Thermal Elastic-Plastic Analysis Considering Temperature Rise by Rapid Plastic Deformation in Undermatched Joints

The characteristics of dynamic strength and fracture in structural steels and their welded joints particularly for pipelines should be evaluated based on the effects of the strain rate and service temperature. The temperature, however, rises so rapidly in structures due to the plastic work under the high strain rate such as ground sliding by earthquake when the effect of the temperature cannot be negligible for the dynamic fracture. It is difficult to predict or measure the temperature rise history with the corresponding stress-strain behavior, including the region beyond the uniform elongation, though the behavior at the large strain region after the maximum loading point is very important for the evaluation of fracture. In this paper, the coupling phenomena of the temperature and stress-strain fields under dynamic loading were simulated by using the finite element method. A modified rate-temperature parameter was defined by accounting for the effect of the temperature rise under rapid plastic deformation, and it was applied to the fully coupled analysis between the heat conduction and thermal elastic-plastic behavior. The temperature rise and stress-strain behavior, including the coupling phenomena, were studied including the region beyond the maximum loading point in structural steels and their undermatched joints, and then compared with the measured values.

Effect of Plastic Constraint and Strain Rate on Characteristics of Strength and Fracture in Undermatched Joints

Welded joint generally has heterogeneity of strength, material, and fracture toughness. It is important to understand the characteristics of material strength and fracture in welded joint considering plastic constraint effect due to material heterogeneity. Furthermore, the material behavior becomes more complicated when welded joint receives dynamic loading like as earthquake. In this paper, the characteristics of strength and fracture in undermatched joints with strength heterogeneity under dynamic loading were studied by round-bar tension tests and thermal elastic-plastic analysis. These strength and fracture in undermatched joints are evaluated by considering the effects of strain rate and temperature including temperature rise due to rapid plastic deformation. The differences of fracture characteristics such as ductile-to-brittle transition behavior are considered from the plastic constraint effect and strain rate effect, and they are precisely explained in terms of the stress-strain distribution obtained by numerical analysis.

A Finite Element Study of Electromagnetic Riveting

Electromagnetic riveting, used in some aerospace assembly processes, involves rapid deformation, leading to the finished rivet configuration. Analysis of this process is described for the case of an aluminum rivet joining typical aluminum structural elements. The analysis is based on a finite element method that includes the effects of heating, due to rapid plastic deformation of the material, on the material properties. Useful details of material deformation and thermal history and the final rivet and structure configuration and states of stress and strain are obtained. These results have significant implications in the design, implementation, and improvement of practical fastening processes in the aerospace industry.

New orientation relationship in martensitic transformation in austenitic stainless steel welded explosively

Martensitic transformation induced by plastic deformation in 18/8 stainless steel has been extensively investigated by many workers. Venablel has proposed that the orientation relationships in transformations are (111)γ// (00.1)ε// (011)α and [101]γ//[11.0]ε//[lll]α. Since metals welded explosively or shock loaded are subjected to rapid plastic deformation under a high pressure, the aspects of martensitic transformations are expected to be different from those reported hitherto. The purpose of the present experiment is to show the new orientation relationship in transformation and the new aspects of transformations in 18/8 stainless steel welded explosively as well as shock loaded. The atomic movements required in transformation are also considered.Austenitic stainless steel plates, 3×50×200 mm, were heated in vacuum at about 700°C for 30 min to transform existing ε and α phases into γ phase. They were welded explosively by using two kinds of explosives with detonation velocities of 2,400 m/s and 5,000 m/s.