• Title/Summary/Keyword: brittle material

Search Result 477, Processing Time 0.031 seconds

On the tensile strength of brittle materials with a consideration of Poisson's ratios

  • Hu Guoming;Cho Heechan;Wan Hui;Ohtaki Hideyuki
    • 한국지구물리탐사학회:학술대회논문집
    • /
    • 2003.11a
    • /
    • pp.603-610
    • /
    • 2003
  • The influence of Poisson's ratio on the tensile strength of brittle materials is neglected in many studies. When brittle materials are loaded in compression or impact, substantial tensile stresses are induced within the materials. These tensile stresses are responsible for splitting failure of the materials. In this paper, the state of stress in a spherical particle due to two diametrically opposed forces is analyzed theoretically. A simple equation for the state of stress at the center of the particle is obtained. An analysis of the distribution of stresses along the z-axis due to distributed pressures and concentrated forces, and on diametrically horizontal plane due to concentrated forces, shows that it is reasonable to propose the tensile stress at the center of the particle at the point of failure as a tensile strength of the particle. Moreover, the tensile strength is a function of the Poisson's ratio of the material. As the state of stress along the z-axis in an irregular specimen tends to be similar to that in a spherical particle compressed diametrically with the same force, this tensile strength has some validity for irregular particles as well. Therefore, it can be proposed as the tensile strength for brittle materials generally. The effect of Poisson's ratio on the tensile strength is discussed.

  • PDF

Analysis of quasi-brittle materials at mesoscopic level using homogenization model

  • Borges, Dannilo C;Pituba, Jose J C
    • Advances in concrete construction
    • /
    • v.5 no.3
    • /
    • pp.221-240
    • /
    • 2017
  • The modeling of the mechanical behavior of quasi-brittle materials is still a challenge task, mainly in failure processes when fracture and plasticity phenomena become important actors in dissipative processes which occur in materials like concrete, as instance. Many homogenization-based approaches have been proposed to deal with heterogeneous materials in the last years. In this context, a computational homogenization modeling for concrete is presented in this work using the concept of Representative Volume Element (RVE). The material is considered as a three-phase material consisting of interface zone (ITZ), matrix and inclusions-each constituent modeled by an independent constitutive model. The Representative Volume Element (RVE) consists of inclusions idealized as circular shapes symmetrically and nonsymmetrically placed into the specimen. The interface zone is modeled by means of cohesive contact finite elements. The inclusion is modeled as linear elastic and matrix region is considered as elastoplastic material. A set of examples is presented in order to show the potentialities and limitations of the proposed modeling. The consideration of the fracture processes in the ITZ is fundamental to capture complex macroscopic characteristics of the material using simple constitutive models at mesoscopic level.

Effect on Material Property on the Frature Propagation Behavior (재료의 취성과 연성이 균열의 진전에 미치는 영향)

  • Jeong, Jaeyeon;Woo, Kyeongsik
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.42 no.11
    • /
    • pp.919-926
    • /
    • 2014
  • In this paper, the effect of material properties on fracture behavior was studied using cohesive zone model and extended finite element method. The rectangular tensile specimen with a central inclined initial crack was modeled by plane stress elements. In the CZM modeling, cohesive elements were inserted between every bulk elements in the predicted crack propagation region before analysis, while in the XFEM the enrichment to the elements was added as needed during analysis. The crack propagation behavior was examined for brittle and ductile materials. For thin specimen configuration, wrinkle deformation was accounted for by geometrically nonlinear post-buckling analysis and the effect of wrinkling on the crack propagation was investigated.

A Study on Micro Ultrasonic machining for Brittle Material Using Ultrasonic vibration (초음파 진동을 이용한 취성재료 가공기술에 관한 연구)

  • 이석우;최헌종;이봉구
    • Proceedings of the Korean Society of Precision Engineering Conference
    • /
    • 1997.10a
    • /
    • pp.969-972
    • /
    • 1997
  • Ultrasonic machining technology has been developed over recent years for he manufacture of cost-effective and quality-assured precision parts for several industrial application such as optics, semiconductors, aerospace, and automobile application. The past decade has seen a tremendous in the use of ceramic in structural application. The excellent thermal, chemical and wear resistance of these material can be realized because of recent improvement in the overall strength and uniformity of advanced ceramics. Ultrasonic machining, in which abrasive particles in slurry with water are presented to the work surface in the presence of an ultrasonic-vibrating tool, is process which should be of considerable interest, as its potential is not limited by he electrical or chemical characteristics of the work material, making it suitable for application to ceramics. In order to improve the currently used ultrasonic machining using ultrasonic energy, technical accumulation is needed steadily through development of exciting device of ultrasonic machine composed of piezoelectric vibrator and horn. This paper intends to further the understanding of the basic mechanism of ultrasonic machining for brittle material and ultrasonic machining of ceramics based in the fracture-mechanic concept has been analyzed.

  • PDF

A Study on the High Temperature Fatigue Behavior of Hot Forging Die STD61 Steel (STD61 열간 금형강의 고온피로거동에 관한 연구)

  • 여은구;이태문;이용신
    • Proceedings of the Korean Society of Precision Engineering Conference
    • /
    • 2002.05a
    • /
    • pp.711-714
    • /
    • 2002
  • Although recent research of metallic materials in high temperature fatigue have been much accomplished, many studies about brittle material as a die steel in high temperature fatigue does not have been reported. Especially, the study on the fatigue behavior over the transformation temperature is not studied sufficiently because of its difficult analysis and experiment. Therefore, reliable results of brittle material in high temperature fatigue behavior are needed. In this paper, stress-strain curves and stress-life curves in die STD61 steel at 700 and 900 are carefully examined, as the basic experimental data are used to predict from fatigue life over 700.

