Approach For Stress Analysis Research Articles

A post-processor approach for stress analysis of woven textile composites

In this study, macro-elements have been extended for the post-processing of detailed stresses of woven-textile composites. A symmetric plain-weave unit-cell configuration was analyzed to evaluate the performance of the post-processors. The stress results by macro-element post-processors were compared to those by conventional analyses. Results indicated that the post-processors were able to predict detailed stresses to a reasonable level of accuracy for woven-textile composites. The usefulness of the post-processor was demonstrated for a 5-harness satin-weave configuration.

Interface Failure at Ply Drops in CFRP/Sandwich Panels

This paper presents the results of an investigation of delamination failure at "exterior" ply drops in tension loaded sandwich panels with laminated composite face sheets. The thickness of composite laminates used as face sheets of sandwich panels is often increased locally around highly loaded locations such as joints, rivets, bolts or inserts. At the stations where such ply drops are made, the local bending stiffness of the face sheet laminates change discontinuously, thus inducing severe local bending effects. These local bending effects induce severe stress concentrations in the interfaces between the dropped plies/sub-laminates and the remaining face sheet laminates, and this may initiate delamination failure. The present paper suggests a simple approach for stress analysis and a simple "characteristic length" stress criterion for the prediction of delamination failure. An experimental investigation has been carried out, and the measured delamination loads compare well the theoretical predictions.

Stress Transfer from the Matrix to the Fibre in a Fragmentation Test: Raman Experiments and Analytical Modeling

The stress transfer properties of the fibre/matrix interface in the single fibre fragmentation test were investigated. Two carbon fibre-resin systems involving epoxysized and unsized fibres, were examined. Axial fibre stress data at resolutions of the order of one micron, were obtained with the technique of Remote Laser Raman Microscopy. Subsequent analytical modeling of the data was performed using a Bessel-Fourier Series stress analysis approach. The analysis provides a nearly exact solution for the stress field in the fragmentation test and simultaneously accounts for damaged or imperfect interfaces through the use of an interface parameter D, All data were fit using a two zone model in order to account for the propagation of interfacial damage as a function of applied strain. The fitting process was used to determine D(), the interface parameter in undamaged zones, Did), the interface parameter in the damage zones near fibre breaks, and Id, the length of the damage zones, all as a function of applied strain. The interface parameter in the undamaged zones, D('), was independent of applied strain. We claim D(')is a good property for comparing fibre/matrix interfaces and the most relevant property for predicting the role to the interface in real laminates.

Seismic design of reinforced-earth and soil-nailed structures

Soil-nailed and reinforced-earth structures are systems that are coherent and flexible. Therefore, they offer inherent advantages in withstanding large deformations and, as illustrated by post-earthquake observations on soil-nailed retaining structures and reinforced earth walls, they present high resistance to earthquake loading. Owing to these advantages soil-nailed and reinforced-earth structures offer a valuable and cost-effective technical solution for geotechnical construction in seismic zones. However, to date, only limited studies have been conducted to evaluate the dynamic response of these structures. This paper presents the development and experimental evaluation of kinematical pseudo-static working stress analysis approach for the seismic design of soil-nailed and reinforced-earth walls with inextensible metallic reinforcement. The proposed method is derived as an extension of the kinematical working-stress approach developed for the design of reinforced-earth and soil-nailed structures subjected to self-weight static loading. It provides an estimate of the seismic loading effect on the location and magnitude of maximum tension and shear forces developed in the reinforcements under working stress conditions. The method is evaluated through comparisons with experimental results of shaking-table tests on semi-scale reinforcedearth model walls and centrifugal soil-nailed model tests. The predictions of the method are also compared with numerical simulations of semi-scale shaking-table model test results. Finally, comparisons between the proposed method and currently available pseudo-static design methods are presented with preliminary conclusions with regard to design practice.

A finite element approach to the study of no-tension structures

A finite element approach for the approximate stress analysis of normal elastic no-tension bodies is presented. The proposed method is non-standard since it is based on a complementary energy theorem for elastic no-tension bodies proved by Giaquinta and Giusti in recent years. The numerical analysis reduces to a problem of minimization of a quadratic function with equality and inequality constraints; starting from a elementary stress field, an optimal approximate solution (safe in the spirit of limit analysis) is reached on employing the augmented Lagrangian method.

A fuzzy sets modelling approach for ergonomic workload stress analysis

The Ergonomic Workload Stress Index (EWSI) model was developed to predict the existence and level of the ergonomic workload stress via the concept of the fuzzy sets theory. The linguistic values (e.g., “heavy”, “uncomfortable”, etc.) of the tasks and workplace variables (e.g., physical job demand, postural, environmental stressors, etc.) which have most influential factors on stress were defined. The computerized system was developed to investigate the inappropriate tasks and workplaces and to suggest alternative solutions to problems. The EWSI model was implemented in three industrial environments (i.e., grocery store distribution warehouse, drilling tools manufacturer, and linen and uniform rental service industry) from the epidemiological and physiological viewpoints to validate the model. The following results were obtained from the validation process: (1) a positive relationship between the EWSI value and the severity of injury and illness rate (coefficient of correlation = 0.716, 0.917, and 0.854 for the three different industries); (2) a close linear relationship between the EWSI value and heart rate (coefficient of correlation = 0.845); and (3) a close linear relationship between the EWSI value and blood pressure (coefficient of correlation = 0.804 and 0.775 for the systotic and diastolic blood pressure, respectively).

