• International Journal of Automotive Technology
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• v.2 no.1
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• pp.9-16
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• 2001

The lifetime of power train components can be improved dramatically by finding crack initiation points with suitable software tools and optimization of the critical areas. With increasing capacities of computers the prediction of the lifetime for components by numerical methods gets more and more important. This paper discusses some applications of the outstanding fatigue simulation program FEMFAT supporting the assessment of uniaxially and multiaxially loaded components (as well as welding seams and spot joints). The theory applied in FEMFAT differs in some aspects from classical approaches like the nominal stress concept or the local one and can be characterized by the term "influence parameter method". The specimen S/N-curve is locally modified by different influence parameters as stress-gradient to take into account notch effects, mean-stress influence which is quantified by means of a Haigh-diagram, surface roughness and treatments, temperature, technological size, etc. It is possible to consider plastic deformations resulting in mean-stress rearrangements. The dynamic loading of power train components is very often multiaxial, e.g. the stress state at each time is not proportional to one single stress state. Hence, the directions of the principal axes vary with time. We will present the way how such complex load situations can be handled with FEMFAT by the examples of a crank case and a gear box.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.1
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• pp.71-79
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• 2010

One of methods that accomplish fuel-efficient vehicle is to reduce the overall vehicle weight by using aluminum structure typically for cross members, rails and panels in body and chassis. For aluminum structures, the use of Self Piercing Rivet(SPR) is a relatively new joining technique in automotive manufacture. To predict SPR fatigue life, fatigue behavior of SPR connections needs to be investigated experimentally and numerically. Tests and simulations on lap-shear specimen with various material combinations are performed to obtain the joining strength and the fatigue life of SPR connections. A Finite element model of the SPR specimen is developed by using a FEMFAT SPR pre-processor. The fatigue lives of SPR specimens with the curvature are predicted using a FEMFAT 4.4e based on the liner finite element analysis.

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.310-312
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• 2006

Self-piercing riveting(SPR) is becoming an important joining technique for automotive application of various material sheets and shapes. Fatigue behavior of SPR conections needs to be investigated experimentally and numerically to predict SPR fatigue lives. The simulations of various SPR specimens (Coach-Peel specimen, Cross-Tension specimen, Tensile-Shear specimen, Pure-Shear specimen) are performed to predict the fatigue life of SPR connections under different material combinations. Finite element models of various SPR specimens are developed using a FEMFAT SPOT SPR pre-processor. The fatigue lives of SPR specimens are predicted using a FEMFAT 4.4e based on the liner finite element analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.8 s.227
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• pp.1174-1182
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• 2004

Recently, Self Piercing Rivet(SPR) has been spotlighted in the automotive industry as a substitutive resort of spot welding and has also been watched by the designer as lightening a car body due to their superior assembly processes. Fatigue behavior of SPR joint needs to be investigated experimentally and numerically to predict its structural stiffness and fatigue life. Testing of lap-shear specimens with various material combinations is performed to obtain the joining strength and the fatigue life of SPR connections. The simulation of SPR lap-shear specimens is also conducted to obtain the structural stiffness of SPR connections under different material combinations. A Finite element model of the SPR lap-shear specimen is developed using a FEMFAT SPR pre-processor. The fatigue lift of SPR specimen is predicted using a FEMFAT 4.4e based on the liner finite element analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.2
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• pp.81-93
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• 2020

The fatigue characteristics of glass fiber reinforced plastic (GFRP) composites were studied under repeated loads using the finite element method (FEM). To realize the material characteristics of GFRP composites, Digimat, a mean-field homogenization tool, was employed. Additionally, the micro-structures and material models of GFRP composites were defined with it to predict the fatigue behavior of composites more realistically. Specifically, the fatigue characteristics of polybutylene terephthalate with short fiber fractions of 30wt% were investigated with respect to fiber orientation, stress ratio, and thickness. The injection analysis was conducted using Moldflow software to obtain the information on fiber orientations. It was mapped over FEM concerned with fatigue specimens. LS-DYNA, a typical finite element commercial software, was used in the coupled analysis of Digimat to calculate the stress amplitude of composites. FEMFAT software consisting of various numerical material models was used to predict the fatigue life. The results of coupled analysis of linear and nonlinear material models of Digimat were analyzed to identify the fatigue characteristics of GFRP composites using FEMFAT. Neuber's rule was applied to the linear material model to analyze the fatigue behavior in LCF regimen. Additionally, to evaluate the morphological and mechanical structure of GFRP composites, the coupled and fatigue analysis were conducted in terms of thickness.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.3
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• pp.91-97
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• 2004

The door closer is a typical system which consists of spring and damper. The door closer is a device to close the door more slowly. The virtual prototypes of cylinder-type door closer are developed. The simulations of virtual prototype are performed to obtain the load history of the guide pin. The structural strength assessment of the guide pin is performed to verify a design safety. The fatigue life and damage of the guide pin are predicted using a FEMFAT 4.3h based on the finite element analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.1
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• pp.63-69
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• 2008

A fatigue test on the steel welded L-shaped frame was conducted. The frame was consisted with carbon steel tube and reinforced bracket. The four type reinforced brackets were fabricated. They were two rectangular plate reinforced bracket, two sided pentagon plate reinforced bracket, triangular plate reinforced bracket and fully reinforced bracket. The fatigue test of frame was conducted with axial tension loading. The fatigue simulation of the steel welded L-shaped frame was also performed by the finite element method with code FEMFAT. The frame of fully reinforced bracket had the highest fatigue life and reinforced quality factor.

