Key Engineering Materials Vols. 592-593

Abstract: The addition of stiff aggregates into a relatively compliant matrix results, up to a certain limit, in an increase of the effective mortar stiffness. Conventional micromechanical models are not able to capture this limit and must be coupled with a fracture mechanics model predicting the formation of microcracks between aggregates due to shrinkage of matrix. The proposed model utilizes the Mori-Tanaka (MT) scheme together with an estimation of a crack density, based on requirements for the crack formation determined by a numerical analysis. As a result, the model involves a single phenomenological constant, and provides significant improvement over the basic MT scheme.

Abstract: Specific silicon nitride based materials are considered according to certain practical requirements of process, the influence of the grain size and orientation on the bridging mechanisms was found. Crack-bridging mechanisms can provide substantial increases in toughness coupled with the strength in ceramics. The prediction of the crack propagation through interface elements based on the fracture mechanics approach and cohesive zone model is investigated and from the amount of damage models the cohesive models seem to be especially attractive for the practical applications. Using cohesive models the behaviour of materials is realized by two types of elements. The former is the element for classical continuum and the latter is the connecting cohesive element. Within the standard finite element package Abaqus a new finite element has been developed; it is written via the UEL (users element) procedure. Its shape can be very easily modified according to the experimental data for the set of ceramics and composites. The new element seems to be very stable from the numerical point a view. The shape of the traction separation law for three experimental materials is estimated from the macroscopic tests, JR curve is predicted and stability of the bridging law is tested.

Abstract: The quality of the working rollers from ductile-cast-iron used for rolling rails is determined by the chemical and structural composition of the material of the rollers and the production technology. The requirements of the quality cannot be ensured without perfect knowledge of the course of solidification, cooling and heat treatment of the cast rollers as well as the kinetics of the temperature field of the casting and mould. An original application of ANSYS simulated the forming of the temperature field of the entire system comprising the casting, the mold and ambient. In the experimental investigation of temperature field, an original methodology for the measurement of the distribution of temperatures and heat flows in the roller-mould system had been developed and verified in the operation. The kinetics of the solidification has a measurable and non-negligible influence on the chemical and structural heterogeneity of the investigated type of ductile-cast-iron. Tying on to the results of the model of the temperature field of the cast rollers, an original methodology was developed for the measurement of chemical microheterogeneity. The chemical and structural heterogeneity of the cast roller is therefore a significant function of the method of melting, modification and inoculation and the successive procedures of risering, casting and crystallization after cooling.

Abstract: This paper deals with the use of the computer simulation for semiconductor chip attach investigation, where the wire bonding is the mostly used process. The main focus lays on the correct definition of the capillary trace, which is essential for creation of a good bond contact as for chip, as well for package or substrate pad. Several simulations for different shapes of loops were created and compared with real bonds, which were done based on the settings from the analysis.

Abstract: A comprehensive approach, including statistical physics and thermodynamics is required in the modelling of phenomena underlying the processes of deformation and fracture of solids. This work is devoted to the description of the damage to fracture transition, using statistically based thermodynamic model of mesocracks and mesoshifts evolution. Numerical simulation of quasistatic tensile experiment of vanadium plate specimen illustrated the influence of bulk and shear defects on stress-strain state.

Abstract: The multi-parameter fracture mechanics becomes more and more significant, because it is shown that it can help to describe fracture processes occurring in cracked specimens more precisely than conventional linear elastic fracture mechanics. In this paper, the concept based on the Williams expansion derived for approximation of stress/displacement crack-tip fields is presented and applied on a mixed-mode configuration. Two fracture criteria for estimation of the initial crack propagation angle are introduced. A parametric study is performed in order to investigate the dependence of the crack propagation angle on the stress intensity factors ratio. Influence and importance of taking into account the so-called higher-order terms of the Williams expansion are discussed and some recommendations are stated.

Abstract: The objective of this paper is the numerical modeling of elastically supported plate created from pre-stressed hollow core panels of Spiroll type by ANSYS program. Elasticity of supports is achieved by support beams, which are connected to plate by contact target pairs. Calculation is executed in time steps, which correspond to real loading steps. Evaluations of deformation in selected sections of the slab are presented, too.

Abstract: A 2D elastic-plastic FEM simulation of growing fatigue crack under combined mode I and II loading was performed. An inclined fatigue crack propagated in a sheet of an Al-alloy D16CT1. The effect of increasing mode-mixity on cyclic zone size, shape and the amount of dissipated energy was investigated.

Abstract: The complexity of calibration procedure for determination of Weibull distribution parameters as well as necessity to perform FEM calculations is one of the shortcomings of conventional versions of Local Approach (LA). This report presents an attempt to ascertain interrelation between local and global characteristics of fracture of pre-cracked and notched specimens of reactor pressure vessel steels, high-strength steels etc. Criterion of cleavage fracture initiation ahead of a crack (notch) is formulated. Dimensionless parameter characterizing the effect of embrittlement by the crack or notch is proposed on the basis of this criterion. Based on the findings of low-temperature tests of pre-cracked or notched specimens of structural steels, it is proved that this parameter may be determined by both local and global characteristics.

Abstract: Observations and analysis of samples from scanning electron microscopic (SEM) micrographs has been concerned in this work. The samples originate from fractured mechanical mode I tensile testing of a thin polymer film made of polypropylene used in the packaging industry. Three different shapes of the crack; elliptical, circular and flat, were used to investigate the decrease in load carrying capacity. The fracture surfaces looked similar in all studied cases. Brittle-like material fracture process was observed both by SEM micrographs and the experimental mechanical results. A finite element model was created in Abaqus as a complementary tool to increase the understanding of the mechanical behaviour of the material. The numerical material models were calibrated and the results from the simulations were comparable to the experimental results.