Stress-strain Approach Research Articles

A verification of the assumption of anti-fatigue design

In this paper, the approaches of anti-fatigue design are briefly reviewed and are classified into three groups: nominal stress approach, local stress–strain approach and stress field intensity approach. Two types, each with two notches, are specially designed and a total of 30 specimens with 4 dimensions are tested under different constant–amplitude loading. These specimens are also analysed with elasto-plastic FEM to obtain stress–strain distributions and stress concentration factors. Fatigue life is estimated based on the different approaches. Experimental and analytical results show that the assumption of stress field intensity is more reasonable than that of the other approaches.

On the Response of a Sandwich Panel with a Bilinear Core

Sandwich panels can failin a variety of ways. In the present article one type of failure is investigated and modeled that has a number of important applications, e.g., marine hulls. Here core yielding is assumed to initiate and grow in the sandwich panel while the face sheets remain bonded, unbuckled, and in the elastic range. For elastic face sheets, the core shear stresses can be determined from equilibrium of the face sheets independent of core yield. Core shear strains can then be found from the stress-strain curve and an algorithm is constructed for determining shear deflection. Bending deflection is found from the elastic solution. This approach works well except when the bilinear stress-strain behavior approaches the perfectly plastic core. With the aid of a detailed finite-element solution, it is shown that the classical sandwich theory assumptions begin to break down and that the face sheets now carry an appreciable part of the shear load. This effect is shown in detail for four-point beam bending, for which the classical sandwich solution is 20-30% below the ABAQUS results and the experimental data. For the bilinear case, not close to perfectly plastic, however, the extension of the classical theory to the coreyielding problem provides excellent results.

A new approach to the determination of fatigue crack initiation size

In this paper, the definition of fatigue crack initiation size and determining method were presented on the basis of the non-propagating cracks behaviour. The physical significance of fatigue crack initiation size was explained from the point of view of the fatigue damage. Fatigue crack initiation size is obtained by predicting a non-propagating crack at the notch root under fatigue limit loading. On the basis of the fatigue crack initiation size determined in this paper, the fatigue crack initiation life was predicted by means of the local stress–strain approach, under both constant amplitude and random loading, and good agreement is demonstrated with experimental data.

Fatigue analysis and the local stress–strain approach in complex vehicular structures

In the last 20years the `strain-life' fatigue analysis philosophy has achieved the status of industry standard in the automotive, truck and earth moving industries in North America. Although the fundamental concepts of the method are quite simple, the recent massive computerization of the techniques, and their incorporation into large dynamically loaded body and chassis durability calculation models, has resulted in new capabilities and insights for engineers, but also has meant new challenges for the creators of fatigue simulation software.This paper gives a brief history of the evolution of this type of calculation software in the vehicular industry from the observation of stress–strain hysteresis behavior, through the early development of computer versions of the stress–strain shape and memory models, to their evolution into routines that are closely linked to vehicle dynamics models that calculate loads in structures, finite element models that transform the loads into local stresses, and subsequent plasticity correction and damage evaluation routines which yield expected life color contour plots for vehicle body and chassis.

The estimation of J in three-point-bend specimens with a crack in a mismatched weld

The J integral is estimated by using an equivalent stress-strain relationship approach for three-point-bend specimens containing a weld with mismatched mechanical properties. Elastic-plastic finite element analyses are performed to verify the use of this approach. The results show that satisfactory precision can be obtained provided a suitable limit load solution is used. A limit load solution suggested by Burstow is suitable for over-matching situations and a solution due to Joch et al. for under-matching ones.

A new damage parameter for fatigue life predictions under local strain analysis

A new damage parameter is proposed for fatigue life prediction using a local stress-strain approach. This parameter has a physical energy basis, and makes it possible to obtain the same accuracy as, and better life assessments than, the well-known Smith et al parameter using significantly less calculation time for load history treatment. Comparisons of life predictions obtained using the proposed parameter with experimental results and other predictions are presented.

