<p>This report is a review of some failure models today used for determine failure in thin sheets of high strength steels. Focus has been given on phenomenlogical models and only some simple simulations have been carried out. The phenomenlogical models that have been summarized here are of four different categories, namely stress based, strain based, combined stress and strain based and damaged models. However, the simulations have only been preformed for some of the models.</p>

This report is a review of some failure models today used for determine failure in thin sheets of high strength steels. Focus has been given on phenomenlogical models and only some simple simulations have been carried out. The phenomenlogical models that have been summarized here are of four different categories, namely stress based, strain based, combined stress and strain based and damaged models. However, the simulations have only been preformed for some of the models.

The master thesis deals with a stress-strain analysis of the front crash structure of a race car by using the finite element method. The structure is loaded by an impact loading. This type of analysis belongs to the transient analysis so the explicit formulation of the finite element method is used. The LS-DYNA software was used for calculations. The goal of this thesis is to express the influence of the crash structure to the change of the car's kinetic energy as well as the amount of absorbed energy in case of frontal impact.

The main subject of this master thesis is the computational modeling of stress-strain analysis of the loaded front part of Toyota Yaris from the year 2010 using an explicit finite element method (FEM). The aim of this thesis is the assessment of resistance of the front part of the car (longeron) at the impact stress. This thesis describes the selection, editing, and creation of the computational model of longeron and simulation of the barrier collision. The objective of the thesis is to use a real vehicle, suggest modified longerons to be implemented in it, test various shape and material versions of the longeron and make their comparison.

In 1995 was published a regulation from RCAR company which determines rules for crash tests in maximum speed of 15 km/h on vehicles lighter than 2,5 ton. The main reason was to reduce costs for car reparation in case of crash in low speed. My diploma thesis is focused on the modifications of deformation part in the car alias absorption part of the vehicle. In the first part of my diploma thesis has been done a research about organisations doing basic car crashes as well as topic focused on nonlinear mechanics and description of explicit FEM. In the second part of my work are settled conditions for crash simulation of a barrier into the car. There is an evaluation of critical force on the stringer. Afterwards the calculating simulation simplified on loading of absorption part and there are some material and form adjustments. In the final part of my diploma thesis is done a result comparison and development of the absorption part.

Blades used on brushcutters and lawn mowers are subjected to a wide variety of working conditions. Besides continuous loads from cutting grass, the blades are also subjected to accidental impacts of branches, stones and structures. Due to exceptionally high rotational velocities, these types of impacts involve blade deformation at high strain rates. This master’s thesis aims to improve understanding and predictability of blade properties for design of future blades. The project is aimed at characterization of the mechanical response of steel used for brushcutter blades and developing a simulation model of a blade impact load case. Thus, the problem was divided into two main parts: firstly, material characterization, and secondly, numerical modeling. The objective of the material characterization part was to determine the rate dependence of the flow stress for two hardened steels. Experimental compression tests were performed at quasi-static strain rates (10-4 - 10-2 s-1) and at high strain rates (102 - 104 s-1) in order to characterize the rate dependence of each material. The objective of the numerical modeling part was to develop simulation models of an impact load case for the purpose of recreating tests performed with an experimental test setup. The simulation models were aimed to include material models for the blade based on the experimental tests performed for the two hardened steels. In preparation for the compression tests, cylindrical specimens were acquired through electrical discharge machining involving material removal from blades intended for brushcutters. Compression tests at high strain rates were performed utilizing a split-Hopkinson pressure bar apparatus which resulted in strain rates in the order of 1000 s-1 and 3000 s-1. Compression tests at quasi-static strain rates were performed with an electro-mechanical loading machine and implementation of two-dimensional digital image correlation for strain measurements. With this method, strain rates in the order of 5 · 10-2 s-1 and 5 · 10-4 s-1 were achieved. The acquired results from the experimental tests included the response of the two materials at four different strain rates in the form of true stress-true strain curves. The results were indicative of small strain rate dependency for each of the two hardened steels with a slight increase in yield stress for increasing strain rates. Both materials exhibited closely similar characteristics. At quasi-static rates, the response of both materials exhibited work-hardening of closely similar characteristics. At high strain rates, the response of both materials exhibited a close to identical decrease in stress for values of strain exceeding 10 %. This behavior was suggested to be a consequence of adiabatic heating. At all four achieved strain rates, the results were indicative of a higher yield stress with higher subsequent stresses for one of the hardened steels in comparison to the other. The impact load case aimed to be simulated involved one swing of a brushcutter against a 25 mm diameter steel rod according to standard SS-EN ISO 11806-1:2011. The steel rod was specified to be impacted horizontally by the blade at an approaching translational velocity of 1 m/s and a blade rotational velocity of 8500 rpm. The multi-physics simulation software LS-DYNA was used to develop simulation models which consisted of two main parts, the blade and the rod and included two different blade geometries. As a result of a study regarding the suitability of different discretization techniques, the decision was made to implement the mesh-free particle method Smoothed Particle Galerkin (SPG) and to perform coupling with the finite element method (FEM). Two material models were developed based on the measured stress-strain response obtained through high strain rate compression testing. Several numerical models of the impact load case were produced, all of which entailed different sets of parameters. These included selection of blade material, failure strain, rod length and blade angle relative to the horizontal plane. Finally, two models were developed which were opposite in terms of assigned element formulation for the blade tip and the rod and otherwise identical. The results of the different models were then compared, namely in terms of resulting material failure of the blade after impact. It was concluded that SPG was the most suitable method of choice for the impact load case aimed to be simulated due to its ability to handle large deformation and the inclusion of the a bond-based failure mechanism. Furthermore, implementation of the SPG method resulted in deformation and failure considered to be of greater agreement to experimental test results compared to FEM.

Volvos trucks are used to carry boulders of varying sizes from different mining sites or construction sites. These boulders are loaded onto the dumper of the truck by a wheel-loader which drops the boulders from various heights causing an impulse like force which distributes throughout the frame and to the rest of the truck. Depending on the size and what height the boulders are being dropped from, the distributed forces can cause damage to important parts of the truck. An experiment done by Volvo has shown that a two-ton weight dropped from 3.5 meters caused some truck components to crack, such as flywheel housing. Since this is alerting and it is costly to do the experiment on all trucks that Volvo manufactures it is our objective to come up with a method based on Finite Element which would evaluate the rock loading case. By using ANSA as the pre-processor which helps set up the model before running a simulation, and Nastran and LS-DYNA as the FEM solvers, a result was obtained that is somewhat comparable with the measurements. In the Nastran model, no non-linearities such as contact were considered, while in LS-DYNA nonlinear contact between the weight and the dumper body was defined, which improved the results considerably. The key conclusion from the two results was that the contact definition used in LS-DYNA is necessary if accurate results are important. Since LS-DYNA uses an explicit numerical method the model can be made more complicated by including more nonlinearities in the model and it would not affect the computation to much or at all. Hence the method would be future proof.

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