Structural integrity assessment of pipeline requires limit load solutions for variety of crack depth in order to predict loading capacity of pipeline or resistance to initiation and crack growth. Standard fracture toughness testing of thin walled pipeline is often difficult to perform in order to complete standard requirements. In order to find alternative technique for measurement fracture toughness of already delivered pipeline segment, the new pipe–ring specimen has been proposed. In order to determine normalized fracture toughness of pipe-ring specimens the limit load is necessary to determine. The limit load is dependent on geometry of specimen and loading manner. It is assumed that ligament at the deepest point of crack is fully yielded. The ligament yielding of pipe-ring specimens containing through thickness axial crack under combined loads is going to be calculated by the finite element method. Paper provides limit load solutions for pipe-ring containing two diametric symmetrical cracks with same depth ratio in range of 0.45≤a/W≤0.55. To validate the proposed limit load expressions, the results of finite elements analyses are compared with experimental results.
COBISS.SI-ID: 17203990
The standards for characterization of fracture toughness of metals are focused on the calculation of fracture parameters based only on in-plane displacements of the specimen tested. Although fracture is a three-dimensionalproblem, out-of-plane displacements of the specimen tested are not mentioned in those documents. Since three-dimensional displacement measurement is available, it is worth investigating its potential uses in fracture tests. In this work, the fracture toughness of a structural steel was assessed through standard tests, measuring three-dimensional surface displacements. An alternative Crack Tip Opening Displacement calculation was introduced. The fracture initiation was inferred from the out-of-plane displacements, finding good agreement with results from R-curves.
COBISS.SI-ID: 16553750
The Stress-Intensity Factor for the circumferential semi-elliptical surface cracks in a hollow cylinderćs cross section under torsion is calculated using a finite-element technique. The configuration of the semi ellipse follows the standard notation of the outer surface crack-lengths and the crack depths. The compendia for the Stress-Intensity Factor solutions for Mode II, Mode III and both mixed modes are given for the broader aspect ratios and relative crack-depths than previously available. The magnitude of the Stress-Intensity Factor of Mode II near the free surface becomes more significant for stable crack-initiation than that of Mode III at any point along semi-elliptical crack.
COBISS.SI-ID: 16841238
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
Components and structures exposed to elastic dynamic loading respond with elastic strains on the surface of the material. Mechanical response could be monitored by deformations on the surface. The measurements and monitoring of these parameters could be performed with electronic devices for on-line measurements, controlled by computerized systems. In the case of fatigue crack initiation and propagation the cyclic strain amplitude deviated from initial strain response (mean value and amplitude). Implementation of appropriate monitoring system supported by computerized programs for evaluation, analyses and activation represent important means to safe service component or construction. To evaluate flaw depth growth, the strain gauge measuring sensors could be used. These sensors measure surface deformation relaxation due to flaw depth growth. The monitoring of the material under cyclic loading could be performed with experimentally determined calibration curve, representing deformation on the surface and depth of the semi-elliptical crack growth on the surface or cross section of the material. The goal of this paper is describe electronic device and experimental procedure in order to determine calibration function.
COBISS.SI-ID: 16794390