the paper honeycomb panel can be modeled as linear material with viscoelastic property whose relaxation kernel is expressed by a sum of exponentials. A parameter identification procedure is formulated which is based on the Prony method and the free response data of the single degree of freedom system. The stiffness coefficient, damping coefficient and the viscoelastic parameters under different static stress can be obtained using the free vibration response data of the honeycomb-mass system through the procedure. The parameters obtained here provide some basic data for the proper use of paper honeycomb panel in protective packaging design.

At present it is the consensus that structures should be desitned to undergo ductile deformations if subjected to very strong ground shaking, so structures designed without consideration of large deformations can be expected to experience undesirable damage. However, in most strong earthquakes some unexpected ground motion or unexpected structural failure occurs which deserves closer examination. In both the Northridge and the Kobe earthquakes there were unexpected ground motions as well as unexpected structural damage. The reason such failures are unexpected is that their possibility was not identified during the design process.

A simple design procedure, based on 114 finite element analyses, was derived to predict the stress intensification factor for 90-deg curved pipe with end constraints composed of tangents of any length terminated by rigid flanges and no internal pressure loads. The results of this design procedure were then compared to stress intensification factors obtained from additional finite element analyses and experimental work. Stress intensification factors calculated using the design equations in the Power Piping Code (ANSI/ASME B31.1-1986) were also compared to all the finite element and experimental work. It was found that this design procedure more accurately predicts the stress intensification factors than the Power Piping Code.

The four-point bend test is used extensively to measure the edge (and surface) strength of AMLCD displays both in panel form and single substrate. The subtleties of four-point bend test for AMLCD panel applications and how one might use additional techniques, such as strain gage, finite element modeling and failure mode analysis, to better understand the data generated are investigated. This paper attempts to show the following: i) the standard four-point bend equation (figure 1) is not applicable to thin AMLCD panels, ii) the edges and surface experience different stress, iii) stresses can be quantified by knowing break location and the appropriate strain level, and iv) failure mode analysis can support the strain analysis and provide valuable information to the experimenter.

It is shown, in the light of three very different case studies, that a narrow belt stiffening when suitably attached at the geometric discontinuity of a joint existing on a vessel, tank or pipe intersection, is able to produce a remarkable reduction in the stress concentration. This is reason to believe that the narrow belt stiffening, when dimensioned correctly and attached properly, may be used extensively to reduce stress gradients in joints existing on vessels, tanks, pipings and related structures. Understandably, a narrow belt stiffening should be used with great caution for junctions that do not operate at ambient temperature, being unsuitable for applications involving substantial thermal stresses.

It has been reported that the insulation design under DC stress is considered as one of the critical factors in determining the performance of high-voltage direct current (HVDC) superconducting cable. Therefore, it is fundamentally necessary to investigate the DC breakdown characteristics of the composite insulation system consisting of liquid nitrogen (LN2)/polypropylene-laminated-paper (PPLP). In particular, the insulation characteristics under DC polarity reversal condition should be verified to understand the polarity effect of the DC voltage considering the unexpected incidents taking place at line-commutated-converters (LCC) under service at a DC power grid. In this study, to examine the variation of DC electric field strength, the step voltage and polarity reversal breakdown tests are performed under DC stress. Also, we investigate the electric field distributions in a butt gap of the LN2/PPLP condition considering the DC polarity reversal by using simulation software.

The compressive behaviour of paper honeycombs is studied by means of an experimental analysis. Experiment results show how geometry aspects of hexagonal paper honeycombs,e.g. the height of paper honeycomb,the thickness and length of honeycomb cell-wall,the drawing ratio of hexagonal honeycomb,affect the compressive properties of the paper honeycombs. It is in good agreement with the theory model. The constraint factor K of the critical buckling stress is mainly determined by the length of honeycomb cell-wall. It can be described as K=1.54 for B type paper honeycombs and K=3.32 for D type paper honeycombs. The plateau stress is the power exponent function of the thickness to length ratio of honeycomb cell-wall,and the experiment results show that the constant is 13.2 and the power exponent is 1.77. The research results can be used to characterize and improve efficiently the compressive properties of paper honeycombs.

