Asymptotic stress field at the tip of an inclined crack terminating to an interface

This paper presents the numerical results for the asymptotic stress field and the fracture parameters at the tip of an inclined cracks terminating to a bi-material ceramic interface. The numerical analysis was carried out using FRANC2D/L fracture analysis code. A biaxial specimen was modeled for producing different mixed mode loads and two materials combinations of Al2O3 and ZrO2 were considered. The influence of the material combination and applied mixed mode load on the singularity orders, stress distributions and stress intensity factors is highlighted.This paper presents the numerical results for the asymptotic stress field and the fracture parameters at the tip of an inclined cracks terminating to a bi-material ceramic interface. The numerical analysis was carried out using FRANC2D/L fracture analysis code. A biaxial specimen was modeled for producing different mixed mode loads and two materials combinations of Al2O3 and ZrO2 were considered. The influence of the material combination and applied mixed mode load on the singularity orders, stress distributions and stress intensity factors is highlighted

Analysis of Printed Circuit Boards strains using finite element analysis and digital image correlation

This paper investigates the use of digital image correlation (DIC) and finite element analysis for strain measurement on Printed Board Circuits (PCBs). Circuit boards (PCBs) are designed to mechanically support and electrically connect an electronic component assembly. Due to screw assemblies, the surface level differences on which the PCB is placed, the process of assembling the electronic components induces a certain state of stress and deformation in the PCB. The main components affected are microprocessors due to the way they are glued to PCBs with BGA - Ball grid arrays (BGA). Digital Image Correlation (DIC) is a full-field contactless optical method for measuring displacements and strain in experimental testing, based on the correlation of images taken during test. The experimental setup is realized with Dantec Q-400 system used for image capture and Istra 4D software for image correlations and data analyses. The maximum level of the obtained strain is compared with the allowable limit. Finite element analysis (FEA) is a numerical method of analysis for stresses and strain in structures of any given geometry

Experimental and numerical investigations of the influence of real cracks on chloride ingress in concrete

oproti online verzi posunuté stránkováníExperimental and numerical results of a chloride ingress study conducted on samples drilled from different locations of a reinforced concrete slab, previously loaded until failure, are presented. The experimental part was carried on following the NT Build 492 standard for the non-steady state migration test, then a 3D model was developed using the Abaqus/Standard software based on the FEM in order to simulate chloride ingress in both uncracked and cracked concrete

Fracture parameters determination of polyurethane materials for application of SED criteria to notched components

AbstractLocal Strain Energy Density represents an engineering approach for assessing the brittle fracture of cracked and notched components. Experimental determination of fracture parameters (critical value of deformation energy Wc in a local finite volume around the notch tip and the radius of the control volume Rc) represents a key issue. The paper presents a methodology to determine these parameters using a notched tensile specimen. The obtained values will be used to predict the fracture for different types of notches and cracked specimens under mode I; for cracked specimens under mixed mode and mode II has proposed a new approach which confirms that PUR foams can be treated as brittle materials. The considered specimens are made of rigid polyurethane foams having different densities from 100 to 651 kg/m3

Finite Fracture Mechanics and Cohesive Crack Model: Size effects through a unified formulation

Finite Fracture Mechanics and Cohesive Crack Model can effectively predict the strength of plain, cracked or notched structural components, overcoming the classical drawbacks of Linear Elastic Fracture Mechanics. Aim of the present work is to investigate size effects by expressing each model as a unified system of two equations, describing a stress requirement and the energy balance, respectively. Brittle crack onset in two different structural configurations is considered: (i) a circular hole in a tensile slab; (ii) an un-notched beam under pure bending. The study is performed through a semi-analytical parametric approach. Finally, theoretical strength predictions are validated with experimental results available in the literature for both geometries, and with estimations by the point criterion in the framework of Theory of Critical Distances

LASER-BASED ADDITIVELY MANUFACTURED POLYMERS: A REVIEW ON PROCESSES AND MECHANICAL MODELS

Additive manufacturing (AM) is a broad definition of various techniques to produce layer-by-layer objects made of different materials. In this paper, a comprehensive review of laser-based technologies for polymers, including powder bed fusion processes (e.g. selective laser sintering, SLS) and vat photopolymerisation (e.g. stereolithography, SLA), is presented, where both the techniques employ a laser source either to melt or cure a raw polymeric material. The aim of the review is twofold: (i) to present the principal theoretical models adopted in the literature to simulate the complex physical phenomena involved in the transformation of the raw material into AM objects; (ii) to discuss the influence of process parameters on the physical final properties of the printed objects, and in turn on their mechanical performance. The models being presented simulate: the thermal problem along with the thermally activated bonding through sintering of the polymeric powder in SLS; the binding induced by the curing mechanisms of light-induced polymerisation of the liquid material in SLA. Key physical variables in AM objects, like porosity and degree of cure in SLS and SLA respectively, are discussed in relation to the manufacturing process parameters, as well as to the mechanical resistance and deformability of the objects themselves

Mechanical characterization of additively manufactured photopolymerized polymers

Photopolymerization, based on light-induced radical polymerization, is nowadays exploited in additive manufacturing (AM) technologies enabling to achieve high dimensional quality. The mechanical properties of the obtained material are heavily dependent on the chemistry of the photopolymer and on the way the AM process is performed. Here we study, through experiments and theoretical modeling, how the mechanical properties of liquid crystal shutter (LCD) printed photopolymers depend on the printing process setup, namely UV exposure time and layer thickness. To this end, a multi-physics simulation tool considering the light diffusion, chemical kinetics, and the micro-mechanics at the network level, has been developed

Brittle or Quasi-Brittle Fracture of Engineering Materials 2016

1Department of Engineering Design and Materials, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway 2Faculty of Mechanical Engineering, Politehnica University of Timisoara, Blvd. M. Viteazu, Nr. 1, 300222 Timisoara, Romania 3Fatigue and Fracture Research Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics, School of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran 4Institute of Strength Physics and Material Science, Department of Mechanical Engineering & Aeronautics, Russian Academy of Sciences, Siberian Branch, Tomsk 634021, Russia 5Laboratory of Technology & Strength of Materials (LTSM), Department of Mechanical Engineering & Aeronautics, University of Patras, 26500 Patras, Greec

Influence of printing parameters on the eligibility of plane-strain fracture toughness results for PLA polymer

The majority of manufacturers of polymer filaments for FDM technology rely their datasheets only on tensile tests, so their documentation usually lacks any data concerning fracture mechanics parameters. Having in mind the importance of fracture mechanics parameters in material design and application e.g., plane-strain fracture toughness, and the fact that it can be measured using only standard tensile grips, or three-point bending test fixture on a regular tensile testing machine, this practice offers vital information for AM components carrying the load. Anyhow, it is not always a simple task to satisfy all requirements of the standard for plane-strain fracture toughness assessment of plastic materials (ASTM D5045-14), as in the case of FDM technology due to many printing parameters that not only influence fracture toughness results, but also can question the eligibility of test results if crack propagation deviates from the expected path or if the specimens don't meet the size criterion necessary for achieving the plane-strain condition. These problems are tackled in this research on PLA polymer, a material widely used in FDM technology. For this research SENB specimens are prepared according to ASTM D5045-14 standard and tested on tensile testing machine using three-point bending test fixtur