Stress field intensity approach for predicting fatigue life

In this paper a new design approach for predicting fatigue life—the stress field intensity approach—is presented from the point of view of macromechanics on the basis of the mechanism of fatigue damage of metals. In this new approach the stress field intensity over the local region of damage, instead of the stress peak value as in the local stress-strain approach, was taken as the parameter with which to measure the fatigue strength of structures. Many fatigue phenomena, which the nominal stress approach and the local stress-strain approach could not explain, can be explained reasonably in this new approach.

Fatigue crack growth in 5083 aluminum alloy under varying loading conditions: Takaai, T. and Nakayama, Y. J. Jpn Inst. Met. Jan. 1992 42 (1) 45–51 (in Japanese)

In this paper a new design approach for predicting fatigue life—the stress field intensity approach—is presented from the point of view of macromechanics on the basis of the mechanism of fatigue damage of metals. In this new approach the stress field intensity over the local region of damage, instead of the stress peak value as in the local stress-strain approach, was taken as the parameter with which to measure the fatigue strength of structures. Many fatigue phenomena, which the nominal stress approach and the local stress-strain approach could not explain, can be explained reasonably in this new approach.

Prediction of fatigue crack initiation lives for welded plate T-joints based on the local stress-strain approach

The predicted fatigue crack initiation lives of welded plate T-joints in air and seawater environments are reported and compared with experimental data from Canadian offshore steel research. Estimation of initiation lives are based on the local stress-strain approach. The effects of plate thickness on predicted fatigue crack iives are discussed.

A notch stress-strain analysis approach to fatigue crack growth

A model of fatigue crack growth based on elastic-plastic notch stress-strain analysis has been presented. It was assumed that the fatigue crack can be analysed as a notch with the tip radius ρ ∗ . It was also assumed that the material was composed of elemental blocks of a finite linear dimension ρ ∗ . The fatigue crack growth was regarded as an increment of successive crack reinitiation over the distance ρ ∗ from the crack tip. The number of cycles N ∗ necessary to fracture the material over the distance ρ ∗ was calculated from the Manson-Coffin strain-life relation. The near-crack tip elasticplastic stress and strain were calculated on the basis of the elastic solution for blunt cracks and energy density criterion derived earlier by the author. Both the near-crack tip mean stress and the fatigue damage accumulation in the material beyond the process zone were included into the analysis. The calculations were based on effective stress intensity range. It was shown that the fatigue crack growth rate in the linear and near-threshold region of the da dN vs ΔK curve can be deducted on the basis of the proposed model and the smooth specimens material data. The effective threshold stress intensity range can be determined also. The theoretical results were compared with the experimental data obtained from three different alloy steels. Good agreement was achieved in both the near-threshold and linear range of the da dN vs ΔK curve.

Mechanical Properties of the Plasma Membrane of Isolated Plant Protoplasts

The volume of isolated protoplasts of rye (Secale cereale L. cv Puma) in a suspending solution at constant concentration is shown to be negligibly changed by tensions in the plasma membrane which approach that tension necessary to lyse them. This allows a detailed investigation of the plasma membrane stress-strain relation by micropipette aspiration.Over periods less than a second, the membrane behaves as an elastic two-dimensional fluid with an area modulus of elasticity of 230 millinewtons per meter. Over longer periods, the stress-strain relation approaches a surface energy law-the resting tension is independent of area and has a value of the order 100 micronewtons per meter. Over longer periods the untensioned area, which is defined as the area that would be occupied by the molecules in the membrane at any given time if the tension were zero, increases with time under large imposed tensions and decreases under sufficiently small tension. It is proposed that these long term responses are the result of exchange of material between the plane of the membrane and a reservoir of membrane material. The irreversibility of large contractions in area is demonstrated directly, and the behavior of protoplasts during osmotically induced cycles of contraction and expansion is explained in terms of the membrane stress-strain relation.

Prediction of Random High-Cycle Fatigue Life of LWR Components

This state-of-the-art review identifies and discusses the existing methods of predicting the high-cycle fatigue life, their limitations, and base-technology needs. The cycle stress-strain approach and the random vibration approach are reviewed, evaluated and discussed. It is applicable to estimating high-cycle fatigue damages of Light Water Reactor (LWR) components under the random excitation typical of flow-induced vibration.