A brief survey of plastic buckling of axially compressed cylindrical shells is given. Results of nonlinear finite element analyses of several axially compressed, ring-stiffened, steel, cylindrical shells are presented, including comparisons with tests conducted at Chicago Bridge and Iron Co. and at the Los Alamos National Laboratory (LANL). Some of the LANL specimens with radius-to-thickness ratio of about 450 have reinforced circular openings that cut across various numbers of ring stiffeners. These cylindrical shells are loaded by enforced axial displacement applied to thick aluminum end plates halfway between the axis of revolution and the shell wall. Measured imperfections are included in the analysis of one ring-stiffened specimen without any cutout. Inclusion of the imperfection field reduces the predicted collapse load by only eight percent. Reinforced openings that cut one or two or three rings reduce the collapse load by 14, 21 and 22 percent, respectively. Agreement between test and theory for the nonuniformly compressed LANL specimens is within 14 percent, even with initial imperfections neglected in the analysis.

Due to the fact that clamping devices are widely used in various industries, the requirements for the operation of such devices are constantly increasing. This is due to an increase in the general requirements for processing accuracy, as well as an increase in the forces acting on the clamped part. The reliability of these devices when working with thin-walled cylindrical parts is of great importance. Thin-walled cylinders used in mechanical engineering are subject to significant loads. With prolonged exposure to loads from clamping forces, as well as from axial tensile forces, plastic deformations of cylindrical parts occur. In the oil and gas industry, when clamping drill and casing pipes in some areas in the capture zone, stresses exceed the yield strength. Multiple clamping of the pipe will reduce the pipe wall in the gripping area, which causes premature pipe failure. Therefore, increasing the holding capacity of clamping mechanisms is relevant. Analysis of broken drill pipes, which have been operating in wedge grips for a long time, showed that in most cases the pipes undergo plastic deformation caused by damage to the pipe surface by the teeth of the ram. To clarify the actual conditions of loading the pipe and the possibilities of increasing the capacity of the clamping devices, studies of the contact pressures in the clamping zone were carried out. A new pipe clamping chuck is also presented, which provides a sufficiently high reliability of fastening of cylindrical parts.

Sandwich structures with Miura-ori cores have been studied especially in aerospace industry. However, by removing the face sheets one can obtain esthetical, multifunctional, self-supporting structures for various applications, such as packaging. This study focuses on the mechanical performance of planar, self-supporting Miura-ori structures under compressive loads. Through systematic variations of both origami geometry and base material orientation, this study performs linear stress and stability analyses by utilizing the finite element method. The results reveal the effects of the geometric parameters and the material orthotropy on the structural performance, finally resulting in parameter ranges forming a basis for structural design.

Summary Elastostatic and elastodynamic stress singularities play a major part in considerations of fracture mechanics. In this paper some relatively well-known elastostatic results are briefly reviewed. The major part of the paper is, however, concerned with new elastodynamic results for stress intensity factors of a bifurcating crack.

Normal and tangential loads are applied to an elastic half-plane. A crack perpendicular to the surface lies at the edge of the loaded region. The crack behaviour is analysed both theoretically and experimentally. Stress intensity factors are obtained in both cases and compared. In the theoretical work, the Burger vector approach as well as the linearisation techniques first presented by Hills and Comminou are used. However a new algorithm based on the Kalker method developed for unilateral contact analyses yields stress intensity factors. An entire loading and unloading cycle is analysed and presented. Crack interface friction is taken into account. In the experimental work, a thin slit is cut with a razor blade in a birefringent rectangular slab. Stress fields are determined using photoelastic techniques. The isochrome field is diqitized and stress intensity factors are determined. The loading cycle analysed above is tested experimentally. The good agreement noted between theory and experiment validates the theory. This type of information is of particular interest is understanding the relation between surface loading and crack propagation in fretting.

