We present an alternative approach to the rapid estimation of S-N curves and their scatter. A simultaneous estimation of the SN curve and its scatter is achieved by applying a two-parametric Weibull distribution to describe the scatter of a number of load cycles to failure at an arbitrary amplitude stress level. The shape of the S-N curve is generally modelled as a linear dependence between the logarithmic value of the number of load cycles to failure and the logarithmic value of the amplitude stress level. This dependence is described by two parameters: a constant term and a scale coefficient of the S-N curve in a loglog scale. Therefore, the same formulation was applied to model the dependence between a scale parameter of the Weibull distribution and the logarithmic value of the amplitude stress level. In this manner the S-N curve and its scatter are described by three parameters: the constant term, the scale coefficient and the shape parameter of the Weibull distribution. The three parameters are estimated with a differential ant-stigmergy algorithm from the experimental data. In the article a mathematical background of the approach is presented and applied to three cases of experimentally obtained durability data. The results are analysed and discussed.
COBISS.SI-ID: 12242203
Church bells are exposed to severe loading conditions during ringing, which results in different damage modes due to material wear, fatigue loading, material deficiencies, different clapper-to-bell layouts, etc. As part of the activities of an EU-funded project called Maintenance and Protection of Bells (PROBELL), experimental investigations and finite-element simulations of the local contact between the clapper and the bell were carried out to study the wear-related damage to bells. First a simplified model was built to assess under the laboratory-controlled conditions the consequences of the repetitive impacts between a spherical body made from steel and a flat block made from bronze. After the results of the finiteelement simulations for a simplified model were in reasonable agreement with the measured data a full-scale finite-element model for simulating the repetitive clapper-to-bell strokes was built. The simulations with the full-scale model were performed for variations of the parameters that influence the structural behaviour of the bell and the clapper: the clapper material, the clapper mass, the relative impact velocity of the clapper, the shape of the clapper, the clappers pin support, the clappers impact angle, the clappers guide accuracy, the bells sound-burp thickness and the coefficient of friction between the clapper and the bell. The agreement between the simulated and the measured results and the relation between the local stressestrain state and the damage to the bell in the contact area are discussed.
COBISS.SI-ID: 12166171
The paper presents a numerical approach to compute the total amount of dissipated energy under arbitrary rate independent uniaxial thermomechanical fatigue (TMF) loading. Such an approach is based on the stress controlled Prandtl type operator enabling continuous energy dissipation calculation. It focuses on non-isothermal stress-strain conditions of a spring-slider segment, and relates slider movements to irreversible energy dissipation. The correct amount of dissipated energy is computed at any moment (online), without the need of "waiting" the cycle to finish. The operator approach guaranties monotonically increasing progress of energy dissipation, which is within the framework of thermodynamics. It is also shown that the operator approach results in the same dissipated energy after closed isothermal cycle as the traditional integration approach.
COBISS.SI-ID: 12269595
The article focuses on the application of a recently developed damage operator-based lifetime calculation to a thermomechanically loaded exhaust downpipe. The damage operator approach enabling online continuous damage calculations for isothermal and non-isothermal loading with mean stress corrections is reviewed. The article also highlights an extension of the strain-life approach to take into account viscoplastic effects and creep. The transient results from thermal and structural analyses using finite element analyses have been applied to the exhaust downpipe in LMS Virtual.Lab and the damage predicted. Tested exhaust downpipes were then subjected to the same loading conditions as in the calculation, and load cycles were repeated up to the point of failure. Simulated and test results are comparable.
COBISS.SI-ID: 11851547
In the present study, the conditions of chip propagation or fracture in orthogonal oblique cutting of beech wood (Fagus silvatica) in the 90° direction for a type-I chip has been investigated. The force required for orthogonal wood cutting is pronouncedly variable, which is the consequence of exchangeable different ways of material breakdown. The chip formation process is discontinuous because of interrupted splitting of the material in front of the cutting tool. A 10-mm-thick specimen was cut at a rake angle of 31° and 42° with chip thicknesses ranging from 0.1 to 0.3 mm. The chip segment length increased with the chip thickness. A chip of varying length and thickness was modelled using the finite element method. For each case, the bending or compressive stress in the chip and the stress intensity factor at the crack tip was calculated. The segment length of the chip can be calculated by taking into account the condition that a crack propagates when the stress intensity factor K I at the crack tip equals the critical stress intensity factor K IC, and the bending or compressive stress sigma x in the chip is smaller than the strength sigma u. Good agreement between the calculated and the measured values was observed. The chip segment length can change considerably already with small changes in the bending strength and critical stress intensity factor. This large sensitivity is also confirmed by the fluctuation of the measured chip segment lengths by as much as 400%.
COBISS.SI-ID: 1989001