An integrated fracture mechanics approach is proposed to account for the estimation of the fatigue resistance of component. Applications, estimations and results showed very good agreements with experimental results. The model is simple to apply, accounts for the main geometrical, mechanical and material parameters that define the fatigue resistance, and allows accurate predictions. It offers a change in design philosophy: It could be used for design, while simultaneously dealing with crack propagation thresholds. Furthermore, it allows quantification of the material defect sensitivity. In the case of the set of fatigue tests carried out by rotational bending of specimens without residual stresses, the estimated results showed good agreement and that an initial crack length of 0.5 mm can conservatively explain experimental data. In the case of fatigue tests carried out on the springs at their final condition with bending at R = 0.1 our data shows the influence of compressive residual stresses on fatigue strength. Results also showed that the procedures allow us to analyze the different combinations of initial crack length and residual stress levels, and how much the fatigue resistance can change by changing that configuration. For this set of tests, the fatigue resistance estimated for an initial crack length equal to 0.35 mm, can explain all testing data observed for the springs.
B.04 Guest lecture
COBISS.SI-ID: 19104790The recent performed on-line monitoring of strain in pillar’s legs of transmission line shows correlation between weather conditions, temperature of air and temperature of conductor vs. length of conductor, sag and change of tensile force in conductor. The new study has been suggested by Slovenian operator for high voltage electrical energy provider. The study is dealing with change of deformation in legs of pillars. The boundary conditions are obtained by experimental measurement of strain in legs and geometrical measurement of all three conductors between two pillars. The performed study shows that online monitoring of change strain can be connected with change of geometry of conductors and consequently the change of tensile force in conductor. The change of tensile force in conductor can be caused by additional weight or temperature change. The verification of model requires additional measurement of conductors geometry at least three different temperature including parallel measurement of strain in legs.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 18736406Components 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. Fatigue induced flaw growth was monitored on a 4-point specimen, loaded by cyclic dynamic bend forces. The flaw growth was monitored by strain gauges with standard resistance of 120Ω. After performance of fractal-graphical measurements, a flaw growth analysis was performed to determine the shape, propagation and cross sections of the crack. To determine the stress intensity factor a numerical model was developed based on measured crack shapes, material properties and cyclic loading data of the actual tested specimen. The investigation results showed that derived calibration curve could be used to predict surface deformations as a result of crack propagation and growth, but not crack initiation. With the determination of surface deformation, one could follow the crack transition from semielliptical surface crack to through thickness crack. Stress intensity factor has been determined numerically by using Finite element method for five different fatigue crack fronts. Results show that fatigue crack on the surface of specimen propagated under almost same stress intensity factor value. Consequently, in our case, the fatigue crack growth rate was constant during transition from surface semi-elliptical crack to through thickness crack front. The goal of this paper is to describe methodology and results based on experimental and numerical modeling during crack propagation and potential use of this technique for online monitoring purposes.
B.04 Guest lecture
COBISS.SI-ID: 18798358This paper discusses modern FEA-driven simulation procedures used in design of structural load-carrying parts. The focus of the paper is on topology optimization usage within the context of two currently very interesting topics: configuration and optimization of lattice structures and modern additive manufacturing technologies. The discussion is enriched by numerical examples and experimentally obtained results.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 18962454Fracture toughness Measurement of thin walled pipe-line with flaw or defect in most critical axial direction is difficult. In this paper the non-standard modified specimens has been proposed for simple fracture testing. The comparison between fracture behaviour of single edge notch bending (SENB), compact tension (CT) and pipe-ring specimens with notch and fatigue pre-crack were analysed. In order to determine CTOD-R curve the normalization method by using remote measurement CMOD has been used for all specimens. For non-standard pipe ring pre-cracked specimens the plastic correction eta factor is determined by using finite element method. The stable crack growth initiation was determined also as a crack tip surface strain-relaxation by using stereo-optical grading method. Comparison between CTOD-R curves of all three types of specimens shows quite similar fracture toughness in stable crack initiation range.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 17933078