This paper shows the technological development for manufacturing corner angle sections or cardboard. Its manufacture involves splicing sheets (liners) of different weight Kraft papers joined with white glue. The thickness and strength of each profile is determined by the amount of spliced leaves and paperweight. There are two types of finishing in the profile, which are: natural finish Kraft wrapping paper and the white paper envelope. The second one is used to print images or logos on the exterior face for advertising purposes. They can withstand bending stresses for supporting buckling in horizontal and vertical position. These profiles are mainly used for packaging, protect corners, transportation and storage. A machine for manufacturing specialized linear process to obtain the required thickness is used. In this article, the basic load of an angular profile is analyzed by the finite element method using ANSYS 14 ®. Mechanical design considerations based on the mechanics of composite materials and the theory of laminated beams are considered. With the results of this analysis, load capacities like bending, buckling and deformation profiles are obtained. Furthermore, a comparison of three thicknesses of angular profiles supporting the mentioned loads is also presented.

This paper presents a new methodology to localize the deformation range to improve the computational efficiency for soft tissue simulation. This methodology identifies the local deformation range from the stress distribution in soft tissues due to an external force. A stress estimation method is used based on elastic theory to estimate the stress in soft tissues according to a depth from the contact surface. The proposed methodology can be used with both mass-spring and finite element modeling approaches for soft tissue deformation. Experimental results show that the proposed methodology can improve the computational efficiency while maintaining the modeling realism.

This essay analyses the mechanical behavior of the paper machine drying section rack by FEA method, obtaining transformation and stress distribution of the rack under static loading, so as to achieve the natural frequency and the corresponding strain, stress of the rack. This paper could provide theoretical foundation for design, fault diagnosis or reforming speed acceleration.

Two different formulations for the two-surface model of bounded kinematic hardening can be found in literature on shakedown analysis with the von Mises yield criterion. This short paper explains that these two formulations are not equivalent, although there exists literature asserting that they are equivalent. More specifically, the formulation using the constraint on the stress is not a sufficient condition for the two-surface model. Consequently, the static shakedown analysis using this formulation over-evaluates the shakedown factor in general.

Stress peening forming is widely used in the aeronautics industry to induce curvatures in wing skins. Most of the investigations of stress peen forming are empirical and experimental. In this paper, a three step numerical model that can simulate this process was developed. First, an implicit Finite Element Analysis (FEA) with ANSYS where a prebending moment along the spanwise direction of the component was performed. Then, an explicit FEA with LS-DYNA simulating shot impacts on the pre-stressed component was executed in order to obtain the resulting stresses inside the component. Finally, an implicit FEA with ANSYS was performed for calculating the arc heights and the curvature radii of the component in chordwise and spanwise directions. Numerical analysis of the process shows that the prebending moments have an influence not only on the residual stress profiles but also on the curvatures of the deformed component in chordwise and spanwise directions. This model was used to establish a relationship between the prebending moment and the resulting arc heights and residual stress profiles. The numerical strategies developed in this paper supply a useful tool for studying and optimizing the stress peening process. © 2011 Elsevier Ltd. All rights reserved.

In the present study, three layers of the ascending aorta in respect to the time and space at various blood pressures have been simulated. Two well-known commercial finite element (FE) software have used to be able to provide a range of reliable numerical results while independent on the software type. The radial displacement compared with the time as well as the peripheral stress and von Mises stress of the aorta have calculated. The aorta model was validated using the differential quadrature method (DQM) solution and, then, in order to design functionally graded materials (FGMs) with different heterogeneous indexes for the artificial vessel, two different materials have been employed. Fluid–structure interaction (FSI) simulation has been carried out on the FGM and a natural vessel of the human body. The heterogeneous index defines the variation of the length in a function. The blood pressure was considered to be a function of both the time and location. Finally, the response characteristics of functionally graded biomaterials (FGBMs) models with different values of heterogeneous material parameters were determined and compared with the behaviour of a natural vessel. The results showed a very good agreement between the numerical findings of the FGM materials and that of the natural vessel. The findings of the present study may have implications not only to understand the performance of different FGMs in bearing the stress and deformation in comparison with the natural human vessels, but also to provide information for the biomaterials expert to be able to select a suitable material as an implant for the aorta.

