• 제목/요약/키워드: Crack evolution

검색결과 126건 처리시간 0.021초

내부크랙을 가지며 비틀림모멘트를 받는 중공축의 응력해석 (Stress Analysis of Hollow Cylinder with Inner Cracks Subjected to Torsion Moment)

  • 이종선;하영민
    • 한국생산제조학회지
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    • 제7권5호
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    • pp.46-52
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    • 1998
  • In fracture problems, stress intensity factors obtained theoretically and experimentally have been effectively utilized in the analytical evolution of the cracks effect. The effect of surface crack of a cylindrical and a hollow cylindrical bar is investigated, as well as the effect of the thickness of a hollow cylindrical bar and inclined crack of a hollow cylinder subjected to torsion moment. In this study, stress intensity factor Km of mode III which expresses the stress state in the neighborhood of a crack tip is used. stress analysis was conducted on the inside of hollow cylinder inthe axial direction of three dimensional crack tip subjected to torsion moment by combining the caustics method and the stress freezing method.

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치아 응용을 위한 /유리침윤 알루미나 이중 층상구조의 접촉손상 및 파괴 (Contact Damage and Fracture of Poreclain/Glass-Infiltrated Alumina Layer Structure for Dental Application)

  • 정연길;여정구;최성설
    • 한국세라믹학회지
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    • 제35권12호
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    • pp.1257-1265
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    • 1998
  • Hertzian contact tests were used to investigate the evolution of fracturedamage in the coating layer as functions of contact load and coating thickness by studying crack patterns in porcelain on glass-infiltrated alumina bilayer system conceived to simulate the crown structure of a tooth. Cone cracks initiated at the coating top surface without delamination at interface and crack propagation to substrate. Preferentially the cracks made multi-cracks at the coating top surface rather than proceeding to interface. The cracks were highly stabilized with wide ranges between the loads to initiate first cracking and to cause final failure im-plying damage-tolerant capability. Finite element modelling was used to evaluate the stress distribution. Maximum tensile stress were responsible for the cracking at the coating layer and had a profound influence on the crack pattern and fracture damage in the layered structure materials.

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Plastic energy approach prediction of fatigue crack growth

  • Maachou, Sofiane;Boulenouar, Abdelkader;Benguediab, Mohamed;Mazari, Mohamed;Ranganathan, Narayanaswami
    • Structural Engineering and Mechanics
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    • 제59권5호
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    • pp.885-899
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    • 2016
  • The energy-based approach to predict the fatigue crack growth behavior under constant and variable amplitude loading (VAL) of the aluminum alloy 2024 T351 has been investigated and detailed analyses discussed. Firstly, the plastic strain energy was determined per cycle for different block load tests. The relationship between the crack advance and hysteretic energy dissipated per block can be represented by a power law. Then, an analytical model to estimate the lifetime for each spectrum is proposed. The results obtained are compared with the experimentally measured results and the models proposed by Klingbeil's model and Tracey's model. The evolution of the hysteretic energy dissipated per block is shown similar with that observed under constant amplitude loading.

미세역학이론에 의한 콘크리트의 응력-변형도 관계와 연성도의 예측에 관한 연구 (Prediction of Stress-Strain Relation and Evolution of Compliance of Concrete by a Micromechanical Model)

  • 김진구
    • 콘크리트학회지
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    • 제8권3호
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    • pp.147-155
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    • 1996
  • 본 연구에서는 미세역학모델을 이용하여 무근 콘크리트의 응력-변형도관계를 예측할 수 있는 모델을 제시하였다. 모델에서는 하중이 가해지기 전에 골재와 모르터의 경계면에 초기 균열이 존재한다고 가정하고 하중에 의한 부착균열과 모르터균열의 형성여부를판별하기 위하여 선형탄성파괴역학(LEFM) 이론을 사용하였다. 또한 계산의 편의를 위하여 이러한 부착균열-몰타균열의 결합된 형상을 등가 직선균열로 치환하여 해석하였다. 발생된 균열의 크기와 그 밀도로부터 손상된 콘크리트의 연성도와 변형의 증가량을 계산하고 발표된 실험결과와 비교하여 보았다. 그 결과 본 모델에 의한 응력-변형도 관계의 예측은 압축보다는 인장에, 보통 콘크리트보다 고강도 콘크리트에 더 잘 적용됨을 발견하였다.

Characteristics of AE Signals from Fatigue Crack Propagation and Penetration of a Surface Crack in 6061 Aluminum Plate

  • Ahn, Seok-Hwan;Nam, Ki-Woo
    • International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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    • 제4권1호
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    • pp.44-50
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    • 2001
  • Existing surface defects in structural members often act as sites of fatigue crack initiation, and if undetected, these cracks may grow through the thickness of the member, leading to catastrophic failure of the structure. Thus, in-service monitoring of fatigue cracks through reliable and effective nondestructive techniques is an important ingredient in the leak-before-break (LBB) design and safe operation of defects critical structures. An advanced, waveform-based, acoustic emission (AE) technique has been used in this paper to study the characteristics of the signals emanating from the initiation, growth and through-the -thickness penetration of surface fatigue crack in a 6061 aluminum plate. The goal of this experimental study is to determine whether the evolution of the fatigue crocks could be identified from the properties of the waveforms produced during the tests. The AE waveform signals detected at different stages of crack growth was found to have different temporal and spectral characteristics. The data analysis technique presented here can be applied to real-time monitoring of the initiation and propagation of fatigue cracks in structural components.

