• 자동차안전학회지
• /
• 제16권2호
• /
• pp.60-66
• /
• 2024

Computer simulation significantly reduces the high costs associated with actual crash tests and is expanding due to its ability to analyze various test results quantitatively that are difficult to measure in real tests. Research on evaluation technologies is limited according to the finite element analysis, which aims to replace structural verification testing. In this study, considerations for virtual crash tests were derived, and the validity of the zero-energy mode (hourglass mode) was analyzed as part of the considerations for validating the results of vehicle crash simulations. The study reflects on the considerations for virtual crash tests and the variation in hourglass coefficient values affects the occurrence of the hourglass mode. As the hourglass coefficient changes, the maximum hourglass energy reaches over 5% of the maximum internal energy, necessitating a conservative review. A comprehensive study of the maximum hourglass energy is required, considering additional analysis results for various models and collision conditions.

• Structural Engineering and Mechanics
• /
• 제37권2호
• /
• pp.253-256
• /
• 2011

• 한국정밀공학회지
• /
• 제12권3호
• /
• pp.32-41
• /
• 1995

In the analysis of metal forming processes by the finite element method, there are many numerical instabilities such as element locking, hourglass mode and shear locking. These instabilities may have a bad effect upon accuracy and convergence. The present work is concerned with improvement of stability and efficiency in two-dimensional rigid-plastic finite element method using various type of elemenmts and numerical intergration schemes. As metal forming examples, upsetting and backward extrusion are taken for comparison among the methods: various element types and numerical integration schemes. Comparison is made in terms of stability and efficiency in element behavior and computational efficiency and a new scheme of adaptive directional reduced integration is introduced. As a result, the finite element computation has been stabilized from the viewpoint of computational time, convergency, and numerical instability.

• Coupled systems mechanics
• /
• 제2권4호
• /
• pp.389-410
• /
• 2013

Three-dimensional Lagrangian fluid finite element is applied to seismic response analysis of an oil storage tank with a floating roof. The fluid element utilized in the present analysis is formulated based on the displacement finite element method considering only volumetric elasticity and its element stiffness matrix is derived by using one-point integration method in order to avoid volumetric locking. The method usually adds a rotational penalty stiffness to satisfy the irrotational condition for fluid motion and modifies element mass matrices through the projected mass method to suppress spurious hourglass-mode appeared in compensation for one-point integration. In the fluid element utilized in the present paper, a small hourglass stiffness is employed. The fluid and structure domains for the objective oil storage tank are modeled by eight-node solid elements and four-node shell elements, respectively, and the transient response of the floating roof structure or the free surface are evaluated by implicit direct time integration method. The results of seismic response analyses are compared with those by other method and the validation of the present analysis using three-dimensional Lagrangian fluid finite elements is shown.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1993년도 추계학술대회 논문집
• /
• pp.195-199
• /
• 1993

In the analysis of metal forming processes by the finite element method, there are many numerical instabilities such as element locking, hourglass mode, shear locking. These instabilities may have a bad effect upon accuracy and convergence. The present work is concerned with improvement of stability and efficiency in two dimensional rigid-plastic finite element method using various type of elements and numerical integration schemes. AS metal forming examples, upsetting and backward extrusion are taken for comparison among the methods : various element types and numerical integration schemes. comparison is made in terms of stability and efficiency. As a result, it has been shown that the finite element computation is stabilized from the viewpoint of computational time, convergency, and numerical instability.

• 대한기계학회논문집A
• /
• 제35권9호
• /
• pp.1119-1129
• /
• 2011

쇼트피닝(shot-peening) 처리를 한 베어링강의 고사이클 피로거동을 연구하였다. 열처리한 베어링강(JISSUJ2) 시험편과 열처리 후 쇼트피닝 표면가공을 추가한 시험편을 사용해 회전굽힘피로시험을 수행하고 파단 된 시험편의 파면을 분석하였다. 시험편의 피로파괴는 표면 결함에서 비롯된 표면 파괴와, 내부의 비금속개 재물에서 비롯된 내부형 파괴의 두 종류로 발생하였다. 내부 파괴의 경우 비금속 개재물 주변에 어안(fisheye) 모양의 파괴양식이 관찰되었다. 개재물은 표면으로부터의 깊이와 형상에 따라 피로 수명에 큰 영향을 주었다. 쇼트피닝 가공을 한 베어링강은 저사이클 하중영역 및 고사이클 하중영역에서 모두 피로수명이 향상되었으며, 하중이 작아질수록 피로수명의 개선은 더욱 커졌다. 또한 2 모수 와이블(Weibull) 분포를 이용하여 베어링강의 확률-응력-수명 (P-S-N) 곡선을 구하여 신뢰도 높은 피로수명 예측을 하였다.

• Structural Engineering and Mechanics
• /
• 제21권5호
• /
• pp.539-551
• /
• 2005

Finite elements based on isoparametric formulation are known to suffer spurious stiffness properties and corresponding stress oscillations, even when care is taken to ensure that completeness and continuity requirements are enforced. This occurs frequently when the physics of the problem requires multiple strain components to be defined. This kind of error, commonly known as locking, can be circumvented by using reduced integration techniques to evaluate the element stiffness matrices instead of the full integration that is mathematically prescribed. However, the reduced integration technique itself can have a further drawback - rank deficiency, which physically implies that spurious energy modes (e.g., hourglass modes) are introduced because of reduced integration. Such instability in an existing stiffness matrix is generally detected by means of an eigenvalue test. In this paper we show that a knowledge of the dimension of the solution space spanned by the column vectors of the strain-displacement matrix can be used to identify the instabilities arising in an element due to reduced/selective integration techniques a priori, without having to complete the element stiffness matrix formulation and then test for zero eigenvalues.

• Restorative Dentistry and Endodontics
• /
• 제31권2호
• /
• pp.103-112
• /
• 2006

본 실험에서는 자가부식형 접착제와 콤포짓트 레진 사이의 산도의 차이를 완화시킬 수 있는 접착레진을 자가부식형 접착제 위에 추가적으로 도포할 경우, 상아질에 대한 접착력을 개선할 수 있는지를 연구하였다. 자가부식형 접착제로는 실험실에서 직접 제작한 실험용 자가부식형 접착제 (pH: 1.96)와 Adper Prompt (3M ESPE, VSA, pH: 1.0)를 사용하였으며, 중성의 접착레진으로 All-Bond 2의 D/E bonding resin (Bisco Inc., USA, pH: 6.9)을 사용하였다. 두 대조군에서는 두 가지 자가부식형 접착제를 각각 두번씩 도포하였으며, 두 실험군에서는 각 자가부식형 접착제를 한번 도포한 후 그 위에 D/E bonding resin을 추가 도포하였다. Z-250 하이브리드 복합레진을 쌓아올려 모레시계 형태의 시편을 제작하여 미세인장강도를 측정하고 t-test를 이용하여 비교하였다. 파절 양상은 입체현미경과 주사전자현미경을 이용하여 관찰하였다. D/E bonding resin을 추가 도포한 미세 인장접착강도는 유의하게 증가되었고, 접착층과 복합레진 또는 접착층과 상아질 사이의 파절을 보인 시편의 수는 감소하고, 접착층 내의 파절을 보인 시편의 수는 증가되었다. 따라서 자가부식형 접착제와 복합레진의 산도의 차이를 완화할 수 있는 중성의 접착레진을 추가 도포할 경우 미세인장접착강도를 증가시킬 수 있음을 확인하였다.