This study aimed to experimentally track the tissue-scale strains of the tendon–bone attachment with and without a localized defect. We hypothesized that attachments with a localized defect would develop strain concentrations and would be weaker than intact attachments. Uniaxial tensile tests and digital image correlation were performed on rat infraspinatus tendon-to-bone attachments with defects (defect group) and without defects (intact group). Biomechanical properties were calculated, and tissue-scale strain distributions were quantified for superior and inferior fibrous and calcified regions. At the macroscale, the defect group exhibited reduced stiffness (31.3±3.7 N/mm), reduced ultimate load (24.7±3.8 N), and reduced area under the curve at ultimate stress (3.7±1.5 J/m2) compared to intact attachments (42.4±4.3 N/mm, 39.3±3.7 N, and 5.6±1.4 J/m2, respectively). Transverse strain increased with increasing axial load in the fibrous region of the defect group but did not change for the intact group. Shear strain of the superior fibrous region was significantly higher in the defect group compared to intact group near yield load. This work experimentally identified that attachments may resist failure by distributing strain across the interface and that strain concentrations develop near attachment defects. By establishing the tissue-scale deformation patterns of the attachment, we gained insight into the micromechanical behavior of this interfacial tissue and bolstered our understanding of the deformation mechanisms associated with its ability to resist failure.

Accurate prediction of failure and forming limits is essential when modelling sheet metal forming processes. Since traditional Forming Limit Curves (FLCs) are not valid for materials subjected to triaxial loading, a new failure criterion is proposed in this paper based on the stress triaxility and the effective plastic strain accumulated during the history of material loading. Formability zones are identified inside the proposed Triaxial Failure Diagram (TFD). FLCs may be mapped into the TFD defining a new Triaxial Failure Curve, or it can be defined by triaxial failure experiments. Several TFD examples are validated and constrasted showing acceptable accuracy in the numerical prediction of forming failure/limit of 3D thick sheet parts.

As abrupt change of the shape and elastic constant in the weld area occurs to the welding joint, there will be obvious stress concentration near the weld area when being loaded. Lifting and Lowering Method and Grouping Method prevailing in the world are applied to conduct an experiment about fatigue strength of a certain welding joint in Wuhan Iron and Steel and S-N curve is drawn in this paper based on the condition of nominal stress. In addition, the influence of weld size of the welding joint on the distribution of stress is studied through the calculation of finite element numeral value and experimental test. According to the factor of stress concentration, S-N curve is modified to provide the data support for the application of the welding joint and assessment of fatigue strength.

There is a need to better understand the effects of intervertebral spacer material and design on the stress distribution in vertebral bodies and endplates to help reduce complications such as subsidence and improve outcomes following lumbar interbody fusion. The main objective of this study was to investigate the effects of spacer material on the stress and strain in the lumbar spine after interbody fusion with posterior instrumentation. A standard spacer was also compared with a custom-fit spacer, which conformed to the vertebral endplates, to determine if a custom fit would reduce stress on the endplates. A finite element (FE) model of the L4–L5 motion segment was developed from computed tomography (CT) images of a cadaveric lumbar spine. An interbody spacer, pedicle screws, and posterior rods were incorporated into the image-based model. The model was loaded in axial compression, and strain and stress were determined in the vertebra, spacer, and rods. Polyetheretherketone (PEEK), titanium, poly(para-phenylene) (PPP), and porous PPP (70% by volume) were used as the spacer material to quantify the effects on stress and strain in the system. Experimental testing of a cadaveric specimen was used to validate the model's results. There were no large differences in stress levels (37%) the stress at the bone–spacer interfaces for all materials tested. A 28% decrease in stress was found in the posterior rods with the custom spacer. Of all the spacer materials tested with the custom spacer design, 70% porous PPP resulted in the lowest stress at the bone–spacer interfaces. The results show the potential for more compliant materials to reduce stress on the vertebral endplates postsurgery. The custom spacer provided a greater contact area between the spacer and bone, which distributed the stress more evenly, highlighting a possible strategy to decrease the risk of subsidence.