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압입축에 발생하는 프레팅 마모가 피로수명에 미치는 영향 (The Effect of Fretting Wear on Fatigue Life of Press-fitted Shaft)

  • 이동형;권석진;최재붕;김영진
    • 대한기계학회논문집A
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    • 제31권11호
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    • pp.1083-1092
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    • 2007
  • The objective of the present paper is to evaluate the effect of the evolution of contact surface profile caused by fretting wear on fatigue life of press-fitted shaft by means of an analytical method based on experimental data. A finite element analysis was performed to analyze the stress states of press-fitted shaft, considering the worn contact profiles of shaft. The fatigue lives of the press-fitted shaft reflecting the evolution of contact stress induced by fretting wear were evaluated by stress-life approach using fatigue notch factor. It is found that the stress concentration of contact edge in press-fitted shaft decreases rapidly at the initial stage of total fatigue life, and its location shifts from the contact edge to the inside with increasing number of fatigue cycles. Thus the change of crack nucleation position in press-fitted shaft is mainly caused by the stress change of contact edge due to the evolution of contact surface profile by fretting wear. Furthermore, the estimated fatigue lives by stress-life approach at the end of running-in period of the fretting wear process corresponded well to the experimental results. It is thus suggested that the effect of fretting wear on fatigue life in press fits is strongly related to the evolution of surface profile at the initial stage of total fatigue life.

압입축에 발생하는 프레팅 피로균열 발생 및 진전 특성 실험 (Experimental Study on Fatigue Crack Initiation and Propagation due to Fretting Damage in Press-fitted Shaft)

  • 이동형;권석진;최재붕;김영진
    • 대한기계학회논문집A
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    • 제31권6호
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    • pp.701-709
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    • 2007
  • To clarify the characteristics of surface damage due to fretting in press-fitted shaft, experimental methods were applied to small scale specimen with different bending load condition. Fatigue tests and interrupted fatigue tests of press-fitted specimen were carried out by rotate bending fatigue test. Macroscopic and microscopic characteristics were examined using scanning electron microscope (SEM), optical microscope or profilometer. It is found that small fatigue cracks are nucleated early in life regardless of bending stress, and thus the most portion of fatigue life on press fits can be considered to be crack propagation process. Most of surface cracks are initiated near the contact edge, and multiple cracks are nucleated and interconnected. Furthermore, the fretting wear rates at the contact edge are increased rapidly at the initial stage of total fatigue life. It is thus suggested that the fatigue crack nucleation and propagation process is strongly related to the evolution of surface profile by fretting wear in press fits.

Dynamic prediction fatigue life of composite wind turbine blade

  • Lecheb, Samir;Nour, Abdelkader;Chellil, Ahmed;Mechakra, Hamza;Ghanem, Hicham;Kebir, Hocine
    • Steel and Composite Structures
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    • 제18권3호
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    • pp.673-691
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    • 2015
  • In this paper we are particularly focusing on the dynamic crack fatigue life of a 25 m length wind turbine blade. The blade consists of composite materiel (glass/epoxy). This work consisted initially to make a theoretical study, the turbine blade is modeled as a Timoshenko rotating beam and the analytical formulation is obtained. After applying boundary condition and loads, we have studied the stress, strain and displacement in order to determine the critical zone, also show the six first modes shapes to the wind turbine blade. Secondly was addressed to study the crack initiation in critical zone which based to finite element to give the results, then follow the evolution of the displacement, strain, stress and first six naturals frequencies a function as crack growth. In the experimental part the laminate plate specimen with two layers is tested under cyclic load in fully reversible tensile at ratio test (R = 0), the fast fracture occur phenomenon and the fatigue life are presented, the fatigue testing exerted in INSTRON 8801 machine. Finally which allows the knowledge their effect on the fatigue life, this residual change of dynamic behavior parameters can be used to predicted a crack size and diagnostic of blade.

매스콘크리트 수화발열 특성의 정량화를 위한 실험적 연구 (An Experimental Study on the Quantification of Hydration Heat Evolution in Mass Concrete)

  • 이장화;변근주
    • 한국콘크리트학회:학술대회논문집
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    • 한국콘크리트학회 1994년도 봄 학술발표회 논문집
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    • pp.238-242
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    • 1994
  • Recently, construction of mass concrete structures except Dam are increased very often. Generation heat due to the hydrating reaction of mass concrete is generally larger than the heat released to the air, foundations and the exist structures. Therefore, internal temperature of mass concrete is remarkably risen and temperature gap between center and surface is extended by various effect. It this gap get large, the crack may be occurred. This crack must be controlled as little as possible to ensure the soundness and durability of structure. Firstly, Temperature rising history of Mass concrete is expected correctly to constrain the crack of mass concrete. So, objectives of this research is to quantify the effects of hydration temperature for the purpose of evaluating accurately the temperature history of mass concrete.

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Study on fracture mechanics of granite specimens with different precast notch depths based on DIC method

  • Shuwen Cao;Hao Shu
    • Geomechanics and Engineering
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    • 제33권4호
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    • pp.393-400
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    • 2023
  • Displacements near crack and stress intensity factor (SIF) are key parameters to solve rock failure issue when using fracture mechanics. In order to study the horizontal displacement and stress intensity factor of the mode I fracture, a series of three-point bending tests of granite specimens with central notch were carried out. The evolution of horizontal displacements of precast notch and crack tip opening displacements (CTOD) were analyzed based on the digital image correlation (DIC) method. Stress intensity factors for three-point bending beams with arbitrary span-to-width ratios(S/W) were calculated by using the WU-Carlsson analytical weight function for edge-crack finite width plate and the analytical solution of un-cracked stress by Filon. The present study provides a high efficient and accurate method for fracture mechanics analysis of the three-point bending granite beams.