Inelastic Analysis of Components Using a Modulus Adjustment Scheme

1998 ◽  
Vol 120 (1) ◽  
pp. 1-5 ◽  
Author(s):  
S. Babu ◽  
P. K. Iyer
Keyword(s):  
Low Cycle Fatigue ◽  
Inelastic Strain ◽  
Robust Methods ◽  
Element Analysis ◽  
Linear Elastic ◽  
Inelastic Analysis ◽  
Inelastic Strains ◽  
Adjustment Scheme ◽  
Inelastic Region ◽  
Modulus Reduction

Mechanical components and structures loaded into inelastic region can fail by low cycle fatigue (LCF). Evaluation of inelastic strain is an important stage in the LCF life prediction methodology. Different techniques, viz., experimental methods, elastic-plastic finite element analysis (FEA), and robust methods, can be used to predict inelastic strains. The state predicted by available robust methods does not correspond to equilibrium state of the component. A method called MARS (modulus adjustment and redistribution of stress) based on linear elastic FEA has been developed to obtain equilibrium and kinematic distributions close to the actual one. The proposed method uses an iterative strategy combined with a modulus reduction technique.

A Robust Method for Inelastic Analysis of Components Made of Anisotropic Material

1999 ◽  
Vol 121 (2) ◽  
pp. 154-159 ◽  
Author(s):  
S. Babu ◽  
P. K. Iyer
Keyword(s):  
Finite Element ◽  
Anisotropic Material ◽  
Robust Method ◽  
Element Analysis ◽  
Linear Elastic ◽  
Inelastic Analysis ◽  
Anisotropic Bodies ◽  
Inelastic Strains ◽  
Adjustment Scheme ◽  
Good Agreement

A new robust method, called MARS (modulus adjustment and redistribution of stress), based on linear elastic finite element analyses has been proposed to evaluate inelastic strains in anisotropic bodies. The linearity of relaxation locus forms the basis of the method. A combination of modulus adjustment scheme and iterative strategy used in the MARS method satisfies the equilibrium and yield conditions, which in turn brings the static and kinematic distributions close to the actual distributions for a given load. Several notched bodies made of anisotropic material are analyzed using the MARS method and the inelastic strains evaluated are found to be in good agreement with those predicted using elastic-plastic finite element analysis.

A Highly Accelerated Thermal Cycling (HATC) Test for Solder Reliability Assessment in BGA Packages

2007 ◽  
Author(s):  
X. Long ◽  
I. Dutta ◽  
R. Guduru ◽  
R. Prasanna ◽  
M. Pacheco
Keyword(s):  
Thermal Cycling ◽  
Solder Joints ◽  
Low Cycle Fatigue ◽  
Inelastic Strain ◽  
Fatigue Reliability ◽  
Element Analysis ◽  
Mechanical Cycling ◽  
Experimental Apparatus ◽  
Dependent Strain ◽  
Accelerated Thermal Cycling

A thermo-mechanical loading system, which can superimpose a temperature and location dependent strain on solder joints, is proposed in order to conduct highly accelerated thermal-mechanical cycling (HATC) tests to assess thermal fatigue reliability of Ball Grid Array (BGA) solder joints in microelectronics packages. The application of this temperature and position dependent strain produces generally similar loading modes (shear and tension) encountered by BGA solder joints during service, but substantially enhances the inelastic strain accumulated during thermal cycling over the same temperature range as conventional ATC (accelerated thermal cycling) tests, thereby leading to a substantial acceleration of low-cycle fatigue damage. Finite element analysis was conducted to aid the design of experimental apparatus and to predict the fatigue life of solder joints in HATC testing. Detailed analysis of the loading locations required to produce failure at the appropriate joint (next to the die-edge ball) under the appropriate tension/shear stress partition are presented. The simulations showed that the proposed HATC test constitutes a valid methodology for further accelerating conventional ATC tests. An experimental apparatus, capable of applying the requisite loads to a BGA package was constructed, and experiments were conducted under both HATC and ATC conditions. It is shown that HATC proffers much reduced cycling times compared to ATC.

Fatigue Life Modeling of Anisotropic Materials Using a Multiaxial Notch Analysis

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Z. J. Moore ◽  
R. W. Neu
Keyword(s):  
Fatigue Life ◽  
Elevated Temperatures ◽  
Low Cycle Fatigue ◽  
Inelastic Strain ◽  
Anisotropic Materials ◽  
Equivalent Strain ◽  
Strain Response ◽  
Element Analysis ◽  
Anisotropic Elastic ◽  
Notch Analysis

Fatigue life modeling of anisotropic materials such as directionally-solidified (DS) and single-crystal Ni-base superalloys is often complicated by the presence of notches coupled with dwells at elevated temperatures. This paper focuses on an approach for predicting low cycle fatigue that includes notch geometry effects while taking into consideration material orientation. An analytical model based on a generalization of the Neuber notch analysis to both multiaxial loading and anisotropic materials is used to determine the localized stress-inelastic strain response at the notch. The material anisotropy is captured through a multiaxial generalization of the Ramberg–Osgood relation using a Hill’s criterion. The elastic pseudo stress and pseudo strain response in the vicinity of the notch used as input in the Neuber analysis is determined from an anisotropic elastic finite element analysis. The effects of dwells at elevated temperature are captured using an equivalent strain rate. A nonlocal approach is needed to correlate the life of notched specimens to smooth specimens.