The von Mises (VM) stress is a common stress measure for finite element models of tissue mechanics. The VM failure criterion, however, is inherently isotropic, and therefore may yield incorrect results for anisotropic tissues, and the relevance of the VM stress to anisotropic materials is not clear. We explored the application of a well-studied anisotropic failure criterion, the Tsai–Hill (TH) theory, to the mechanically anisotropic porcine aorta. Uniaxial dogbones were cut at different angles and stretched to failure. The tissue was anisotropic, with the circumferential failure stress nearly twice the axial (2.67 ± 0.67 MPa compared to 1.46 ± 0.59 MPa). The VM failure criterion did not capture the anisotropic tissue response, but the TH criterion fit the data well (R2 = 0.986). Shear lap samples were also tested to study the efficacy of each criterion in predicting tissue failure. Two-dimensional failure propagation simulations showed that the VM failure criterion did not capture the failure type, location, or propagation direction nearly as well as the TH criterion. Over the range of loading conditions and tissue geometries studied, we found that problematic results that arise when applying the VM failure criterion to an anisotropic tissue. In contrast, the TH failure criterion, though simplistic and clearly unable to capture all aspects of tissue failure, performed much better. Ultimately, isotropic failure criteria are not appropriate for anisotropic tissues, and the use of the VM stress as a metric of mechanical state should be reconsidered when dealing with anisotropic tissues.

The objective of this study was to develop and validate\ud a subject-specific framework for modelling the human\ud foot. This was achieved by integrating medical image-based\ud finite element modelling, individualised multi-body musculoskeletal\ud modelling and 3D gait measurements. A 3D\ud ankle–foot finite element model comprising all major foot\ud structures was constructed based on MRI of one individual.\ud A multi-body musculoskeletal model and 3D gait measurements\ud for the same subject were used to define loading and\ud boundary conditions. Sensitivity analyses were used to investigate\ud the effects of key modelling parameters on model\ud predictions. Prediction errors of average and peak plantar\ud pressures were below 10% in all ten plantar regions at five\ud key gait events with only one exception (lateral heel, in early\ud stance, error of 14.44%). The sensitivity analyses results suggest\ud that predictions of peak plantar pressures are moderately\ud sensitive to material properties, ground reaction forces and\ud muscle forces, and significantly sensitive to foot orientation.\ud The maximum region-specific percentage change ratios\ud (peak stress percentage change over parameter percentage\ud change) were 1.935–2.258 for ground reaction forces, 1.528–\ud 2.727 for plantar flexor muscles and 4.84–11.37 for foot\ud orientations. This strongly suggests that loading and boundary conditions need to be very carefully defined based on\ud personalised measurement data.

This paper describes a methodology for selecting a set of biomechanical engineering design variables to optimize the performance of an engineered meniscal substitute when implanted in a population of subjects whose characteristics can be specified stochastically. For the meniscal design problem where engineering variables include aspects of meniscal geometry and meniscal material properties, this method shows that meniscal designs having simultaneously large radial modulus and large circumferential modulus provide both low mean peak contact stress and small variability in peak contact stress when used in the specified subject population. The method also shows that the mean peak contact stress is relatively insensitive to meniscal permeability, so the permeability used in the manufacture of a meniscal substitute can be selected on the basis of manufacturing ease or cost. This is a multiple objective problem with the mean peak contact stress over the population of subjects and its variability both desired to be small. The problem is solved by using a predictor of the mean peak contact stress across the tibial plateau that was developed from experimentally measured peak contact stresses from two modalities. The first experimental modality provided computed peak contact stresses using a finite element computational simulator of the dynamic tibial contact stress during axial dynamic loading. A small number of meniscal designs with specified subject environmental inputs were selected to make computational runs and to provide training data for the predictor developed below. The second experimental modality consisted of measured peak contact stress from a set of cadaver knees. The cadaver measurements were used to bias-correct and calibrate the simulator output. Because the finite element simulator is expensive to evaluate, a rapidly computable (calibrated) Kriging predictor was used to explore extensively the contact stresses for a wide range of meniscal engineering inputs and subject variables. The predicted values were used to determine the Pareto optimal set of engineering inputs to minimize peak contact stresses in the targeted population of subjects.