A unified viscoplastic boundary element approach for residual stress analysis of axisymmetric bodies under axisymmetric and non-axisymmetric loads

This paper presents a unified viscoplastic boundary element method (BEM) for the residual stress analysis of axisymmetric structures subjected to axisymmetric and non-axisymmetric loads. By using the Fourier expansions of displacements, tractions and viscoplastic stresses including both the symmetric and anti-symmetric terms, the BEM formulations for an axisymmetric body subjected to axisymmetric and non-axisymmetric loads are developed. A unified viscoplastic model including the actual loading and unloading stress-strain material behaviour can be used to generate plasticity solutions in a simple manner when stationary conditions are reached, and at the other extreme, can reproduce standard creep phenomena. Hence, the viscoplastic BEM program developed in this paper for computing residual stresses of axisymmetric structures allows the treatment of a wide range of materially non-linear problems. The solution algorithm employed is relatively simple and possesses many advantages over the conventional computational procedures utilized in elastoplastic material analysis. Several examples of interest to residual stresses of axisymmetric structures due to axisymmetric and non-axisymmetric loads are presented.

A general finite element approach for contact stress analysis

This paper presents a general finite element approach for the treatment of contact stress problems. Stanctard shape function routines are used for the detection of contact between previously separate meshes and for the application of displacement constraints where contact has been identified. The mesh contact routines are installed in an incremental approach whereby the contact constraints are imposed by using either penalty functions or Lagrange multipliers.

A constrained, least squares approach for hybrid stress analysis of elastic bodies

The advent of computer technology has given rise to “new” solution methods in engineering. Finite element methods and boundary integral equation methods have been developed and used extensively by analysts simply because the computer allows one to model complex structures and obtain approximate solutions. An essential, yet difficult to quantify, part of the analysis of any structure is the estimation of the actual boundary conditions. The enclosed work investigates how one may use experimentally measured displacement data with random errors as a part of a hybrid approach to quantify the stresses in an elastic body under load. It is shown that by using measured displacement data, together with both a least squares approach for minimizing the effects of the measurement errors and also constraints to impose analytical requirements on the solution, the stresses throughout an elastic body can be computed with known accuracy, even in the presence of random displacement errors.

Note on the implementation of a continuum finite element approach for stress analysis in jointed rock : Carr, J.R. In: Research and Engineering Applications in Rock Masses (paper to the 26th US Symposium on Rock Mechanics, Rapid City, 26–28 June 1985)V1, P613–620. Publ Rotterdam: A. A. Balkema, 1985

Note on the implementation of a continuum finite element approach for stress analysis in jointed rock : Carr, J.R. In: Research and Engineering Applications in Rock Masses (paper to the 26th US Symposium on Rock Mechanics, Rapid City, 26–28 June 1985)V1, P613–620. Publ Rotterdam: A. A. Balkema, 1985

Interlaminar stress analysis for laminated plates containing a curvilinear hole

This study presents a variational-perturbation approach for the three-dimensional stress analysis around a curvilinear cutout in composite laminates. The solution is based on a composite expansion and assumed stress finite element methods. Stress field solutions for angleply and cross-ply laminates containing an elliptical hole have been presented. The effects of the ellipse aspect ratio and the fiber orientation on the interlaminar shear stress magnitude have been investigated. A failure criterion based on the interlaminar distortional energy function has been suggested. According to this criterion, it was found that, for angle-ply laminates containing an elliptical hole, a delamination failure initiation occurs at a point along the perpendicular to the direction of loading.

A Hybrid/Finite Element Approach for Stress Analysis of Notched Anisotropic Materials

A hybrid/finite element is proposed to calculate stresses or stress intensity factors at notches, fillets, cutouts, or other geometric discontinuities in plane-loaded anisotropic materials. Stress and displacement fields assumed in the element satisfy all governing elasticity equations. Furthermore, the shape and stress-free conditions of the discontinuity are modeled exactly using conformal mapping and analytic continuation. Continuity of analytic and finite element displacement fields on the remaining element boundary are enforced in an approximate manner with a variational principle. Numerical results are presented for both elliptical void and circular fillet hybrid elements. Comparisons are made to analytic solutions. Results indicate that structural models using a hybrid element with a coarse conventional element mesh yield efficient and accurate calculations of critical stresses.