Fatigue Life Estimation Method Considering Inelastic Behavior of Ni-Based Directionally Solidified Superalloy With Multiple Holes

2012 ◽  
Author(s):  
Takashi Yokoyama ◽  
Masaru Sekihara
Keyword(s):  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Estimation Method ◽  
Inelastic Strain ◽  
Maximum Tensile Stress ◽  
Fatigue Tests ◽  
Inelastic Behavior ◽  
Cycle Fatigue ◽  
Directionally Solidified ◽  
Element Analysis

Low cycle fatigue tests at high temperature were conducted on test specimens with small holes made of a Ni-based directionally solidified superalloy, which are intended as the cooling structures formed in the components in the fossil fuel power plant. The tests included those cases with and without a strain holding process, i.e., fatigue creep interaction (FCI) tests and low cycle fatigue (LCF) tests, respectively. The number of LCF crack initiation cycles of the one- and seven-hole specimens decreased compared to that of the smooth one. The number of FCI crack initiation cycles of a compressive hold case for the seven-hole specimen decreased compared to that of the LCF test, while that of a tensile hold case decreased further. The test results were evaluated based on the inelastic behavior around the center hole of the specimens, where the most serious inelastic strain occurred, using finite element analysis that takes into account the inelastic anisotropy of material properties. The number of crack initiation cycles of the LCF and the compressive FCI tests correlated with the maximum tensile stress around the hole, while that of all the tests correlated with the frequency-modified strain energy. We propose a method for evaluating cyclic inelastic behavior around a hole using cyclic Neuber’s rule for anisotropic materials to simply evaluate the failure life of actual components.

Simplified Inelastic Time Independent (SITI) Method for Predicting Creep

2007 ◽  
Author(s):  
Jeries J. Abou-Hanna ◽  
Osama Ali ◽  
Venkata Tatikonda ◽  
Timothy E. McGreevy
Keyword(s):  
Creep Behavior ◽  
Inelastic Strain ◽  
Material Model ◽  
Time Dependent ◽  
Computationally Efficient ◽  
Element Analysis ◽  
State Variable ◽  
Creep Analysis ◽  
Inelastic Strains ◽  
Very High

In an effort to address inelastic creep behavior for very high temperature (VHT) applications, a unified state variable material model was used in a time dependent finite element analysis to generate isochronous curves. The resulting isochronous curves were then used in an efficient time-independent plastic analysis to predict the creep behavior of components. This simplified inelastic time-independent (SITI) method can significantly reduce the geometric and load uncertainties, and the over-conservatism in predicting inelastic strain levels. SITI is an effective and computationally efficient approach for predicting inelastic strains of components operating at high and very high temperatures such as the case in the Next Generation Nuclear Plant. This work compares the SITI inelastic strains to those obtained using fully inelastic time-dependent elastic-plastic-creep analysis, and illustrates the effectiveness of the approach in obtaining creep strain predictions without elaborate full inelastic time-dependent simulation.

The Generalized Local Stress Strain (GLOSS) Analysis—Theory and Applications

1991 ◽  
Vol 113 (2) ◽  
pp. 219-227 ◽  
Author(s):  
R. Seshadri
Keyword(s):  
Stress Relaxation ◽  
Low Cycle Fatigue ◽  
Creep Damage ◽  
Local Stress ◽  
Inelastic Strain ◽  
Uniaxial Stress ◽  
Linear Elastic ◽  
Analysis Theory ◽  
Stress Classification

GLOSS analysis is a simple and systematic method for carrying out inelastic evaluations of mechanical components and structures on the basis of two linear elastic finite element analyses. The underlying theory relates redistribution of inelastic stresses at a given location under consideration to the uniaxial stress relaxation process. GLOSS analysis is emerging as a useful technique for determining multiaxial stress relaxation, follow-up, creep damage, inelastic strain concentrations and low-cycle fatigue estimates, limit analysis and issues pertaining to stress-classification.