The aim of this study was to determine the biomechanical characteristics of locking plates with the TriLock system with different design and screw settings compared to a non-locking plate in a diaphyseal metacarpal fracture. Oblique diaphyseal shaft fractures in porcine metacarpal bones were created in a biomechanical fracture model. After reduction they were fixed with three different locking plates with the TriLock interlocking mechanism or a non-locking linear plate in mono- or bicortical screw fixations. In load to failure tests the maximum load and stiffness were measured. For linear plates, the maximum load was higher for the non-locking plate compared with the locking plate. The maximum load could be increased for the locking plates using a double-row design and a higher screw number. No differences were found for the stiffness between all groups. In contrast to the non-locking plate, the mode of failure of the locking plates in many cases (86 %) was a loss of the interlocking mechanism. The results suggest that the locking plates with the TriLock system achieve no higher stability compared to a non-locking plate in load to failure tests. Adaptions to increase the stability of the interlocking mechanism are desirable.

Several features of the tendon-to-bone attachment were examined allometrically to determine load transfer mechanisms. The humeral head diameter increased geometrically with animal mass. Area of the attachment site exhibited a near isometric increase with muscle physiological cross section. In contrast, the interfacial roughness as well as the mineral gradient width demonstrated a hypoallometric relationship with physiologic cross-sectional area (PCSA). The isometric increase in attachment area indicates that as muscle forces increase, the attachment area increases accordingly, thus maintaining a constant interfacial stress. Due to the presence of constant stresses at the attachment, the micrometer-scale features may not need to vary with increasing load.

Methods to quantify ventricle material properties noninvasively using in vivo data are of great important in clinical applications. An ultrasound echo-based computational modeling approach was proposed to quantify left ventricle (LV) material properties, curvature, and stress/strain conditions and find differences between normal LV and LV with infarct. Echo image data were acquired from five patients with myocardial infarction (I-Group) and five healthy volunteers as control (H-Group). Finite element models were constructed to obtain ventricle stress and strain conditions. Material stiffening and softening were used to model ventricle active contraction and relaxation. Systolic and diastolic material parameter values were obtained by adjusting the models to match echo volume data. Young's modulus (YM) value was obtained for each material stress–strain curve for easy comparison. LV wall thickness, circumferential and longitudinal curvatures (C- and L-curvature), material parameter values, and stress/strain values were recorded for analysis. Using the mean value of H-Group as the base value, at end-diastole, I-Group mean YM value for the fiber direction stress–strain curve was 54% stiffer than that of H-Group (136.24 kPa versus 88.68 kPa). At end-systole, the mean YM values from the two groups were similar (175.84 kPa versus 200.2 kPa). More interestingly, H-Group end-systole mean YM was 126% higher that its end-diastole value, while I-Group end-systole mean YM was only 29% higher that its end-diastole value. This indicated that H-Group had much greater systole–diastole material stiffness variations. At beginning-of-ejection (BE), LV ejection fraction (LVEF) showed positive correlation with C-curvature, stress, and strain, and negative correlation with LV volume, respectively. At beginning-of-filling (BF), LVEF showed positive correlation with C-curvature and strain, but negative correlation with stress and LV volume, respectively. Using averaged values of two groups at BE, I-Group stress, strain, and wall thickness were 32%, 29%, and 18% lower (thinner), respectively, compared to those of H-Group. L-curvature from I-Group was 61% higher than that from H-Group. Difference in C-curvature between the two groups was not statistically significant. Our results indicated that our modeling approach has the potential to determine in vivo ventricle material properties, which in turn could lead to methods to infer presence of infarct from LV contractibility and material stiffness variations. Quantitative differences in LV volume, curvatures, stress, strain, and wall thickness between the two groups were provided.

