Key Engineering Materials Vols. 577-578

Abstract: In this paper the development of a computational model for the thermal conductivity design for locally orthotropic materials is presented. The material orientation of a two-dimensional locally orthotropic solid subjected to thermal loads is designed for minimization of the local temperature. Two optimization problems are considered: the minimization of the highest (hot-spot) temperature and the minimization of the temperature according to the weights distribution. For both problems rules for calculation of the optimal material orientation are derived analytically. The analysis is based on the idea of the principal stresses method for optimization of material orientation in linear elasticity problems. The results of the analysis are implemented and the developed computational model is tested on an example of the lamella orientation optimization in a metal-ceramic composite.

Abstract: The optimization of the patch shape of bonded composite repair in aircraft structures is an efficient way to improve the repair performance. In this study the three-dimensional nonlinear finite element method is used to determine the J integral variation along the front of repaired crack with bonded composite patch in aircraft structures. The experimental design method was applied to optimize the patch shape and size in order to determine the most influencing dimension on the repair efficiency.

Abstract: This letter describes the work conducted at our laboratory for the implementation of an automated vision system for fatigue crack growth measurement. The system relies on a dedicated illumination system with grazing incidence and optimized feature extraction by morphological image processing and continuous calculation of the crack growth, for adjustment of the optimal time interval for image registration.

Abstract: In this Paper, Time-Harmonic Dynamic Crack Analysis in Two-Dimensional (2D), Layered and Linear Piezoelectric Composites is Presented. A Frequency-Domain Symmetric Galerkin Boundary Element Method (SGBEM) is Developed for this Purpose. the Piecewise Homogeneous Sub-Layers of the Piezoelectric Composites are Modeled by the Multi-Domain BEM Formulation. the Frequency-Domain Dynamic Fundamental Solutions for Linear Piezoelectric Materials are Applied in the Present BEM. the Boundary Integral Equations are Solved Numerically by a Galerkin-Method Using Quadratic Elements. an Iterative Solution Algorithm is Implemented to Consider the Non-Linear Semi-Permeable Electrical Crack-Face Boundary Conditions. Numerical Examples will be Presented and Discussed to Show the Influences of the Location and Size of the Crack, the Material Combination of the Sub-Layers, the Piezoelectric Effect and the Time-Harmonic Dynamic Loading on the Dynamic Intensity Factors.

Abstract: In previous papers, the energy dissipated to the surroundings as heat in a unit volume of material per cycle, Q, has been successfully applied to correlate experimental data generated from push-pull, stress- or strain-controlled fatigue tests on AISI 304 L stainless steel plain and notched specimens. In this paper the fatigue behaviour of AISI 304 L un-notched bars under fully-reversed axial or torsional loading was investigated. By using the Q parameter it was found that the experimental data collapse into the same energy-based scatter band previously determined with the push-pull tests. The results found in the present contribution are meant to be specific for the material investigated.

Abstract: The damage tolerance methodology is used here to compare impact damage from experimental testing and virtual (numerical) testing. The first part of the study aims to identify links between experimental internal (delaminated area) and external measurable damage (dent depth) for a typical aeronautical T800S/M21e laminate. Effects of the mass/velocity ratios at some level of impact energy are evaluated. It is shown that a big mass generates denser and larger delamination with about the same dent than a small mass, which is a critical case for damage tolerance analysis. A relation between the external dent depth and internal delaminated area is proposed.

Abstract: The Low through-the-Thickness Strengths of Composites make them Prone to Delamination and Brutal Rupture. for Primary Aircraft Structural Components, it is Necessary to Predict Failure with Adequate Criteria for any Structure of Various Thicknesses and in Zones of Material or Geometric Discontinuities. the Purpose of the Present Work is to Evaluate the Ability of our Continuous Damage Model to Predict at which Interface Delamination will Occur in any Geometrical or Material Configuration. Numerical Predictions of Delamination Onset Computed by our CDM Model Show a Good Agreement with Theoretical Estimations and Experimental Results of an L-Shape Structure Reference Case. Comparisons between 2D and 3D Models Show no Effect of Free Boundaries on Delamination Onset and Growth.

Abstract: The particles distinct element model has the consistency to model the mechanical behavior of the microscopic structures inside an asphalt mixture. The model assumes that the schematized granular constituents are in a contact point, considering the thin asphalt films as the binding elements. In this paper, we will model (at micro-scale) the damage to a surface in asphalt concrete under an impulsive load, considering binding, interface, viscosity and friction. Our aim is to reproduce the micro-damage due to detachment among the elementary components of the concrete in airports pavements.The proposed approach is mainly from a mechanical point of view, and a general model describing adhesive contact between rigid bodies is proposed. The intensity of adhesion is supposed to decrease under prescribed shear and normal displacement fields and comes by energy reduction, where the viscosity and friction contributes are taken in account.A numerical implementation by finite element procedures has been performed, and the outcome is presented.

Abstract: Recent development in mechanical technologies and processes have shown that by performing traditional mechanical treatments with unusual and severe parameters it is possible to obtain metal surfaces characterized by grain size with dimension in the order of 50-100 nm. This confers peculiar and superior properties to the surface layer of material. Since the surface is the usual point of fatigue crack initiation it is expected that the parts treated this way show a better fatigue behavior with respect to the coarse grain materials, even if treated with conventional mechanical treatments. This work explores any opportunities to obtain nano-structured surface layers by means of two popular mechanical treatments, shot peening and deep rolling. To this end particularly severe processing parameters are applied on a low alloy steel fatigue test specimens. The treated surface is characterized by means of optical Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) analysis of residual stress and roughness measurements. In the end a series of fatigue tests on smooth specimens severely treated, conventionally treated and not treated were executed. The results show the potential benefits of severe mechanical treatments and were interpreted in the light of peculiar effects of these novel treatments on the characteristics of the treated surfaces.

Abstract: Study presented in this paper is concerned with fatigue crack initiation detection, crack propagation observation and measurement as well as with numerical simulation of damage accumulation and propagation in the nodular cast iron grade EN-GJS-400-18-LT. Material properties of nodular cast iron are well elaborated in previous authors' papers. Crack initiation and its propagation observation as well as crack length measurement is performed on standardized specimens using ARAMIS 4M optical system. Based on the experimental results, a new three-dimensional constitutive model is proposed to simulate the low-cycle fatigue behaviour of considered material. An efficient algorithm for modelling cyclic plasticity is used for performing numerical simulation of crack initiation and growth on standardized specimens made from nodular cast iron. The computational procedure accuracy is verified by comparing the computed results with the real experimental data.