  • PDF

Evaluation of R-curve Behavior Analysis and Machinability of $Si_3N_4-hBN$ Machinable Ceramics ($Si_3N_4-hBN$ 머시너블 세라믹의 R-curve 거동분석과 가공성 평가)

  • 장성민;조명우;조원승;이재형
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.21 no.1
    • /
    • pp.61-70
    • /
    • 2004
  • Generally, ceramics are very difficult-to-cut materials because of its high strength and hardness. The machining process of ceramics can be characterized by cracking and brittle fracture. In the machining of ceramics, edge chipping and crack propagation are the principal reasons to cause surface integrity deterioration. Such phenomenon can cause not only poor dimensional and geometric accuracy, but also possible failure of the ceramic parts. Ceramics can be machined with traditional method such as grinding and polishing. However, such processes are generally cost-expensive and have low material removal rate. Thus, in this paper, to overcome these problems. BN powder, which gives good cutting property, is added for the fabrication of machinable ceramics by volume of 5,10,15,20,25 and 30%. And, mechanical properties, R-curve behavior and machining tests are carried out to evaluate the machining properties of the manufactured machinable ceramics.

Analysis of Cutting Parameters for $Si_3 N_4$-hBN Machinable Ceramics Using Tungsten Carbide Tool (초경공구를 사용한 $Si_3 N_4$-hBN 머시너블 세라믹 가공에서 절삭 파라미터 분석과 결정)

  • 장성민;조명우;조원승;박동삼
    • Transactions of the Korean Society of Machine Tool Engineers
    • /
    • v.12 no.6
    • /
    • pp.36-43
    • /
    • 2003
  • In machining of ceramic materials, they are very difficult-to cut materials because of there high strength and hardness. Machining of ceramics are characterized by cracking and brittle fracture. Generally, ceramics are machined using conventional method such as finding and polishing. However these processes are generally costly and have low MRR(material removal rate). This paper focuses on determining the optimal levels of process parameters for products with CNC machining center. For this purpose, the optimization of cutting parameters is performed based on experimental design method. A design and analysis of experiments is conducted to study the effects of these parameters on the surface roughness by using the S/N ratio, analysis of ANOVA and F-test. Cutting parameters, namely, cutting speed, feed and depth of cut are optimized with consideration of the surface roughness.

The Mechanics of Crack Formation Induced by Sliding on a Brittle Material (슬라이딩에 의해 취성재료에 발생하는 균열 성장에 관한 연구)

  • Kim, J.H.
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.12 no.11
    • /
    • pp.36-44
    • /
    • 1995
  • When sliding a hard cylinder along the surface of glass, periodic surface cracks appear on the flat surface due to tensile stresses induced by the slider. These cracks propagate into the substrate and will affect the fracture properties of a body. Crack spacings and the directions of crack propagation into glass were calculated numerically by applying the finite element method and linear elastic fracture mechanics. The calculated crack spacings were in the range of the experimental results. Stress intensity factors and crack extension angles depended on the radius of slider and the load, and from these two factors the possible directions of crack propagation were calculated. The calculated propagation directions were in good agreement with real crack propagation.

  • PDF

Mechanical Properties of Hot Working Die Steel and Fatigue Analysis Model of Casting Mold (열간 금형재의 기계적 성질과 주조금형 피로해석모델)

  • 여은구;황성식;이용신;곽시영;김정태
    • Proceedings of the Korean Society of Precision Engineering Conference
    • /
    • 2003.06a
    • /
    • pp.405-408
    • /
    • 2003
  • Generally, the life of casting mold is limited by fatigue fracture or dimensional inaccuracy originated from wear in high temperature. Although recent research of metallic materials in high temperature fatigue have been much accomplished, many studies on brittle material as a die steel in high temperature fatigue does not have been reported. Especially, the study on the fatigue behavior over the transformation temperature is not studied sufficiently because of its difficult analysis and experiment. Therefore, reliable results of brittle material in high temperature fatigue behavior are needed. In this paper, stress-strain curves and stress-life curves in die STD61 steel are carefully examined between room temperature and 90$0^{\circ}C$, as the basic experimental data are used to predict from fatigue life of casting mold.

  • PDF

Peridynamic simulation of brittle-ice crushed by a vertical structure

  • Liu, Minghao;Wang, Qing;Lu, Wei
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.9 no.2
    • /
    • pp.209-218
    • /
    • 2017
  • Sea ice is the main factor affecting the safety of the Arctic engineering. However, traditional numerical methods derived from classical continuum mechanics have difficulties in resolving discontinuous problems like ice damage. In this paper, a non-local, meshfree numerical method called "peridynamics", which is based on integral form, was applied to simulate the interaction between level ice and a cylindrical, vertical, rigid structure at different velocities. Ice in the simulation was freshwater ice and simplified as elastic-brittle material with a linear elastic constitutive model and critical equivalent strain criterion for material failure in state-based peridynamics. The ice forces obtained from peridynamic simulation are in the same order as experimental data. Numerical visualization shows advantages of applying peridynamics on ice damage. To study the repetitive nature of ice force, damage zone lengths of crushing failure were computed and conclude that damage zone lengths are 0.15-0.2 times as ice thickness.