A method for in vivo quantitative occlusal strain and stress analysis

A method to evaluate in vivo dental occlusal relationships by measuring strains and stresses, memorized in a thin wafer during occlusion, is presented. The method is based on the property of some polymers to memorize mechanical birefringence (the photoplastic phenomenon); it provides and records static and kinematic patterns related to the sequence of contacts during occlusion. This sequence determines the intensity levels of contacts according to impressions on the memorizing sheet. The method consists of observing and measuring, with an optical instrument, birefringence patterns appearing on a special memory sheet upon which a patient has occluded according to specific instructions. Two ways may be considered: the strain analysis and the stress analysis approach. The goal of the strain analysis approach is mostly clinical: to help attain harmonization of the static and kinematic occlusal patterns by detecting and eliminating prematurities and interferences through a step-by-step improvement of the strain uniformity. Other clinical uses include: Relating occlusal strain patterns to traumatic occlusion, bruxism or other functional disturbances. Diagnosing pain-dysfunction syndrome of supporting tissues in subjects with removable complete or partial dentures. Substantiating the comparative effect of supporting implants in combination with natural teeth in bridges, etc. The goal of the stress analysis approach is both clinical and theoretical, providing help in understanding the temporo-mandibular mechanical relationship.

Stress Analysis for Anisotropic Hardening in Finite-Deformation Plasticity

Kinematic hardening represents the anisotropic component of strain hardening by a shift of the center of the yield surface in stress space. The current approach in stress analysis at finite deformation includes rotational effects by using the Jaumann derivatives of the shift and stress tensors. This procedure generates the unexpected result that oscillatory shear stress is predicted for monotonically increasing simple shear strain. A theory is proposed that calls for a modified Jaumann derivative based on the spin of specific material directions associated with the kinematic hardening. This eliminates the spurious oscillation. General anisotropic hardening is shown to require a similar approach.

An approach for plane stress analysis of rectilinearly reinforced composites

The use of composite materials is gradually increasing in various industrial applications due to their many improved and fascinating properties. In the present investigation a general approach has been presented for solving the plane stress problems of rectilinearly orthotropic composites. The method essentially requires known values of boundary stresses at a number of preselected points. These boundary stresses are collocated in a least square sense to get a series which can be used for the determination of stresses at inside points. It is interesting to note that the error introduced in the analysis due to collocation of boundary stresses at some points reduces towards inner points. The method has been validated by applying it to a rectangular portion of the semi-infinite plane subjected to concentrated load and comparing the results at inside points with the exact ones.

The mechanics of dynamic shear crack propagation

A recent trend in seismology has been to model the earthquake source as a dynamically extending shear crack, and several basic concepts which seem to be important in this modeling process are examined. First, the universal spatial dependence of the plane elastodynamic stress and velocity fields near a sharp propagating crack tip is demonstrated for both subsonic and transsonic crack speeds, and the corresponding energy release rates are considered. Next, a class of steady state shear crack propagation problems is analyzed, based on both a direct stress analysis approach and an energy integral approach which obviates the need for a complete stress analysis in some cases. Several distinct stress differences which correspond to some of the common definitions of stress drop are involved in the analysis of these simple problems. Finally, some analytical considerations are presented which are relevant to rupture velocity determination for transient shear crack growth according to various fracture criteria, such as the critical stress intensity factor criterion, the critical energy release rate criterion, and the critical stress level criterion. Possible effects of spatially nonuniform stress drop and frictional resistance on rupture propagation are also discussed.

Mathematical and experimental studies on the mechanics of plated transverse fractures

A combined experimental and mathematical stress analysis approach to study the mechanics of a plated transverse fracture is described. Experimental results were obtained by placing strain gages on an equine third metacarpal and a bone plate. Two mathematical models for the mechanics of a bone and bone plate are presented. One is based on simple beam bending theory. The other is based on a more refined finite element representation for the deformations. Comparisons of experimental data and predicted results from the simple model are given and discussed. These comparisons provide a degree of confidence in the ability of a theoretical model to represent the actual deformations. The comparisons also show limitations of the simple beam model and the need for a more refined model such as a finite element representation. The resulting stress protection of the bone due to the bone plate and the percentage of load transferred through the plate are presented for a uniform loading condition. The advantages of a combined experimental and theoretical mechanics study are pointed out.

Global/local Approach Using Hybrid Elements For Composites

A global/local approach is proposed using partial hybrid elements for composites. The domain of the structure to be analyzed is divided into three areas: local region, global region, and transition region The 3-D sub-laminated elements are used to predict detail stress distribution in the local region The degenerated hybrid plate/shell element is used in the global region, and the transition elements are used to connect a degenerated element with the 3-D sublaminated elements. Because all of the elements in the global/local model are derived from the combined energy variational principle, the global/local finite element model satisfies the continuity of interlaminar stresses at the interlayer surface and traction condition on the top and bottom surface of laminated composites. Two examples are presented to show the efficiency and accuracy of the global/local approach for stress analysis of laminated composites.