Fatigue tests and estimation of crack initiation and propagation lives in AISI 304L butt-welds with reinforcement intact

Abstract: Welding is one of the most common methods in industrial practice for joining components. Its main advantages are high speed in manufacturing combined with low costs and, usually, a high degree of flexibility, integrity and reliability. Nevertheless, welding is a highly complex metallurgical process and, therefore, weldments are susceptible to material discontinuities, flaws and residual stresses which may lead to structural failure and life time reduction. As a consequence weldments are an important field of fracture mechanics methods although its application is more complex than for homogeneous or non-welded structures. The aim of the paper is to provide an overview on the current state of fracture mechanics application to weldments. It starts by discussing the specific features which any fracture mechanics analysis of weldments has to take into account. Then, the experimental determination of fracture toughness, fatigue crack propagation and tensile properties of weldments is addressed. Finally, the analytical determination of the crack driving force in components and structural integrity assessment approaches for weldments are presented.

Abstract: Abstract AISI 304L is an austenitic Chromium-Nickel stainless steel offering the optimum combination of corrosion resistance, strength, and ductility. These attributes make it a favorite for many mechanical switch components. The low carbon content reduces susceptibility to carbide precipitation during welding. In the present paper a thorough review on welding of AISI 304L austenitic Stainless Steel by various welding processes was made. From the review it is understood that AISI 304L austenitic Stainless Steel is the best material where there is a problem of intergranular corrosion. Also it is one of the best materials frequently used in manufacturing non heat treatable components.

Abstract: Fatigue life of engineering structure contains two parts: crack initiation life and crack propagation life. Fracture mechanics is adopted to estimate crack propagation life in the real engineering structures and has made some achievements. Actually, the existing study indicated that fatigue crack initiation is also an important period in the whole fatigue life. So, a new method to predict the whole fatigue life of notch components is proposed based on the theory of damage mechanics in this paper. The damage evolution equation of notch specimen under tension compression loading is obtained based on closed-form solution. The stress distributions of notch root are analyzed by finite element method. The whole fatigue life of notch specimen is estimated by the proposed method when stress concentration factor is different. It has been verified that the results calculated by proposed method is close to the experimental results and the model put forward in this paper is superior to Manson-Coffin Law. The result indicates that the proposed method is concise, effective and feasible for practical application.

Abstract: It is usually a lot easier and less expensive to galvanize steel before it is welded into useful products. Galvanizing afterwards is almost impossible. In this research work, Galvanized Steel was welded by using the ER 308L stainless steel filler material. This work was done to find out an alternative way of welding and investigate the effects of heat input on the mechanical properties of butt welded joints of Galvanized Steel. A 13.7 kW maximum capacity MIG welding machine was used to join 1.6 mm thick sheet of galvanized steel with V groove and no gap between mm. Heat inputs was gradually increased from 21.06 to 25.07 joules/mm in this study. The result shows almost macro defects free welding and with increasing heat input the ultimate tensile strength and welding efficiency decrease. The Vickers hardness also decreases at HAZ with increasing heat input and for each individual specimen; hardness was lowest in heat affected zone (HAZ), intermediate in base metal and maximum in welded zone. The fracture for all specimens was in the heat affected zone while testing in the universal testing machine.

Abstract: Stainless steel possesses outstanding advantages such as good corrosion resistance and long service life. Stainless steel is one of the primary materials used for sustainable structures, and welding is one of the main connection modes of stainless-steel bridges and other structures. Therefore, fatigue damage at welded joints deserves attention. The existing fatigue design codes of stainless-steel structures mainly adopt the design philosophy of structural steel. In order to comprehensively review the published fatigue test data of welded joints in stainless steel, in this paper, the fatigue test data of representative welded joints of stainless steel were summarized comprehensively and the S–N curves of six representative stainless-steel welded joints were obtained by statistical evaluation. The comparison of the fatigue strength from existing design codes and fatigue test data was performed, and the results showed that the fatigue strength of welded joints of stainless steel was higher than that of structural-steel welded joints. The flexibility of regression analysis with and without a fixed negative inverse slope was discussed based on the scatter index. It was found that the fatigue test data of stainless-steel welded joints are more consistent with the S–N curve regressed by a free negative inverse slope. In this paper, a design proposal for the fatigue strength of representative welded joints of stainless steel is presented based on the S–N curve regressed by the free negative inverse slope.

Abstract: Fatigue design handbook , Fatigue design handbook , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Abstract: In most of the lower fatigue strength welded joints failure occurs by the propagation of a semi-elliptical surface crack which initiates at the weld toe. In order to analyse the progress of these cracks using fracture mechanics techniques, the solution for the stress intensity factor, K, is required. Fatigue cracks in most welded joints adopt shapes which give low a/2c values (up to approximately 0.3) while solutions in the literature are more applicable to a/2c values close to 0.5. Therefore, results in the literature were used to estimate the stress intensity factor for cracks with low a/2c values. Furthermore, the effect of the weld stress concentration factor was incorporated in the solution. The accuracy of the resulting solution was confirmed by using it to determine ΔK values of weld toe cracks for which crack propagation data were available. The results agreed with the expected da/dN vs. ΔK scatterband obtained from centre-notched specimens.