An approach is presented that enables the calculation of elastic strain energy in linear and nonlinear elastic solids during arbitrary thermomechanical load cycles. The approach uses the simple fact that the variation of both strain and complementary energies always forms a rectangular shape in stress-strain space, hence integration is no longer required to calculate the energy. Furthermore, the approach considers the mean stress effect so that predictions of fatigue damage are more realistically representative of real-life experimental observations. By doing so, a parameter has been proposed to adjust the mean stress effect. This parameter [Alpha] is based on the well-known Smith-Watson-Topper energy criterion, but allows consideration of other arbitrary mean stress effects, e.g. the Bergmann type criterion. The approach has then been incorporated into a numerical method which can be applied to uniaxial and multiaxial, proportional and non-proportional loadings to predict fatigue damage. The end result of the method is the cyclic evolution of accumulated damage. Numerical examples show how the method presented in this paper could be applied to a nonlinear elastic material
COBISS.SI-ID: 14715163
The existing modified Locati step-test was improved by pairing it with two evolutionary algorithms that were used to minimize the newly defined cost function that measures the deviation of the "best-fit point" trace from the selected target number of load cycles. The main advantage of the new procedure over the conventional Locati step-test is that the slopes and intercepts of the materialʼs or the componentʼs S-N curves do not need to be known in advance in order to estimate the fatigue strength at a selected number of load cycles. The presented procedure was tested on two cases with a different target number of load cycles. The results indicate that the presented procedure is adequate to the conventional Locati step-test procedure.
COBISS.SI-ID: 13999387
The physical and mechanical properties of beech wood (Fagus sylvatica L.) were determined after industrial thermal treatment in a steam atmosphere. Parallel clear uniaxial compression specimens (20 × 20 × 20 mm) were made from control and thermally treated wood, conditioned in a series from an oven dry to saturated atmosphere (20 °C) and compression loaded parallel and transverse to the grain. The reduced density of thermally treated beech was reflected in the decreased stiffness and, especially, strength of wood transverse to the grain. No impact of thermal treatment on the longitudinal compression strength of wood was confirmed. Lower hygroscopicity was additionally detected with thermo-modified wood, whereas the relationship between wood moisture content and stiffness (MOE/MOE0), as well as strength (σ/σ0), along and transverse to the grain of the beech wood remained identical.
COBISS.SI-ID: 2519945
To reduce R&D cost the products behaviour i n exploitation is predicted using numerical simulations in early R&D phases. If a structure is subjected to a high - strain rate loading this effect should be considered in the material models that are used for numerical simulations. This article shows how t he strain - rate dependent material parameters can be determined by combining the experimental data with the numerical simulations. The presented methodology is based on an application of Taguchi arrays for finding the most adequate values for the strain - rat e dependent parameters. The presented methodology is applied on the practical case, for which the parameters of the Cowper - Symonds and Johnson - Cook material models are estimated.
COBISS.SI-ID: 14571547
Reliable durability predictions are the key to safe products, lightweight constructions and low production costs. Due to the many influences on durability predictions, such as variable mechanical loads, changeable temperatures and corrosive environments, an engineering tool that enables the consideration of a range of influences and ensures reliable prediction is a necessity in industry today. The aim of this project was to predict the thermomechanical fatigue damage for three components of an exhaust system. The objective of the research from Siemens and the University of Ljubljana was a correlation between predicted and experimentally observed critical locations and their durability.
COBISS.SI-ID: 14500891