Creep Finite elements

In the determination of the reference stress, JNC accounts for the creep strain intensity due to heterogeneous stress distribution in the ligament for small scale yielding condition. However, since the reeommended values of pi and p2 in eqn. (13) are based on creep finite element analyses for plates eontaining a through wall notch subjected to uniaxial tension, the applicability to the semi-elliptical surface crack has not been verified yet. 

The majority of polymer flow processes are characterized as low Reynolds number Stokes (i.e. creeping) flow regimes. Therefore in the formulation of finite element models for polymeric flow systems the inertia terms in the equation of motion are usually neglected. In addition, highly viscous polymer flow systems are, in general, dominated by stress and pressure variations and in comparison the body forces acting upon them are small and can be safely ignored. 

In this chapter, we have derived the two-dimensional finite element penalty formulation for creeping flows where the pressure was eliminated by assuming a compressible flow. Here, we will use a mixed formulation, where the pressure is included among the unknown variables. In the mixed formulation, we use different order of approximation for the pressure as we will for the velocity. For instance, if tetrahedral elements are used, we can use a quadratic representation for the velocity (10 nodes) and a linear representation for the pressure (4 nodes). Hence, we must use different shape functions for the velocity and pressure. For such a formulation we can write... 

Fig. 5.2 Comparison of creep behavior and time-dependent change in fiber and matrix stress predicted using a 1-D concentric cylinder model (ROM model) (solid lines) and a 2-D finite element analysis (dashed lines). In both approaches it was assumed that a unidirectional creep specimen was instantaneously loaded parallel to the fibers to a constant creep stress. The analyses, which assumed a creep temperature of 1200°C, were conducted assuming 40 vol.% SCS-6 SiC fibers in a hot-pressed SijN4 matrix. The constituents were assumed to undergo steady-state creep only, with perfect interfacial bonding. For the FEM analysis, Poisson s ratio was 0.17 for the fibers and 0.27 for the matrix, (a) Total composite strain (axial), (b) composite creep rate, and (c) transient redistribution in axial stress in the fibers and matrix (the initial loading transient has been ignored). Although the fibers and matrix were assumed to exhibit only steady-state creep behavior, the transient redistribution in stress gives rise to the transient creep response shown in parts (a) and (b). After Wu et al 1...

No attempt has been made to discuss, in a comprehensive manner, models which are based on finite element calculations or other numerical analyses. Only some results of Schmauder and McMeeking10 for transverse creep of power-law materials were discussed. The main reason that such analyses were, in general, omitted, is that they tend to be in the literature for a small number of specific problems and little has been done to provide comprehensive results for the range of parameters which would be technologically interesting, i.e., volume fractions of reinforcements from zero to 60%, reinforcement aspect ratios from 1 to 106, etc. Attention in this chapter was restricted to cases where comprehensive results could be stated. In almost all cases, this means that only approximate models were available for use. 

After the creep strain increment is calculated, the corresponding creep stress increment can be solved using finite element method. Song (2002). 

Numerical implementation of temperature and creep in mass concrete, Finite elements in analysis and design 37(2001) pp. 97-106 Vandewalle, L. 2000. 

The main advantage of using Eq. (2) is its availabihty in most commercial finite element codes. However, it does not include the reversible part of creep deformation, so a drop to zero of the applied stress due to load variations on the structure will not lead to back-deformation of the adhesive bond in a model. Viscoelastic material models containing time history must be used in such a case. 

In order to verify some of the predictive capabilities of the finite element model described in the previous sections, the transverse creep response of a IM7/5260 composite investigated in a earlier study [8] was used as a benchmark case. Two separate load histories were considered (1) transverse creep and recovery of a [90]i6 specimen under isothermal conditions, and (2) transverse creep of a [90]i6 specimen subjected to cyclic thermomechanical loading for extended periods of time. 

A comprehensive analytical model for predicting long term durability of resins and of fibre reinforced plastics (FRP) taking into account viscoelastic/viscoplastic creep, hygrothermal effects and the effects of physical and chemical aging on polymer response has been presented. An analytical tool consisting of a specialized test-bed finite element code, NOVA-3D, was used for the solution of complex stress analysis problems, including interactions between non-linear material constitutive behavior and environmental effects. 

Experimental data collection on the material, that can be used to perform accurate finite element numerical simulations of the trays. Two examples are statistical models for strength and constitutive equations of creep... 

You are designing a plastic chair with the aid of a finite-element program, and have chosen a toughened polypropylene for the application. Creep data for the material at 23°C are available in graphical form for space reasons, they are given here by the equation ... 

Kamiadakis and Beskok [6] developed a code H Flow with implementation of spectral element methods. They employed both the Navier-Stokes (incompressible and compressible) and energy equations in order to compute the relative effects of compressibility and rarefaction in gas microflow simulations. In addition, they also considered the velocity slip, temperature jump, and thermal creeping boundary conditions in the code Flow. The spatial discretization of fi Flow was based on spectral element methods, which are similar to the hp version of finite-element methods. A typical mesh for simulation of flow in a rough micro-channel with different types of roughness is shown in Fig. 1. The two-dimensional domain is broken up into elements, similar to finite elements, but each element employs high-order interpolants based on... 

Liu K, Ovaert TC (2011) Poro-viscoelastic constitutive modeling of unconfined creep of hydrogels using finite element analysis with integrated optimization method. J Mech Behav Biomed Mater 4 440-450... 

The Creep modeling procedure uses finite element methods to predict the time dependent deformation of structural ceramics at elevated temperatures. User-made creep subroutines using the theta projection method are under development. 

Because the reep effect may cause considerable stress redistribution in a component, the analyst must use the creep constants obtained in CARES with a finite element code (such as NASTRAN) to determine component deformation with time. 

Due to the redistribution of stresses, the evaluation of creep must be done with a finite element stress analysis code. However, a CARES module has been written for the data reduction of creep data... 

Keywords die swell, extrudate swell, blow molding, modelling of die swell, rheology, finite element modelling (FEM), creep fiber spinning. 

This chapter will discuss the testing, analysis, and design of structural adhesive joints. Adhesive bond test techniques to be considered include tensile, shear, peel, impact, creep, and fatigue. Some considerations will also be given to the effect of environment and test rate. A continuum approach to the analysis of adhesive joints will discuss tensile, shear, and peel stresses which arise in various joint geometries. Classical theories by Volkersen, Goland and Reissner, and others will be included. References to finite element analysis will be made where appropriate throughout the chapter. 

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