Purpose Finite Element Program Research Articles

Finite Element Based Investigation of Backfill Effects on Seismic Behavior of a Cantilever Wall

A series of finite element analyses were conducted to investigate the backfill effects on seismic behavior of a cantilever retaining wall incorporating backfill and subsoil interactions. Considering four different backfill soil conditions, the dynamic analyses of backfill-cantilever wall-soil/foundation system were carried out in time domain through ANSYS general purpose finite element computer program. The cohesionless soil was modelled as an elasto-plastic medium with viscous boundary applied on the artificial boundary of soil to simulate the wave energy absorption. Backfill-cantilever wall interface behavior was taken into account by using interface elements between the wall and soil to allow for de-bonding. The magnitudes of lateral displacements and stresses were determined. The obtained results show that the earthquake behavior of cantilever retaining walls can change considerably due to the backfill interaction. Thus, the backfill interaction should be considered in design criteria of cantilever walls.

Finite Element Modelling of Static and Fatigue Failure of Composite Repair System in Offshore Pipe Risers

The static and cyclic failure mechanisms of offshore pipe riser repaired with a designated laminate orientation of carbon/epoxy (C/E) system were studied. The finite element (FE) model takes into account failure mechanisms of the composite sleeve inter-layer delamination, debonding at the steel riser-composite surface interface, and the maximum permissible strain of the repaired riser. Design conditions of the combined static loads (coupled internal pressure, longitudinal tensile and transverse bending) were determined through a limit state analysis [1,2]. The limiting static bending load that causes catastrophic failure under a coupled internal pressure and tensile loadings was determined through Virtual Crack Closure Technique (VCCT). The effects of cyclic bending, mimicking the typical scenarios experienced in pipe riser exposed to dynamic subsea environment, were evaluated and compared against the static conditions. The low cycle fatigue of the composite repair system (CRS) is simulated using a direct cyclic analysis within a general purpose FE program, where the onset and fatigue delamination/disbonding growth are characterized through the Paris Law.

수직등분포하중을 받는 신형식단면 원형아치리브의 비선형 면내좌굴강도에 대한 해석연구

This paper investigates the characteristics of buckling loads for steel arches with new type cross section which is consisted of T-section and pipe-section. A general purpose finite-element program ABAQUS was used to evaluate the inelastic buckling strengths of the arches which included the influence of the geometric and material nonlinearity. According to the comparisons between earlier studies and results from finite-element analyses, new design equations should be developed for the new arches. New buckling factors were developed to consider influence of rise-to-span ratio and boundary conditions. It is found that the presented factors are sufficiently accurate to predict the inplane buckling loads of new type section steel arches subjected to uniformly distributed loading. The proposed equations can be used to investigate new type steel arches subjected to unsymmetrical loading and composited arches.

Transient hydrogen diffusion analyses coupled with crack-tip plasticity under cyclic loading

The effect of hydrogen on the material strengths of metals is known as the hydrogen embrittlement, which affects the structural integrity of a hydrogen energy system. In the present paper, we developed a computer program for a transient hydrogen diffusion–elastoplastic coupling analysis by combining an in-house finite element program with a general purpose finite element computer program to analyze hydrogen diffusion. In this program, we use a hypothesis that the hydrogen absorbed in the metal affects the yield stress of the metal. In the present paper, we discuss the effects of the cyclic loading on the hydrogen concentration near the crack tip. An important finding we obtained here is the fact that the hydrogen concentration near the crack tip greatly depends on the loading frequency. This result indicates that the fatigue lives of the components in a hydrogen system depend not only on the number of loading cycles but also on the loading frequency.

