This paper deals with experimental investigations and numerical simulations of HELICOIL® inserts in ABS-M30 plastic. The aim is to explore the possibilities of modelling HELICOIL® inserts using Finite Element Method (FEM) and thus predict the load-bearing capacity of these inserts. The motivation was based on a previously published article that dealt with the topological design of the robot manipulator arm shape. During the mechanical tests, the structure of the arm did not collapse, but the HELICOIL® inserts were torn out. To determine the load-bearing capacity of HELICOIL® inserts, the necessary experimental tests were designed and carried out. FEM calculations of the inserts were adjusted to the obtained data. The results from the FEM were verified in an experimental validation test.

Abstract:The conventional method for evaluation of the fatigue constants uses one set of experimental data from strain-controlled uniaxial fatigue tests. However, these constants do not ensure the compatibility conditions. The new 3D method retains the mathematical and physical relationships between curves considered. This paper presents a way of implementation of the identification procedure and shows results obtained for three types of materials. KEYWORDS:Fatigue constant, low-cycle fatigue, 3D method. IntroductionNowadays, fatigue behaviour of materials is described mostly by the stress-strain curve in the form of Ramberg-Osgood equation and by the Manson-Coffin-Basquin equation in the form of the strain-life curve. It is well known that the assumption of equality of the plastic and elastic components in both equations leads to the so called compatibility condition. The conventional evaluation method of fatigue constants uses one set of experimental data from strain-controlled uniaxial fatigue tests. However, these constants do not ensure the compatibility conditions. A new method proposed by A. Nieslony [1] for determining the stress-strain and strain-life curves retains the mathematical and physical relationships between the curves considered. This paper presents a way of implementation of the identification procedure and shows some interesting results obtained for three types of materials: aluminum alloy 2124T851, stainless steel 316L and structural steel ST52. Identification of fatigue constantFor evaluation of low cycle fatigue tension-compression tests, the Manson-CoffinBasquin equation [2] is applied usually. It illustrates the relationship between the amplitude of total strain and number of cycles to crack initiationwhere -amplitude of elastic strain, -amplitude of plastic strain, , -fatigue ductility coefficient, c -fatigue ductility exponent, , -fatigue strength coefficient, b -fatigue strength exponent.

This paper examines the effect of experiments used to identify material parameters of a more complex material model (12 material parameters). The set of experiments includes tensile tests and indentation tests with different loading conditions at 4 different temperatures (a total of 14 experiments) for the ABS-M30 material. The behaviour of the material was simulated using Anand's material model, and the Finite Element Model Updating approach was used to identify the material parameters. The parameters are solved for 3 variants: identification from indentation tests, identification from tensile tests, identification from all experiments. For the first two variants, the remaining experiments are used to verify. Finally, all results are compared.

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An evolutionary procedure for multiple materials is presented. A material is selected due to an allowable stress interval for the material. The presented method includes a mesh-independent filter. The proposed algorithm is applied to three examples with four or five materials. In the presented examples, the effect of an evolution rate, a filter setting, and the number of elements, are shown in a simplified way. It is shown that the final topology of structure meets the stress requirements of the materials.