• Title, Summary, Keyword: Mechanical fracture

Search Result 2,921, Processing Time 0.035 seconds

Mechanical Behavior and Numerical Estimation of Fracture Resistance of a SCS6 Fiber Reinforced Reaction Bonded Si$_3$N$_4$ Continuous Fiber Ceramic Composite

  • Kwon, Oh-Heon;Michael G. Jenkins
    • Journal of Mechanical Science and Technology
    • /
    • v.16 no.9
    • /
    • pp.1093-1101
    • /
    • 2002
  • Continuous fiber ceramic composites (CFCCs) have advantages over monolithic ceramics : Silicon Nitride composites are not well used for application because of their low fracture toughness and fracture strength, but CFCCs exhibit increased toughness for damage tolerance, and relatively high stiffness in spite of low specific weight. Thus it is important to characterize the fracture resistance and properties of new CFCCs materials. Tensile and flexural tests were carried out for mechanical properties and the fracture resistance behavior of a SCS6 fiber reinforced Si$_3$N$_4$ matrix CFCC was evaluated. The results indicated that CFCC composite exhibit a rising R curve behavior in flexural test. The fracture toughness was about 4.8 MPa$.$m$\^$1/2 , which resulted in a higher value of the fracture toughness because of fiber bridging. Mechanical properties as like the elastic modulus, proportional limit and the ultimate strength in a flexural test are greater than those in a tensile test. Also a numerical modeling of failure process was accomplished for a flexural test. This numerical results provided a good simulation of the cumulative fracture process of the fiber and matrix in CFCCs.

A Study on the Fracture Toughness Characteristics of Equivalent Stress Gradient Specimen (등가응력구배시편의 파괴특성에 관한 연구)

  • Park, Keon Tae;Shin, In Hwan;Kim, Ik Hyun;Kim, Yong Seok;Kwon, Hyuck Sam;Koo, Jea Mean;Seok, Chang Sung
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.31 no.6
    • /
    • pp.551-557
    • /
    • 2014
  • Ideally, it is preferable to obtain the fracture characteristics of a piping from the fracture toughness of real pipes. However, a fracture toughness test on real pipes not only incurs much expense, but is very difficult to perform. Therefore fracture toughness tests have been carried out with standard specimens instead of real pipes. But, the estimates of fracture toughness obtained from standard specimens are more conservative than those of real pipes owing to the difference in the constraint effect between real pipes and standard specimens. Therefore, we have been studied with equivalent stress gradient specimen (ESG) which is designed to behave equally compared to real pipe about stress gradient on crack tip. In this study, we will evaluate fracture characteristics of equivalent stress gradient specimen by using analytical methods and compare with those of real pipe. And finally investigate suitability of equivalent stress gradient specimen.

A study on the fracture toughness evaluating method for cryogenic structural material (극저온용 구조재료의 파괴인성평가법에 관한 연구)

  • Kwon, Il-Hyun;Chung, Se-Hi
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.22 no.1
    • /
    • pp.64-72
    • /
    • 1998
  • This paper was undertaken to develop the fracture toughness testing method using small and single specimen compared to the conventional method in evaluating elastic-plastic fracture toughness of the superconducting magnet structural material at cryogenic temperature. The elastic-plastic fracture toughness test was conducted by using the unloading compliance method recommended by ASTM E813-89 to accomplish the above purpose. And, the 20% side-grooved 0.5TCT and 1TCT specimens were used to evaluate the fracture toughness by using as possible as miniaturized CT specimen. The unloading compliance method was a very useful method in evaluating elastic-plastic fracture toughness at cryogenic temperature. It could be taken valid fracture toughness values by using 20% side-grooved 0.5TCT specimen recommended by ASTM E813-89.

A Study on the Evaluation Method of Mechanical Properties by Ball Indentation Method (압입법을 이용한 재료 물성치 평가 기법에 관한 연구)

  • Seok, Chang-Seong;Kim, Jeong-Pyo;Song, Seong-Jin;Kim, Hun-Mo;Kim, Jae-Won;Kim, Su-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.25 no.12
    • /
    • pp.1903-1910
    • /
    • 2001
  • The BI(Ball Indentation) method has a potential to assess the mechanical properties and to replace conventional fracture tests. In this study, the BI test system has been developed to evaluate material properties. Tensile tests, fracture toughness tests, hardness tests and BI tests were performed by the system using four classes of thermally aged specimens. The results of the BI tests were in good agreement with fracture characteristics from a standard fracture test method.

Evaluation of Fracture Toughness and AE Characteristics in Functionally Gradient Material by means of MSP Test (MSP 시험법에 의한 경사기능재료의 파괴인성 및 AE 특성 평가)

  • 송준희;임재규;정세희
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.19 no.3
    • /
    • pp.631-638
    • /
    • 1995
  • In this study, mechanical characteristics test of Functionally Gradient Materia (FGM) was performed by means of Modified Small Punch (MSP) Test with FGM; NiCrAlY-8YSZ and PSZ-Ni. To determine fracture mechanic factor, it was carried out MSP test that has possibility with small specimen (10*10*0.5 mm$^{t}$ ) and AE test to analyze micro fracture mechanism. As a result, fracture behavior became varied from brittle fracture to ductile as the content of Ni(or NiCrAlY) composition was increased and fracture energy was increased too. AE characteristics demonstrated that AE technique can detect the onset of fracture processes and AE energy was suddenly increased in the vicinity of maximum load. Since Young's modulus, fracture stress and fracture toughness was determined by MSP test, it can be known that the composition of NiCrAly 75%/8YSZ25% has the best mechanical property and furthermore this result is supported with fracture surface observation.