Transient Hydrogen Diffusion-Elastoplastic Coupling Analysis near a Blunting Crack Tip

The effect of hydrogen on the metals is known as hydrogen embrittlement, which affects the structural integrity of a hydrogen energy system. Hydrogen atoms near a crack tip play an important role in the hydrogen embrittlement. In the present paper, we developed a computer program for an transient hydrogen diffusion-elastoplastic coupling analysis by combining an in-house finite element program for hydrogen diffusion analysis with a general purpose finite element computer program for stress analysis. In the hydrogen diffusion equation, we consider both the hydrogen concentration at the normal interstitial lattice sites and that at the trap sites, and also take account of hydrogen diffusion flux due to hydrostatic stress. We use a hypothesis that the hydrogen absorbed in the metal affects the yield stress of the metal. Therefore, the hydrogen diffusion problem is coupled with the elastoplastic stress problem. Using the computer program developed in the present study, we performed the transient hydrogen diffusion-elastoplastic coupling analysis of a cracked plate made of a bcc-metal, and obtained the hydrogen concentration, hydrostatic stress and plastic strain near the crack tip. In the present paper, we discuss the effects of the initial hydrogen concentration, the boundary condition of hydrogen on the free surface and the loading frequency. An important finding obtained from the present study is the fact that the hydrogen concentration near the crack tip depends greatly on the loading frequency. The fact indicates that the fatigue lives of the components in a hydrogen system depend not only on the number of loading cycles but also on the loading time.

Deflection Response Models for Cracked Rigid Pavements

The static elastic layer model is customarily used for analyzing deflection measurements and back-calculating pavement layer moduli. Estimation of in-situ layer moduli by means of a mechanistically based iterative technique is known as back-calculation. Despite the fact that the falling weight deflectometer (FWD) load induces a dynamic load, dynamic/impact analysis routines are seldom, because of the mathematical complexity. Dynamic deflection prediction models are developed in this study, which can be used in back-calculation routines. The first step in accomplishing this is to select an appropriate analysis model for which ABAQUS, a general purpose finite-element program, is used. Static and dynamic deflection responses from the ABAQUS model of an uncracked pavement are validated. Following this first step, cracks and joints along with other features of the pavement are modeled in addition to nonlinear behavior of pavement materials. Deflection responses of cracked pavement under a series of increasing loads, assuming linear and nonlinear behavior of base, subbase, and subgrade materials, are computed and compared. After finalizing the model, a synthetic deflection database, specifically with FWD load, is developed relying on a fractional factorial design layout in which thicknesses, layer moduli, and cracks are allowed to vary over a range. Making use of this database, regression equations that predict surface deflection bowls in terms of layer moduli and thicknesses are developed. Deflection equations are validated using field data from two in-service pavements.

A two-surface cyclic plasticity model consistent with fundamental stress-strain equations of the power-law type

A plasticity constitutive model which can describe primary features of stress-strain behaviors of cyclically loaded metallic materials under isothermal conditions is developed in the framework of the two-surface plasticity theory. A special plastic hardening modulus function, which is consistent with the power-law type stress-strain expressions frequently used for both monotonic and cyclic stable stress-strain curves, is introduced to represent cyclic hardening as well as saturated behaviors more realistically. The model is validated through its application to the simulation of uniaxial cyclic and biaxial behaviors of cyclic hardening materials. This model is then implemented into a general purpose finite element computer program and applied to the analysis of a notched plate subjected to cyclic loading.

An equivalent domain integral method for three-dimensional mixed-mode fracture problems

A general formulation of the equivalent domain integral (EDI) method for mixed-mode fracture problems in cracked solids is presented. The method is discussed in the context of a 3-D finite-element analysis. The J- integral consists of two parts: the volume integral of the crack front potential over a torus enclosing the crack front and the crack surface integral due to the crack front potential plus the crack-face loading. In mixed-mode crack problems the total J- integral is split into J I , J II , and J III , representing the severity of the crack front in three modes of deformation. The direct and decomposition methods are used to separate the modes. These two methods were applied to several mixed-mode fracture problems in isotropic materials. Several pure and mixed-mode fracture problems were analyzed and results found to agree well with those available in the literature. The method lends itself to be used as a post-processing subroutine in a general purpose finite-element program.

