Radek Kottner

Modeling of material damage using finite elements and time homogenization in case of finite strain

This work is aimed at numerical simulations of high-cycle fatigue behavior of elastomeric materials. The main concern, however, is not the fatigue life itself, but the changes of mechanical properties prior to failure. This is of special interest in the case of elastomers. In such a case, large strains must be considered and so does, consequently, nonlinearity of constitutive equations as well. The usual approach to fatigue analysis consists of modal analysis and application of linear cumulation rule for damage. This is not generally applicable to large-strain regime nor to nonlinear material models. The most general approach to such problem is a full simulation of damage cumulation in time domain. Such a simulation, however, would be prohibitively expensive for a large number of loading cycles. As a remedy, the method of homogenization in time domain may be applied to the problem. The method has been applied to various material models already (viscoelasticity, viscoplasticity, damage). This article shows its applicability to the problem of damage cumulation under large strains and a significant improvement in computational times over full simulation.

Strength Determination of Composite Flexible Joint

This thesis deals with the design of a joint for composite flexible elements using an integrated connection. For the verification of the selected layout, a wrapping loop was chosen as a simplified member, which was created on a special form designed for these samples. The material used was unidirectional fibreglass and epoxy resin. These samples were then compared using quasi-static tensile and compression tests. The tests were carried out with the Zwick-Roell Z050 machine. The resulting data of the experiment were then compared with the data obtained from numerical simulations using the finite element system Siemens NX 10 and SIMULIA Abaqus 6.13. 3D strength criteria Maximum stress and direct-mode strength criterion LaRC04 were used for evaluation.

Experimental and Numerical Investigation of Critical Buckle Load of Composite Specimens

Different carbon and glass fibre strips were subjected to the double clamp buckle beam test. Furthermore, thin-walled glass fibre box-beams were subjected to the three-point bending test. Results of experiments were compared to different numerical simulations using buckling analysis or static analysis considering large deformations.

Investigation of Long-Term Mechanical Response of Rubber

This work deals with mechanical properties of rubber that is used as a damping element in modern tram wheels. Tests in simple tension, uniaxial compression, and simple shear were performed. Duration of the experiments varied from minutes to days in order to investigate permanent set and its dependence on previous loading history, especially maximum strain. Apart from measurements using the testing machine, hydraulic vise was used for measuring force at constant strain and an optical distance-measuring system was used for measuring the dimension of specimens in the loading direction after load removal. The aim of the research was to find out whether the final dimensions of specimens are the same as before loading and whether the force after return to zero strain attains zero. This knowledge is essential for reliability analysis of the resilient wheels that use the examined rubber.

Failure Analysis of Pin Joint of Carbon/Epoxy Composite Plate

This paper deals with the failure analysis of a carbon fibre reinforced plastic (CFRP) plate which is joined to a structure using a steel pin. The analysis was carried out experimentally and numerically using the finite element method (FEM) system MSC.Marc. The Puck´s failure criterion for 3D stress state was used after its implementation into the MSC.Marc system. Experimental specimens were symmetrical laminates with 8 layers. A special experimental device which allowed monitoring of all visible changes of the experimental specimens with cameras was designed. This device was installed into the testing machine Zwick/Roell Z050. Obtained images were evaluated using the digital image correlation technique. Moreover, the vibrations in the surroundings of the specimens were measured to detect acoustic emissions which occur during damage.

Strength Analysis of Carbon Fiber-reinforced Plastic Coupling for Tensile and Compressive Loading Transmission

The design and production of high strength composite/metal joint is generally a challenging task. This work focuses on joints that can be produced using filament winding technology. The main principle in this case is that the fibers of the composite are wrapped directly around the shape of a metal component, for example a pin. It allows the creation of a joint, where the load is transferred directly from the metal part into the composite structure without cutting fibers. Therefore, high performance in strength can be achieved. The composite part of the joint can also constitute flexible coupling between two metal components. The investigation of mechanical behavior of a carbon fiber-reinforced plastic coupling under tension, compression, and bending is carried out. Performed experiments are compared with three-dimensional finite element simulations where adjusted LaRC04 failure criterion is used. The influence of the coupling concept and its geometry on the joint strength is investigated.