Papers by Keyword: Void Nucleation

Abstract: A mode I, centre crack, in ductile steel plate of finite dimensions is modeled in ANSYS software. Non-linear stress-strain data of steel are used. Plane strain case is adopted. A suitable value of far field tensile stress (pressure) is chosen such that EPFM condition prevails at the crack tip. Process and plastic zones are obtained at the crack tip. Desired values are noted. Areas of high stress and high strain are identified. Validation of void nucleation taking place ahead of crack tip and not exactly at the crack tip and coalescence of voids happening at the crack tip are confirmed from the results. Plots between the distance of desired location from the crack tip and load line stresses and strains are drawn. The plots are in accordance with the expectations.

Abstract: The study presents the numerical simulation of the void nucleation process due to decohesion of the interface between the matrix and inclusion of iron carbide Fe₃C, under high stress state triaxiality ratio, which is equal to 1.345. The analysis was conducted for S355J2G3 steel, commonly used in civil engineering structures. Special attention was paid to the determination of the value of void nucleation strain.

Abstract: The plastic behavior of the Ti-6Al-4V alloy includes several features as strength differential effect, anisotropy and yield strength sensitivity to temperature and strain rate. Monotonic tensions in the three orthogonal directions of the material are performed to identify the Hill '48 yield criterion. Monotonic compression and plane strain tensile tests are also included in the experimental campaign to identify the orthotropic yield criterion of CPB06. An assessment of the two models is done by comparing the yield loci and the experimental data points for different levels of plastic work. A first approach of the damage modelling of the Ti-6AL-4V alloy is investigated with an extended Gurson-Tvergaard-Needleman damage model based on Hill '48 yield criterion. Finite element simulations of the experiments are performed and numerical results allows checking force-displacement curves until rupture and local information like displacement and strain fields. The prediction ability of the Hill '48, CPB and extended Gurson models are assessed on simple shear and notched tensile tests until fracture.

Abstract: There have been many efforts to investigate and develop a mechanical plasticity, damage and failure models for metal alloys in the last couple of decades. These models (single and multi-damage parameters) are generally based on energy and constitutive equations to simulate the fracture and failure processes in metal alloys. The conventional fracture mechanics theory and its applications have been successfully employed to study fracture and failure processes. However, these methods have serious short comes in predicting the damage and failure in metal alloys where the fracture is dominated by the presence of defects like micro-voids (and their growth, nucleation and coalescence), oxides and inclusions. In the present study, following the in-depth study of damage initiation and progression in aluminium alloys, a frame work has been setup to develop a numerical model for damage accumulation. Based on the existing phenomenological damage theory, a mathematical basis for damage initiation and also damage accumulation under wide range of stress triaxiality (including near pure shear) has been developed. The damage model has been checked and verified using a result of experimental-simulation comparative study. The experiments have been carried out using samples made from squeezed and high pressure casting step plates. One of the main contributions of this paper is to show the advantages of using plasticity-based modified damage models to investigate the damage accumulation in cast aluminium alloys.

Abstract: In this paper a numerical investigation on the void nucleation behaviors under combined mechanical and thermal cycling conditions have been performed. A finite element unit cell model is conduct to calculate the local stress-strain field and describe the process of void nucleation from inclusion. Numerical results show that the thermal mismatch stress between the particles and matrix can assist the external load to cause interface debonding. Under certain mechanical and thermal cycling conditions, complicated stress and strain hystereses developed in the matrix. Both the plastic strain and plastic energy density of the interface will be accumulated during every thermal cycle. The plastic energy accumulation of the interface will first reach the debonding value and failure occurs. Based on the numerical calculation, a new energy based failure criteria is proposed to characterize the behaviors of void nucleation under combine mechanical and thermal cycling conditions.

Abstract: Effects of thermal cycling on the tensile strength of aluminum alloy welded joints are studied experimentally in this paper. The damage mechanisms are also analyzed based on the microstructure observations. Results reveal that certain thermal cycling can cause strength decrease especially at the heat affected zone of the aluminum alloy welded joint. The cyclic temperature and the external load are the key factors which influence the strength of the welded joint specimens, while the cyclic period has a minor effect in thermal cycling conditions. Microstructure analysis also shows that voids nucleation and evolution governs the damage process under thermal cycling condition.

Abstract: SiC particle reinforced aluminum metal matrix composites (SiCp/Al) were prepared by powder metallurgy method, and the volume fraction was 5% with size of 3.5 micron and 10 micron. Uniaxial tensile experiments were carried out and the fracture modes were observed. The results demonstrated that the SiC particles in matrix might improve the strength and elastic modulus of the material, but the plastic deformation ability of the material decreased obviously. Based on SEM observation on the microstructure, the boundary cell model (boundary cell finite element method, BCFEM) was established to consider the particle debonded from its surroungding matrix. The particle debonding described by nucleation and growth of voids in matrix，which was investigated using GTN(Gurson-Tvergaard-Needleman) model. The BCFEM model was valid to describe the damage behavior due to the accurate characterization for microstructure of the model.

Abstract: This paper shows the result of some metallographical examinations that have been carried out on low-alloyed Cr-Mo-V heat resistant steel. The aim of this research is to present and compare the advantages and disadvantages of the mainly applied metallographical methods. These techniques are optical microscopy, scanning electron microscopy, replica method and special applications of these methods. We have proved that using the investigated methods together gives much more information about the lifetime of the specimen than using these techniques particularly.