Robust Approximate Methods for Estimating Inelastic Fracture Parameters

1995 ◽  
Vol 117 (2) ◽  
pp. 115-123 ◽  
Author(s):  
R. Seshadri ◽  
R. K. Kizhatil
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Creep Crack Growth ◽  
Growth Parameter ◽  
Local Stress ◽  
Robust Methods ◽  
Approximate Methods ◽  
Element Analysis ◽  
Linear Elastic ◽  
Good Agreement

Robust approximate methods to estimate the inelastic energy release rate J, and the creep crack-growth parameter, C*, for cracked components are described in this paper. These methods use linear elastic finite element analysis in conjunction with the concepts of the generalized local stress strain (GLOSS) analysis and redistribution nodes (r-nodes), and are readily applicable to complex geometries and loadings. J-estimates obtained by the use of robust methods are found to be in good agreement with the results of elastic-plastic finite element analysis.

Fatigue Failure Analysis Using the Theory of Critical Distance

2011 ◽  
Vol 462-463 ◽  
pp. 663-667 ◽  
Author(s):  
Ruslizam Daud ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Al Emran Ismail
Keyword(s):  
Stress Concentration ◽  
Fatigue Failure ◽  
Notch Root ◽  
High Stress ◽  
Critical Distance ◽  
Future Research ◽  
Element Analysis ◽  
Linear Elastic ◽  
The Finite Element Analysis ◽  
Elastic Fracture

This paper explores the initial potential of theory of critical distance (TCD) which offers essential fatigue failure prediction in engineering components. The intention is to find the most appropriate TCD approach for a case of multiple stress concentration features in future research. The TCD is based on critical distance from notch root and represents the extension of linear elastic fracture mechanics (LEFM) principles. The approach is allowing possibilities for fatigue limit prediction based on localized stress concentration, which are characterized by high stress gradients. Using the finite element analysis (FEA) results and some data from literature, TCD applications is illustrated by a case study on engineering components in different geometrical notch radius. Further applications of TCD to various kinds of engineering problems are discussed.

Strength envelope of granular soil stabilized by multi-axial geogrid in large triaxial tests

2020 ◽  
Vol 57 (3) ◽  
pp. 448-452 ◽  
Author(s):  
A.S. Lees ◽  
J. Clausen
Keyword(s):  
Triaxial Compression ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Failure Envelope ◽  
Element Analysis ◽  
Linear Elastic ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic ◽  
Triaxial Compression Tests ◽  
Properties Of Soil

Conventional methods of characterizing the mechanical properties of soil and geogrid separately are not suited to multi-axial stabilizing geogrid that depends critically on the interaction between soil particles and geogrid. This has been overcome by testing the soil and geogrid product together as one composite material in large specimen triaxial compression tests and fitting a nonlinear failure envelope to the peak failure states. As such, the performance of stabilizing, multi-axial geogrid can be characterized in a measurable way. The failure envelope was adopted in a linear elastic – perfectly plastic constitutive model and implemented into finite element analysis, incorporating a linear variation of enhanced strength with distance from the geogrid plane. This was shown to produce reasonably accurate simulations of triaxial compression tests of both stabilized and nonstabilized specimens at all the confining stresses tested with one set of input parameters for the failure envelope and its variation with distance from the geogrid plane.

Component Low Cycle Fatigue Behavior Based on Standard Calculation Procedure and Non-Linear FEA

2017 ◽  
Author(s):  
Jürgen Rudolph ◽  
Adrian Willuweit ◽  
Steffen Bergholz ◽  
Christian Philippek ◽  
Jevgenij Kobzarev
Keyword(s):  
Power Plants ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Hybrid Approach ◽  
Combined Cycle ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Constitutive Material Model ◽  
Standard Design ◽  
Creep Fatigue

Components of conventional power plants are subject to potential damage mechanisms such as creep, fatigue and their combination. These mechanisms have to be considered in the mechanical design process. Against this general background — as an example — the paper focusses on the low cycle fatigue behavior of a main steam shut off valve. The first design check based on standard design rules and linear Finite Element Analysis (FEA) identifies fatigue sensitive locations and potentially high fatigue usage. This will often occur in the context of flexible operational modes of combined cycle power plants which are a characteristic of the current demands of energy supply. In such a case a margin analysis constitutes a logical second step. It may comprise the identification of a more realistic description of the real operational loads and load-time histories and a refinement of the (creep-) fatigue assessment methods. This constitutes the basis of an advanced component design and assessment. In this work, nonlinear FEA is applied based on a nonlinear kinematic constitutive material model, in order to simulate the thermo-mechanical behavior of the high-Cr steel component mentioned above. The required material parameters are identified based on data of the accessible reference literature and data from an own test series. The accompanying testing campaign was successfully concluded by a series of uniaxial thermo-mechanical fatigue (TMF) tests simulating the most critical load case of the component. This detailed and hybrid approach proved to be appropriate for ensuring the required lifetime period of the component.

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