Alexander Savaidis

Transient dynamic analysis of a cracked functionally graded material by a BIEM

A hypersingular time-domain traction boundary integral equation method (BIEM) is presented for transient dynamic crack analysis in a functionally graded material (FGM). A finite crack in an infinite and linear elastic FGM subjected to an impact antiplane crack-face loading is investigated. The spatial variation of the materials constants is described by an exponential law. To solve the hypersingular time-domain traction BIE, a numerical solution procedure is developed. The numerical solution procedure uses a convolution quadrature formula for approximating the temporal convolution and a Galerkin method for the spatial discretization of the hypersingular time-domain traction BIE. Numerical examples are presented to show the effects of the materials gradients on the dynamic stress intensity factors.

Elastic–plastic FE analysis of a notched shaft under multiaxial nonproportional synchronous cyclic loading

Abstract An elastic–plastic finite element analysis is presented for a notched shaft subjected to multiaxial nonproportional synchronous cyclic tension/torsion loading. The elastic–plastic material property is described by the von Mises yield criterion and the kinematic hardening rule of Prager/Ziegler. The finite element program system ABAQUS is used to solve the boundary value problem. Special emphasis is given to explore the effects of the stress amplitude, the mean-stress, and the mutual interactions on the local stress–strain responses at the notch root.

On size and technological effects in fatigue analysis and prediction of engineering materials and components

Abstract Analytical approaches concerning size, stress gradient and technological effects such as surface roughness and residual stresses induced during manufacturing processes are presented and discussed in this paper. Their implementation into the Short-Crack-Model for fatigue-life (lifetime to initiation of cracks of a size of 0.5– 1 mm ) prediction of engineering components subjected to cyclic loading is explained in detail. The procedures to consider the aforementioned effects are demonstrated by using an example of a forged and tempered steering shaft made of low-alloyed steel subjected to variable amplitude bend loading. The corresponding experimental results are used to check the accuracy of the analytical fatigue-life prediction. The comparison between analytically calculated and experimentally determined fatigue-life values emphasises the significance of technological effects (surface roughness, residual stresses) on fatigue-life estimation and the usefulness of the Short-Crack-Model for fatigue-resistant design of engineering components.

Elastic-plastic FE analysis of a notched cylinder under multiaxial nonproportional fatigue loading with variable amplitudes

Abstract This paper presents an elastic–plastic finite element (FE) analysis of an axisymmetric circular cylinder with a circumferential notch subject to multiaxial nonproportional fatigue loading with variable amplitudes. The von Mises yield criterion and the linear kinematic hardening rule of Prager–Ziegler are applied to describe the elastic–plastic material behavior. Two different loading combinations are considered: (1) constant tension with variable amplitude torsion; (2) variable amplitude tension with variable amplitude torsion. Numerical results for the local stress–strain curves at the notch-root are presented and discussed.

FE simulation of vehicle leaf spring behavior under driving manoeuvres

Purpose – The purpose of this paper is to develop a FE based modeling procedure for describing the mechanical behavior of high‐performance leaf springs made of high‐strength steels under damaging driving manoeuvres.Design/methodology/approach – The type and number of finite elements over the thickness of leaves, as well as the definition of contact, friction and clamping conditions, have been investigated to describe the mechanical behavior in an accurate and time‐effective manner. The proposed modeling procedure is applied on a multi‐leaf spring providing complex geometry and kinematics during operation. The calculation accuracy is verified based on experimental stress results.Findings – A FE based modeling procedure is developed to describe the kinematics and mechanical behavior of high‐performance leaf springs subjected till up to extreme driving loads. Comparison of numerically determined stress distributions with corresponding experimental results for a serial front axle multi‐leaf spring providing c...

Microstructural, surface and fatigue analysis of stress peened leaf springs

Purpose – The purpose of this paper is to investigate the fatigue and failure of commercial vehicle serial stress-peened leaf springs, emphasizing the technological impact of the material, the thermal treatment and the stress-peening process on the microstructure, the mechanical properties and the fatigue life. Theoretical fatigue analysis determines the influence of each individual technological parameter. Design engineers can assess the effectiveness of each manufacturing process step qualitatively and quantitatively, and derive conclusions regarding its improvement in terms of mechanical properties and fatigue life. Design/methodology/approach – Two different batches of 51CrV4 were examined to account for potential batch influences. Both specimen batches were subjected to the same heat treatment and stress-peening process. Investigations of their microstructure, hardness and residual stress state on the surface’ areas show the effect of the manufacturing process on the mechanical properties. Wohler cur...

Finite element simulation of road tanks for ADR and fatigue assessments

Purpose – The paper aims to illustrate the application of a state-of-the-art fatigue prediction concept (IIW recommendations) to the ADR calculation requirements, in order to include failure-critical weld details to the strength assessment of road tanks. The level of calculation accuracy and, therefore, safety of such structures transporting dangerous goods can be substantially increased. Design/methodology/approach – A case study of a 2-compartment aluminum alloy LBGF tank used for the transportation of gasoline/petroleum products is conducted adopting the meshing directives of the structural hot spot stress concept (SHSSC) of the IIW recommendations for the weld details of the structure. The stresses on the prescribed Hot Spots are extracted from the solutions of each load case described in the ADR legislation and assessed both in terms of static strength according to EN 14286 and fatigue strength using the standardized IIW assessment curves (FAT curves). Findings – The detailed analysis of the road tan...

A Unified Fatigue Life Calculation Model for Notched Components Based on Elastic-Plastic Fracture Mechanics

Based on Dankert’s et al. [1] initial model for the elastic-plastic evaluation of fatigue crack growth in sheets providing elliptical notches, a generalized procedure enabling an improved evaluation of the effective ranges of the crack driving force (i.e. the J-Integral) as well as the application to arbitrary notched components has been developed [2]. The present paper presents the basic topics of the calculation model as well as its verification using experimental results from notched specimens with various notch shapes subjected to cyclic loading with various load ratios.

Approximate elastic-plastic analysis of a notched bar under tensile and torsional fatigue

Abstract An approximate model is presented for estimating elastic–plastic stresses and strains in a notched bar subjected to synchronous non-proportional tensile and torsional cyclic loading. To begin with, it is applied to a multiaxial synchronous proportional loading system. A detailed FE analysis is performed for an axisymmetric bar of circular cross-section with a circumferential notch. The accuracy of the proposed approximate model is first established. The elastic–plastic material property is described by the von Mises yield criterion and a linear kinematic hardening rule. The comparison of the FE results with those estimated by the proposed approximate model shows good agreement for all loading cases investigated.

Evaluation of fatigue of fillet welded joints in vehicle components under multiaxial service loads

Abstract The mechanical behaviour and fatigue life of a thin-walled tube joined to a forged component by fillet welding is investigated theoretically and experimentally. The component is loaded by nonproportional random sequences of bending and torsion as measured during operation. The stresses in the welded structure are calculated using finite element analysis. The structure has been meshed following the IIW guideline for application of the hot spot stress approach. The fatigue lifetime of the welded structure is evaluated using the hot spot stresses in conjunction with the critical plane approach to account for multiaxial fatigue. Additionally, a model has been created to calculate fatigue lifetime based on local elastic stresses. The accuracy of the calculations is discussed using corresponding experimental fatigue life results.