Residual stresses could be induced by the plastic torsion loading of a solid round bar. This article deals with the residual stresses generated at the surface during the process of plastic pre-setting. Residual stresses were measured on the surface of a specimen by x-ray diffraction for different angles of subsequent plastic pre-setting. In addition, the residual stresses were calculated using analytical and numerical modelling by Finite element methods. The analytical approach was based on the torsional characteristic, T-y, of the material and tension test results. It has been found that the direction of cold rolling on the surface has a significant influence on residual stresses, as it is reflected in the initial stress state. A good agreement between analytical modelling, finite element analysis, and experimental residual stress measurement was obtained.
COBISS.SI-ID: 18360086
Retardation of fatigue crack growth rate due to the introduction of thin, compliant and/or soft interlayers is investigated. The mechanism is the reduction of the crack driving force in the interlayer. Fatigue tests are conducted on composites made of high-strength aluminum alloy as matrix and technically pure aluminum or adhesive as interlayer material. The adhesive interlayer causes an increase in fatigue life by a factor 20 or more, whereas the aluminum interlayer yields only a moderate improvement. Numerical simulations based on the configurational force concept are utilized for understanding. The results show new possibilities for the design of fatigue-resistant materials
COBISS.SI-ID: 19101206
A material with spatial variation in the elastic modulus E can have a much higher apparent fracture resistance and fracture stress than a comparable homogeneous material. The effect occurs due to the strong decrease of the crack driving force, which leads to crack arrest when the crack tip is located in the region with low elastic modulus. From the results of exemplary numerical studies and simple fracture mechanical considerations, models are derived in order to predict the fracture stress and fracture toughness of the inhomogeneous materials. It is shown that high values of fracture stress and fracture toughness can be reached if the amplitude of the E variation is high enough to provide crack arrest and the wavelength of the E variation is small. The beneficial effect of material property variations also occurs if the width of the compliant region is very thin and the loss in stiffness of the structure is almost negligible. The concept is applicable for various types of composite materials; examples are presented.
COBISS.SI-ID: 17637910
This paper presents an approach to shape/topology optimization of continuous structures. The proposed approach combines the design element technique and the level set function in order to obtain an efficient topology parameterization of the domain under consideration. The shape and the level set function are both parameterized by the control points and corresponding blending functions of the design elements. For the sake of generality, nonlinear finite elements are employed, which have to be adapted adequately in order to be able to describe full material, void, and any intermediate state. In this way the design element technique has not yet been used for topology optimization, partially because it requires that the domain geometry and finite element mesh have to be defined by utilizing control-point-based design elements. In spite of this drawback, the proposed approach offers several attractive benefits. Namely, in contrast to other level set methods, the proposed approach does not make any use of the Hamilton-Jacobi differential equation. Consequently, the boundary evolution stage of the process need not to be treated separately, but is integrated with the strain/stress analysis stage into a rather conventional optimization scheme. Furthermore, the proposed approach allows for any type of finite elements (linear/nonlinear) to be implemented into the procedure if adjusted adequately. The formulation of the optimization problem is also completely arbitrary. The properties of the proposed approach are illustrated by several numerical examples.
COBISS.SI-ID: 17160982
This paper presents on approach for determining the plastic load line displacement (ηpl LLD) and the plastic crack mouth opening displacement (ηpl CMOD) correction factors for Pipe – Ring Notched Bend (PRNB) specimens, in order to estimate the J-integral and analyze the elasticplastic behavior of tested pipeline materials. The evaluation of the ηpl factors is based on the load separation method. Finite Element Method is employed for estimating the separation parameters. The notch tip radius of blunt notched specimens varies within an interval Rn = 0; 0.1; 0.25; 0.5; 0.75; 1.25; 1.5 and 2mm. The effect of the notch tip radius on the ηpl factors is analyzed.
COBISS.SI-ID: 17623830