The goal of this study is to develop a computational fluid dynamics (CFD) modeling approach to better estimate the blood flow dynamics in the bundles of the hollow fiber membrane based medical devices (i.e., blood oxygenators, artificial lungs, and hemodialyzers). Three representative types of arrays, square, diagonal, and random with the porosity value of 0.55, were studied. In addition, a 3D array with the same porosity was studied. The flow fields between the individual fibers in these arrays at selected Reynolds numbers (Re) were simulated with CFD modeling. Hemolysis is not significant in the fiber bundles but the platelet activation may be essential. For each type of array, the average wall shear stress is linearly proportional to the Re. For the same Re but different arrays, the average wall shear stress also exhibits a linear dependency on the pressure difference across arrays, while Darcy's law prescribes a power-law relationship, therefore, underestimating the shear stress level. For the same Re, the average wall shear stress of the diagonal array is approximately 3.1, 1.8, and 2.0 times larger than that of the square, random, and 3D arrays, respectively. A coefficient C is suggested to correlate the CFD predicted data with the analytical solution, and C is 1.16, 1.51, and 2.05 for the square, random, and diagonal arrays in this paper, respectively. It is worth noting that C is strongly dependent on the array geometrical properties, whereas it is weakly dependent on the flow field. Additionally, the 3D fiber bundle simulation results show that the three-dimensional effect is not negligible. Specifically, velocity and shear stress distribution can vary significantly along the fiber axial direction.

Mechanical forces are important in embryonic development [1] and key factor in the pathogenesis of many diseases including cardiovascular disease [1–3], cancer [4,5], and neurological disorders [6,7]. A variety of devices have been developed to study the effects of mechanical forces on the cells through the application of mechanical strain [8–10]. These systems most commonly involve growing cultured cells on a flexible substrate and applying forces to the substrate with a piston [11–14] or through pneumatic pressure [15–17]. While a key advantage of in vitro systems is the ability to isolate a single cell type and create a well-defined mechanical environment, it is a fundamental limitation of these systems that the movement of the flexible culture substrate generates fluid flow that also applies shear forces to cells in culture. As many cell types are sensitive to fluid shear forces as well as mechanical stretch, the generation of flow may also cause a response from the cells. Thus, it is critical to understand the fluidic forces within these systems to account for this potential confounding factor in these experiments. In particular, endothelial cells have been shown to respond to shear stresses and mechanical strain, leading to modulation of the immune cell interactions [18–20], coagulation factors [21], and vasomotor tone [22,23]. As flow is inevitably generated within the systems that apply mechanical strain, it is unclear what part of the response is induced from the flow or the mechanical stretch. A similar situation is relevant to many cell types including osteoblasts [24,25], vascular smooth muscle cells [26,27], and mesenchymal stem cells [28,29], all of which have shown to have potent mechanobiological responses to mechanical strain in culture and respond strongly to shear forces. There have been only limited attempts to understand the shear forces during the application of mechanical stretch to cultured cells. One previous study used a 2D model of shear stresses in a pneumatically driven system [30] while another used a highly simplified model of flat wall displacement to estimate the order of magnitude of the shear stress generated during the motion of the piston [13]. We recently created a novel device that allows application of complex mechanical stretch waveforms to cultured cells in a six-well format [12]. While we have validated the strain applied by this system in terms of flexible membrane distention, it remains unclear what the nature of the flow is within this system during mechanical loading. Here, we have created a computational simulation of the flow within a culture well with a flexible bottom during the application of mechanical strain. In our model, displacement of the flexible membrane leads to the generation of fluid flow. In the actual system, the pistons are mounted on a rigid plate that is coupled to a linear motor allowing arbitrary displacements and the application of complex temporal strain profiles. In our model, we simulated several common loading profiles including the application of sinusoidal load of 0.5–2.0 Hz and displacements that generate 1–10% maximal strain on the culture membrane. Our results are useful for interpreting the potential effects of shear stress in the many experimental studies that have applied mechanical strain to cultured cells and provide a computational analysis of the flow within these in vitro mechanical loading devices. Moreover, we demonstrate that motion of the membrane within the well leads to the generation of low level oscillatory shear stress that has been shown to alter the function of endothelial cells [19,31,32]. Thus, the analysis presented here may be relevant to many systems in which mechanical forces are applied to cells through displacement of a flexible membrane.