Stress analysis method for clearance-fit joints with bearing-bypass loads

Within a multi-fastener joint, fastener holes may be subjected to the combined effects of bearing loads and loads that bypass the hole to be reacted elsewhere in the joint. The analysis of a joint subjected to search combined bearing and bypass loads is complicated by the usual clearance between the hole and the fastener. A simple analysis method for such clearance-fit joints subjected to bearing-bypass loading has been developed in the present study. It uses an inverse formulation with a linear elastic finite-element analysis. Conditions along the bolt-hole contact arc are specified by displacement constraint equations. The present method is simple to apply and can be implemented with most general purpose finite-element programs since it does not use complicated iterative-incremental procedures. The method was used to study the effects of bearing-bypass loading on bolt-hole contact angles and local stresses. In this study, a rigid, frictionless bolt was used with a plate having the properties of a quasi-isotropic graphite/epoxy laminate. Results showed that the contact angle as well as the peak stresses around the hole and their locations were strongly influenced by the ratio of bearing and bypass loads. For single contact, tension and compression bearing-bypass loading had opposite effects on the contact angle. For some compressive bearing-bypass loads, the hole tended to close on the fastener leading to dual contact. It was shown that dual contact reduces the stress concentration at the fastener and would, therefore, increase joint strength in compression. The results illustrate the general importance of accounting for bolt-hole clearance and contact to accurately compute local bolt-hole stresses for combined bearings and bypass loading.

Adaptivity in hybrid‐Trefftz finite element formulation

AbstractWith the advent of computer aided design (CAD), the development of fully or semi‐automated procedures by which a solution warranting the specified accuracy can most efficiently be reached has become a necessity. It is now of utmost interest to investigate finite element (FE) formulations offering a simple form of adaptivity, easy to implement.The present study (which is a sequel to an earlier paper1 on error estimation by the authors) identifies as a particularly promising approach of attaining this goal the p‐method associated with the so‐called hybrid‐Trefftz FE model.2 Based on a simple stress error estimator1 and prior knowledge of the convergence rate, the solution warranting specified stress accuracy may be reached in a single trial by suitably respecifying just one parameter in the input data. The reported approach has successfully been implemented into the general purpose FE program SAFE3 and its high efficiency is illustrated in the paper through practical applications involving corner singularities and stress concentrations.

Selection of Degrees of Freedom for Dynamic Analysis

A technique for the selection of dynamic degrees of freedom (DDOF) of large, complex structures for dynamic analysis is described and the formulation of Ritz basis vectors for static condensation and component mode synthesis is presented. Generally, the selection of DDOF is left to the judgment of engineers. For large, complex structures, however, a danger of poor or improper selection of DDOF exists. An improper selection may result in singularity of the eigenvalue problem, or in missing some of the lower frequencies. This technique can be used to select the DDOF to reduce the size of large eigenproblems and to select the DDOF to eliminate the singularities of the assembled eigenproblem of component mode synthesis. The execution of this technique is discussed in this paper. Examples are given for using this technique in conjunction with a general purpose finite element computer program GENSAM[1].

Investigation of Thermal Effects on Weapon System Components

A three-dimensional stress analysis of a 30-mm machine gun component on the Harrier Aircraft was conducted to investigate the cause of observed fractures. The analysis was made using a general purpose finite element computer program and a laboratory environmental test chamber. Based on this study, the probable cause of failure was identified and, as a result, the component manufacturer is considering possible design changes to alleviate this problem in further production. The study clearly demonstrates that computer-based technology can be successfully used in investigating causes of failure in complex structural components.

Contact problems with friction in general purpose finite element computer programs

A combined incremental and iterative procedure for analysis of elastostatic contact problem is presented. The method suggested may with rather small efforts be implemented in any general purpose finite element computer program. Most of the routines required by the method do already exist in a general finite element routine library. Examples of modules required are multilevelled substructuring, structural stiffness matrix assembly routines and a solver for symmetric system matrices. A wide class of ordinary elements can be used in the discretization of the the contact surfaces. Only translational freedoms are treated as unknowns in the iterative procedure. The accuracy and efficiency of the method has been verified in several applications as for example three-dimensional roller bearing calculations and shear loaded bolted joints.