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The major problems due to welding effects are the residual stresses and distortions of which the levels affect more or less the resistance and lifetime of welded structure. In steel industry and particularly in shipbuilding, during these last few decades, thin plates are used more and more in ship construction in order to lighten the structure weight. Unfortunately, excessive distortions occurred on these thin stiffened panels and straightening works must be executed in respecting the limit tolerance fixed by the Quality Standard of Ship Construction. These futil works reduce Productivity and Quality, increase Construction Cost and get longer Fabrication Delay. Thus, it is necessary to evaluate, control and minimize the distortion and stress levels of thin welded panels before welding assembly operations. In this paper, a short presentation of the Methodology and its industrial applications in shipbuilding are presented for two panels of a Chemical Parcel Tanker (1996) and a large ‘‘Testing’’ Panel in full scale of a Passsengers Ship (2002). The numerical results due to welding effects so obtained within short computer-time (three hours and half for a 3D FE model of more than two million of degrees of freedom) ) on a linear FEM software were verified with measured stress values and identified with the buckling state of the ‘‘Testing’’ Panel before and after welding operations by photographies.

The aim of the study was to evaluate the residual stresses in polymer – ceramic composites using the Finite Element Method (FEM). The effect of the composite structure on the residual stresses built up was also analyzed.

The aim of the article is to study and develop welding numerical models in the phase transformation and damage condition. The models are based on the study of damage concept in the multiphasic behavior, which occurs by welding process. The core of models or constitutive equations is the coupling between ductile damage, small strain elasticity, finite visco-plasticity and phase transformation. Based on the theory of thermodynamics and continuum damage mechanics (CDM), constitutive equations are built to describe damage growth and crack appearance during and after welding. The thermodynamics of irreversible processes with state variables is used as a framework to develop the phase coupling model. The related numerical aspects concern both the local integration scheme of the constitutive equations and the global resolution strategies. In this study, the majority of efforts are devoted to the theoretical developing of damage model. In addition, the models are implemented in computing software MATLAB and CEA CAST3M finite element code, and some calculations are presented to further explain the models in the end of the article.

Residual stresses originate from the elastic accommodation of misfits between different regions in a structure. The interaction between the misfit and the restraint of the surrounding structure determines the magnitude of the resultant residual stress and its length-scale. This paper defines the residual stress length-scales that must be considered in engineering fracture mechanics analyses for welded joints by identifying the crack length-scale of concern. This information is used to estimate measurement length-scale requirements to quantify the stress field and the length-scale that must be represented in finite element weld residual stress simulations.

The effect of residual stresses generated by load history on fracture has been investigated through experimental and numerical studies. In this paper the application of a “local approach” to determine the change in applied load to cause fracture is described. Then the R6 defect assessment procedure is presented. The effect of tensile residual stress on brittle fracture of ferritic steel type A533B at -150ºC is explored. The modified J-integral, J has been also used to estimate the combined crack driving force during loading to fracture of the specimens containing tensile residual stresses ahead of a crack/notch. It is shown that by having more accurate estimates of driving force created by the residual stresses leads to increased agreement between experiments and assessment.

It is well known that mechanical surface treatments such as shot peening can significantly improve the fatigue behavior of highly stressed metallic components. This increase in fatigue and corrosion performance occurs because of the thin layer of residual stresses created by the shot peening process. Literature [1, 2 & 3] is replete with information on the increase in fatigue life with peening but there is little information in open literature on the crack initiation and growth in the shot peened materials. The measurement of fatigue crack growth through this layer of compressive stress field which is less than 0.01” (∼ 0.6mm) thick is a challenge. The present study highlights the attempts to detect crack initiation and measure crack growth in the heavily deformed surface layers, using several measurement techniques of the following aluminum alloys: 7050-T7451 & 7075-T7351. To produce specimens with short cracks several specimen geometries proposed by Suresh & Ritchie [3] were prospected and after several tests it was found that the hourglass coupon with a scratch, the Eccentrically Loaded Single Edge Notched Coupons ESE(T) coupons and the double edge notch coupons DENT(T) similar to the one used by Everett et al [4] would be most appropriate. Several measurement techniques were used in order to detect crack initiation in the hourglass coupons. It was found that the ACPD and eddy current methods were more reliable than the non-contact surface measurement techniques used. The ESE(T) coupons were used to determine the effects of shot peening on crack growth rates, and the results indicate that the effects of peening did not sufficiently retard crack growth for the specimen geometry chosen. Currently work is being conducted to fabricate specimens such that the initial crack is fully embedded in a zone of compressive stresses using the DENT(T) specimen geometry. Understanding the influence of compressive residual stresses and how it affects the fracture mode is central to any investigation on how it may be utilized to improve fatigue resistance of the material. Thus, quantifying and measurement of the residual stress field was also conducted to help better understand its influence on crack growth.

In this study various approaches were applied to bellows to confirm the effect on improving the fatigue strength as follows. As for the effect of the grain size, the re-crystallized materials after cold working are employed. The effect of high strength is studied by using the SUS631 stainless steel so called precipitation hardened semi-austenitic stainless steel. The shot peening process used with reflection plate is also studied to see the effect of residual stress on fatigue strength.

This paper is based on the study of a post mortem analysis of shape memory alloy (SMA) actuators undergoing thermally induced martensitic phase transformation fatigue under various stress levels. Fatigue life results were obtained for both complete and partial phase transformation cycles applied to the SMA actuators. The thermal cyclic loading was induced by forced fluid convection cooling in order to increase the cycling frequency to approximately 1Hz, resulting to corrosion assisted fatigue. The combination of corrosion and reversible phase transformation under stress led to the formation of circular cracks on the surface of the cylindrical SMA wire actuators, which eventually saturated in a periodical distribution. In order to understand the stress field contributions to the microcracking in the presence of eigenstrains, a shear lag model was developed. The model accounts for eigenstrains introduced by corrosion, plastic strain accumulation with the number of cycles and the cyclic phase transformation strain. Comparison of the model predictions with crack spacing reached at fatigue failure is carried out and the reduction of fatigue life of SMA actuators under a corrosive environment is discussed.

Residual stresses can provide a significant contribution to the crack driving force for defects associated with non stress-relieved welds. Structural integrity assessment methods are available which provide detailed guidance for the assessment of such defects under the combined influence of primary and residual stresses. However, in some circumstances these methods may be unduly conservative due, in part, to an over-estimation of the crack driving force contribution from the residual stress, K. This paper describes a programme of experimental and supporting analytical work undertaken to better characterise the influence of residual stress levels on K for cracks in a high strength, low toughness aluminium alloy. The work is based on a compact specimen in which a highly tensile residual stress field is mechanically induced through a compressive preload prior to fatigue pre-cracking. Different approaches to numerically simulate crack development within the residual stress field are explored by finite element analysis and, where possible, numerical data are compared with experimental measurements of crack opening displacement for different crack lengths. The results demonstrate that crack insertion in finite element models provides a than crack insertion. In addition, progressive crack insertion leads to maximum values K which are approximately 30% below those derived using the instantaneous method. The implications of these results for structural integrity assessments are discussed.