• Korean Journal of Computational Design and Engineering
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• v.12 no.6
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• pp.466-471
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• 2007

Brackets for an automatic transmission are usually used to connect the transmission with adjacent components in a vehicle. Fillet areas of brackets are one of the most important areas to design the brackets because the areas are easily fractured when the brackets are subjected to external loads. In this study, a new design around the fillet area of the bracket is suggested and improved effects of the proposed design are proved through the comparison of safety factors with the current design. The safety factors are calculated through the fatigue analysis via a commercial code, FEMFAT.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.121-121
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• 2009

자동차는 코너 주행 시 In-corner와 Out-corner 의 바퀴 궤적이 달라지므로, 특별한 장치가 없이 좌우 구동 측의 바퀴가 같은 속도로 회전을 하게 되면 정상적인 주행이 불가능하다. 따라서 정상적인 코너 주행이 가능 하려면, 코너 안쪽 바퀴보다 바깥쪽 바퀴가 더 빨리 회전해야 하며 이러한 회전 차를 보상받지 못할 경우 바깥쪽 바퀴가 끌리는 현상이 발생하는데 이를 방지하기 위해 디퍼렌셜 기어가 필요하다. 현재 디퍼렌셜 기어는 디퍼렌셜 케이스와 링기어를 볼트로 체결하는 조립 공법을 통해 생산되고 있다. 하지만 볼트 체결 공법은 조립을 위한 볼트와 볼트 체결을 위한 플랜지와 볼팅을 위한 홀을 가공하는 공정이 필요하기 때문에 재료비 절감 및 생산 효율 향상에 매우 불리하고 볼트체결을 위한 부분 때문에 불필요한 무게가 증가하게 된다. 따라서 본 연구에서는 이러한 기계적 체결 방식을 레이저 용접 방식으로 대체하여 재료비를 절감하고 무게 저감을 통해 주행성능을 향상시키고자 하였다. 링기어의 소재는 침탄처리강(SCM420H)이며 디퍼렌셜 케이스의 소재는 주철(GCD500)을 사용하고 있다. 주철은 용접시 용접부와 열영향부에서 마르텐사이트 조직과 레데브라이트, 시멘타이트 조직이 생성되며 고탄소 모재의 탄소 확산으로 인한 부분 혼합영역에서 탄소 합금이 생성되어 균열이 발생하는 등 용접성이 매우 좋지 않은 것으로 알려져 있다. 이러한 주철의 난용접성을 해결하는 방법으로는 고탄소 모재 용접시 발생하는 탄소의 확산을 억제하거나 예열이나 후열 처리를 통한 냉각 속도의 제어하는 방법과 오스테나이트 안정화 원소를 첨가한 필러와이어를 사용하여 용접시 마르텐사이트와 시멘타이트의 성장을 방해하는 방법 등이 이용되고 있다. 본 연구에서는 예열처리나 후열처리를 통한 주철의 용접법은 대량 생산을 통한 원가절감을 노리는 자동차 업계의 특성에 비추어 볼 때 비용이나 프로세스 구성 면에서 적용하는 것이 어려울 것이라 판단하여 Ni-base filler metal을 통한 주철의 용접법을 선택하였고 그 결과 실차에 적용하기 위한 비틀림 강성 테스트나 내구 테스트는 통과하였으나 NVH 테스트 결과 볼팅 체결 방식에 비하여 소음이 커지는 문제가 발생하고 링기어의 HAZ부가 고경화 되는 문제가 발생하였다. 때문에 용입깊이를 초기 시제품인 5mm에서 4mm로 변경시켜 입열량 감소 및 용접변형을 줄여 소음 문제를 해결하고자 하였으며 링기어의 침탄층을 1mm 절삭하여 링기어 HAZ부의 고경화 문제를 해결하고자 하였다. 이러한 용접 구조 변경이 용접변형 및 강성과 피로에 미치는 영향력을 알아보고자 용접 및 열처리 상용 소프트웨어인 SYSWELD, 구조해석 상용소프트웨어인 NX_NASTRAN, 피로 해석 상용 소프트웨어인 FEMFAT을 이용하여 시뮬레이션 하였고 실제 구조 변경한 용접 시제품과 비교, 분석하였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.1
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• pp.142-147
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• 2014

Finite element analysis along with DOE scheme has been performed to obtain robust design of connecting rod assembly. An analysis was conducted with five loading steps. Fatigue analysis was done using commercial software FEMFAT and fatigue safety factors at the interested regions such as shank area of small end and big end were calculated. 27 design cases using 3 factors with 3 levels are constructed by design of experiment. Each case is simulated to find the most influential factors. Response for this study, maximum Von-Mises stress, has been used to determine main factors of connecting rod assembly. Among the 3 factors, compression load affected the response greatly. However, bolt assembly load and width of shank flat area showed a little influence to the response. Interaction effects among factors considered did not occur. Connecting rod assembly considered in this study showed its sensitivity to the noise factor such as compression load rather than design factor such as width of flat shank area.