Analytical load–displacement relations for flexure mechanisms, formulated by integrating the individual analytical models of their building-blocks (i.e., flexure elements), help in understanding the constraint characteristics of the whole mechanism. In deriving such analytical relations for flexure mechanisms, energy based approaches generally offer lower mathematical complexity, compared to Newtonian methods, by reducing the number of unknowns—specifically, the internal loads. To facilitate such energy based approaches, a closed-form nonlinear strain energy expression for a generalized bisymmetric spatial beam flexure is presented in this paper. The strain energy, expressed in terms of the end-displacement of the beam, considers geometric nonlinearities for intermediate deformations, enabling the analysis of flexure mechanisms over a finite range of motion. The generalizations include changes in the initial orientation and shape of the beam flexure due to potential misalignment or manufacturing. The effectiveness of this approach is illustrated via the analysis of a multilegged table flexure mechanism. The resulting analytical model is shown to be accurate using nonlinear finite elements analysis, within a load and displacement range of interest.

The bond properties between Reactive Powder Concrete and steel bars is discussed in this paper based on the pullout test results. It is concluded that: the bond stress of deformed bars is larger than round bars, and develops earlier along the whole length. The bond stress-slip relationship between Reactive Powder Concrete and steel bar can simulate with the double line curve model.

Prior multiaxial strength studies on trabecular bone have either not addressed large variations in bone volume fraction and microarchitecture, or have not addressed the full range of multiaxial stress states. Addressing these limitations, we utilized micro-computed tomography (μCT) based nonlinear finite element analysis to investigate the complete 3D multiaxial failure behavior of ten specimens (5 mm cube) of human trabecular bone, taken from three anatomic sites and spanning a wide range of bone volume fraction (0.09–0.36), mechanical anisotropy (range of E3/E1 = 3.0–12.0), and microarchitecture. We found that most of the observed variation in multiaxial strength behavior could be accounted for by normalizing the multiaxial strength by specimen-specific values of uniaxial strength (tension, compression in the longitudinal and transverse directions). Scatter between specimens was reduced further when the normalized multiaxial strength was described in strain space. The resulting multiaxial failure envelope in this normalized-strain space had a rectangular boxlike shape for normal–normal loading and either a rhomboidal boxlike shape or a triangular shape for normal-shear loading, depending on the loading direction. The finite element data were well described by a single quartic yield criterion in the 6D normalized-strain space combined with a piecewise linear yield criterion in two planes for normal-shear loading (mean error ± SD: 4.6 ± 0.8% for the finite element data versus the criterion). This multiaxial yield criterion in normalized-strain space can be used to describe the complete 3D multiaxial failure behavior of human trabecular bone across a wide range of bone volume fraction, mechanical anisotropy, and microarchitecture.

Various techniques exist for quantifying articular contact stress distributions, an important class of measurements in the field of orthopaedic biomechanics. In situations where the need for dynamic recording has been paramount, the approach of preference has involved thin-sheet multiplexed grid-array transducers. To date, these sensors have been used to study contact stresses in the knee, shoulder, ankle, wrist, and spinal facet joints. Until now, however, no such sensor had been available for the human hip joint due to difficulties posed by the deep, bi-curvilinear geometry of the acetabulum. We report here the design and development of a novel sensor capable of measuring dynamic contact stress in human cadaveric hip joints (maximum contact stress of 20 MPa and maximum sampling rate 100 readings/s). Particular emphasis is placed on issues concerning calibration, and on the effect of joint curvature on the sensor's performance. The active pressure-sensing regions of the sensors have the shape of a segment of an annulus with a 150-deg circumferential span, and employ a polar/circumferential “ring-and-spoke” sensel grid layout. There are two sensor sizes, having outside radii of 44 and 48 mm, respectively. The new design was evaluated in human cadaver hip joints using two methods. The stress magnitudes and spatial distribution measured by the sensor were compared to contact stresses measured by pressure sensitive film during static loading conditions that simulated heel strike during walking and stair climbing. Additionally, the forces obtained by spatial integration of the sensor contact stresses were compared to the forces measured by load cells during the static simulations and for loading applied by a dynamic hip simulator. Stress magnitudes and spatial distribution patterns obtained from the sensor versus from pressure sensitive film exhibited good agreement. The joint forces obtained during both static and dynamic loading were within ±10% and ±26%, respectively, of the forces measured by the load cells. These results provide confidence in the measurements obtained by the sensor. The new sensor's real-time output and dynamic measurement capabilities hold significant advantages over static measurements from pressure sensitive film.