Mechanical Behavior and Fracture Resistance of $SCS6/Si_3N_4$ CFCCs ($SCS6/Si_3N_4$ 연속섬유강화 세라믹 복합재료의 기계적 거동 및 파괴저항평가)

  • Yoon, Yu-Sung;Kwon, Oh-Heon;Jenkins, Michael G.
    • Proceedings of the KSME Conference
    • /
    • /
    • pp.658-662
    • /
    • 2001
  • Continuous fiber ceramic composites(CPCCs) having the advantages of ceramics resistance to heat, eroson can be applied in chemical reactors and engine. CFCCs has relatively high stiffness in spite of low weight. In particular, it exhibits greatly increased toughness, which serves to decrease its inherent damage characteristics of the brittle nature of monolithic ceramics. In this wort, tensile and flexural test for SCS6 fiber/ $Si_3N_4$ matrix composites were studied. An objective of this study is to obtain the basic quantities of mechanical properties for tension and flexural test and link these to the fracture resistance behavior. Then, we showed that wok of fracture concept was useful as a method for describing fracture restance behavior of CFCCs.

  • PDF

An Evaluation Method of Probability of Elastic-Plastic Fracture by 2-Parameter Criterion

  • Kim, Tae-Sik;Yoon, Han-Yong;Lim, Myung-Hwan;Jung, Ui-Jung
    • Journal of Mechanical Science and Technology
    • /
    • v.18 no.1
    • /
    • pp.55-64
    • /
    • 2004
  • Many researchers have made a lot of progress in studying the evaluation of fracture probability of brittle materials. However, studies of fracture probability for elastic-plasticity have not been made yet. An evaluation method for fracture probability which is grafted onto a 2-parameter criterion and statistical probability analysis is not only introduced in this study, but also applied to the simple 2-dimensional model and carbon steel piping to vealuate the effect of statistical variables.

A Study on the Fracture Mode Characteristics of Automotive Application Component Lead-free Solder Joints (자동차 전장부품 무연솔더 접합부의 파괴모드 특성에 관한 연구)

  • Jeon, Yu-Jae;Kim, Do-Seok;Shin, Young-Eui
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.19 no.6
    • /
    • pp.90-96
    • /
    • 2011
  • In this study, the characteristic of fractured portion and shape on solder joints were investigated according to the thermal shock test for Automotive Application Component using Sn-3.0Ag-0.5Cu solder, which has a outstanding property as Lead-free solder. The value of pull and shear strength was decreased in principle after 432 cycles thermal shock test. In addition, fracture mode was verified by using EDS and SEM to observe fractured shape on the solder joints before and after thermal shock. In before thermal shock test, the fracture mode revealed typically solder layer's fracture mode. In after thermal shock test, we identified multiple fracture mode of the ductile and brittle fracture. Even though same composition of solder was used to experimental for estimating. the fracture mode varied on the fracture portion's height and the directional angles of shear strength. In conclusion, we identified that mechanical strength was affected on the solder layer's fracture mode.

Study on the Effects of Surface Treatment and Stitching on the Fracture Behavior of Composite Laminates (계면처리와 스타칭이 복합적층판의 파괴거동에 미치는 영향 연구)

  • Hong, S.Y;Hwang, W;Park, H.C;Han, K.S
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.20 no.3
    • /
    • pp.806-815
    • /
    • 1996
  • The interlaminar fracture behavior of woven laminates under static and cyclic loadings has been studied using DCB(double cantilever beam) specimens. The effects of surface treatment and stiching on the fracture behavior of composite laminates are investigated experimentally. Fracture toughness has been improved by surface treatment because the surface treatment can change the fracture mechanism of laminates. SCB(stitched cantilever beam) model has been proposed to quantify the effect of through-thickness resinforcement(stiching) in improving the delamination crack growth resistance. Distributed loads which are transfered to through-thickness fibers can be calculated by the SCB model. And fracture energy increase due to the distributed load can be predicted by a power function of the distributed load. A new parameter agreed well proposed predict fatigue crack growth rate. The predictions using this parameter agreed well with the experimental data.

The Effect of residual stress on fracture behavior in the laser weldment (레이저용접부의 파괴에 미치는 잔류응력의 영향)

  • Cho, Sung-Kyu;Yang, Young-Soo;Noh, Young-Jin
    • Laser Solutions
    • /
    • v.11 no.2
    • /
    • pp.1-7
    • /
    • 2008
  • The integrity of laser welded structures is decided in fracture strength and fatigue strength. This study made an effort to understand the fracture behavior considering residual stress. Experiments are conducted and analyses are performed to explore the influence of residual stress on fracture behavior of bead-on laser welded compact specimen. Fracture experiments are performed using ASTM 1820. The performed analyses included thermo-elasto-plastic analyses for residual stress and subsequent J-integral calculation. A modified J integral is calculated in the presence of residual stresses. The J-integral is path-independent for combination of residual stress field and stress due to mechanical loading. The results indicates that the tensile residual stress near crack front bring the low fracture load while the compressive residual stress bring the high fracture load compared to no residual stress specimen. These results quantitatively understand the influence of residual stress on fracture behavior.

  • PDF