Optimization Design of a Small-Sized Cruciform Specimen for Biaxial Fatigue Testing

The in-plane biaxial specimen can well reflect the complex stress state of sheet metal. However, there is no standard for small-sized specimens used in the low-power biaxial fatigue testing machine. The main goal of this paper is to apply the finite element method and orthogonal experiment method to design the cruciform specimen, considering the influence of three main parameters including the diameter of the central semispherical thinning area, the minimum thickness of the center and the arm thickness of the specimen. According to the central strain dispersion coefficient and the strain concentration coefficient proposed in this paper, we ensured that the distribution of strain in the gauge area is uniform and the strain it at its maximum value at the same time. The optimized specimen is verified by a biaxial fatigue test with the digital image correlation (DIC) technique. It is found that the fatigue crack appears in the center region, which proves that the optimized specimen can be effectively used for biaxial fatigue test.

Numerical Modelling of the Biaxial Fatigue Test of Aluminium Wheels

The paper is devoted to the numerical simulation of fatigue life of lightweight aluminium wheels subject to biaxial fatigue test. A numerical model based on finite elements is developed for the scope. The model receives as input the test load sequences and outputs the fatigue life of wheel. Two different methods for modelling the load transfer mechanism of the tyre have been analysed, i.e. how the tyre-drum contact forces are transferred to the wheel rim. The first method consists of a simple cosine loading function acting on a fixed arch of the wheel rim. The second method relies on a physical model of the tyre that is fixed at the tyre-rim interface surface; the computed reaction forces are fed as input to the wheel model. The fatigue life of the wheel is estimated by using the Palmgrem-Miner approach. Both the Sines fatigue criterion and the Papadopoulos critical plane with gradient effect criterion are used and the results are compared. Experimental tests have been performed on an actual wheel mounted on the biaxial test bench for a preliminary validation of the method.

INCEFA-PLUS Project: Review of the Test Programme

The European Project INCEFA-PLUS (INcreasing Safety in NPPs by Covering gaps in Environmental Fatigue Assessment) characterizes environmentally assisted fatigue of stainless steels in light water reactor environments. The project includes a major test programme during which more than 200 fatigue tests have been carried out in different laboratories across Europe. The test campaign was structured in three successive phases with slightly different foci. All testing programmes were optimized by means of the Design of Experiment method. The majority of the tests were carried out on a single batch of 304L which were complemented by tests on different batches of 304L and on X6 CrNiTi 18 10, a Ti stabilized steel used in VVERs. The influences of mean strain, surface roughness and hold time on fatigue life in air and water environment at a given environmental fatigue correction factor Fen were investigated. Besides the main test campaign, additional activities on the effects of mean stress, testing at reduced Fen, and different applications of hold time as well as biaxial fatigue tests have been carried out. The paper is part of a special session for the dissemination of the project results. It summarizes the tests performed during the project and provides the basis for the project conclusions in a different paper in the same session.