• Journal of Mechanical Science and Technology
• /
• 제17권3호
• /
• pp.343-349
• /
• 2003

The fuselage-wing intersection suffers from the cyclic bending moment of variable amplitude. Therefore, the influence of cyclic bending moment on the delamination and the fatigue crack propagation behavior in AFRP/Al laminate of fuselage-wing was investigated in this study. The cyclic bending moment fatigue test in AFRP/Al laminate was performed with five levels of bending moment. The shape and size of the delamination Lone formed along the fatigue crack between aluminum sheet and aramid fiber-adhesive layer were measured by an ultrasonic C-scan. The relationships between da/dN and ΔK, between the cyclic bending moment and the delamination zone size, and between the fiber bridging behavior and the delamination zone were studied. As results, fiber failures were not observed in the delamination zone in this study, the fiber bridging modification factor increases and the fatigue crack growth rate decrease and the shape of delamination zone is semi-elliptic with the contour decreasing non-linearly toward the crack tip.

• 한국생산제조학회지
• /
• 제18권4호
• /
• pp.362-368
• /
• 2009

In general, circuit board assemblies experience various mechanical loadings during assembly and in actual use. The repeated cyclic bending can cause electrical failures due to circuit board cracks, solder interconnects cracks, and the component cracks. In this paper, we report on the failure characteristics of semiconductor chips under the repeated cyclic bending. We first describe a new 4-point bending tester, which is developed according to JEDEC standard No. 22B113. The performance of the tester is then estimated through actual experiments. Test results reveal that the cracks first occur on the outer balls around 20,000 cycles and gradually propagate to the inner balls where cracks are found around 70,000 cycles.

• 소성∙가공
• /
• 제26권1호
• /
• pp.41-47
• /
• 2017

Cyclic behavior of advanced high strength steel sheets was measured using an inverse-optimization approach with pre-straining and bending. First, tensile specimens were pre-strained, and three-point bending was conducted for the pre-strained specimens. By using the inverse finite element optimization, the combined isotropic-kinematic hardening parameters that minimize the error between the measured and predicted bending force-displacement curves. The measured cyclic behavior agreed well with the cyclic behavior measured by sheet tension-compression test, which confirms the validity of the measuring procedure based on inverse optimization.

• Structural Engineering and Mechanics
• /
• 제11권3호
• /
• pp.315-324
• /
• 2001

This paper presents the experimetal result on the viscoplastic response and collapse of the titanium alloy tubes subjected to cyclic bending. Based on the capacity of the bending machine, three different curvature-rates were used to highlight the viscoplastic behavior of the titanium alloy tubes. The Curvature-controlled experiments were conducted by the curvature-ovalization measurement apparatus which was designed by Pan et al. (1998). It can be observed from experimental data that the higher the applied curvature-rate, the greater is the degree of hardening of titanium alloy tube. However, the higher the applied curvature-rate, the greater is the degree of ovalization of tube cross-section. Furthermore, due to the greater degree of the ovalization of tube cross-section for higher curvature-rates under cyclic bending, the number of cycles to produce buckling is correspondingly reduced. Finally, the theoretical formulation, proposed by Pan and Her (1998), was modified so that it can be used for simulating the relationship between the controlled curvature and the number of cycles to produce buckling for titanium alloy tubes under cyclic bending with different curvature-rates. The theoretical simulation was compared with the experimental test data. Good agreement between the experimental and theoretical results has been achieved.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.1740-1743
• /
• 2007

In this study, two types of fatigue tests were conducted. First, cyclic bending tests were performed using the micro-bending tester. A four-point bending test method was adopted, because it induces uniform stress fields within a loading span. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. The pseudo-power cycling method makes up for the weak points in a power cycling and a chamber cycling method. Two compositions of solder are tested in all test condition, one is lead-free solder (95.5Sn4.0Ag0.5Cu) and the other is eutectic lead-contained solder (63Sn37Pb). In the cyclic bending test, the solder that exhibits a good reliability can be reversed depending on the load conditions. The lead-contained solders have a longer fatigue life in the region where the applied load is high. On the contrary, the lead-free solder sustained more cyclic loads in the small load region. A similar trend was detected at the thermal cycling test. A three-dimensional finite element analysis model was constructed. A finite element analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. A constitutive model which includes both creep and plasticity was employed. Thermal fatigue was occurred due to the creep. And plastic deformation is main damage for bending failure. From the inelastic energy dissipation per cycle versus fatigue life curve, it can be found that the bending fatigue life is longer than the thermal fatigue life.

• 한국압력기기공학회 논문집
• /
• 제18권2호
• /
• pp.77-86
• /
• 2022

This study investigates the effect of the diameter and thickness on crack initiation location and orientation of 90° elbows under in-plane mode displacement-controlled cyclic bending loads. Finite element (FE) analysis of cyclic failure test is conducted for elbow specimens under in-plane mode displacement-controlled cyclic bending to identify the parameters affecting crack location and orientation. Furthermore, parametric FE analysis of the pipe elbows with various pipe nominal sizes and Schedules is performed, and the crack location and orientation from the results of FE analysis are determined. It is found that the crack location and orientation in the pipe elbows are determined mianly by the radius to thickness ratio of pipe elbows (R_m/t). It is also found that the presence of internal pressure slightly increases the value of R_m/t at which the failure mode changes.

• Steel and Composite Structures
• /
• 제39권3호
• /
• pp.229-241
• /
• 2021

This work focused on aluminum foam sandwich (AFS) with different foam core densities and different face-sheet thicknesses subjected to constant amplitude three-point bending cyclic loading to study its fatigue performance. The experiments were conducted out by a high frequency fatigue test machine named GPS-100. The experimental results showed that the fatigue life of AFS decreased with the increasing loading level and the structure was sensitive to cyclic loading, especially when the loading level was under 20%. S-N curves of nine groups of AFS specimens were obtained and the fatigue life of AFS followed three-parameter lognormal distribution well. AFS under low cyclic loading showed pronounced cyclic hardening and the static strength after fatigue test increased. For the same loading level, effects of foam core density and face-sheet thickness on the fatigue life of AFS structure were trade-off and for the same loading value, the fatigue life of AFS increased with aluminum foam core density or face-sheet thickness monotonously. Core shear was the main failure mode in the present study.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집A
• /
• pp.231-237
• /
• 2000

A15052/AFRP laminates were developed principally to obtain a material with good fatigue strength, in which possible cracks would grow very slowly. Weight savings of more than 30% should be attainable in practice. Also, the crack bridging fibers could still was carry a significant part of the load over the crack, thus the COD and stress intensity factor was reduced at the crack tip. A15052/ AFRP laminates consists of three thin sheets of 5052-H34 aluminum alloy and two layers of [0] unidirectional aramid fiber prepreg. The cyclic-bending moment test was investigated based on applying the five kinds of bending moments. The size of the delamination zone produced between 5052-H34 aluminum alloy sheets and fiber-adhesive layers was measured from ultrasonic C-scan pictures taken around the fatigue crack. In addition, the relationship between the cyclic-bending moment and the delamination zone size was studied and the effect of fiber bridging mechanism was also considered.

• 국제강구조저널
• /
• 제18권5호
• /
• pp.1772-1783
• /
• 2018

Nowadays, the researches about composite structure system are being implemented in various fields, and many steel structures are designed based on that. In this study, the bending and seismic performance of the newly developed high-performance cold forming composite beam are evaluated by several experiments. As a result of the bending performance test, the bending moment of beam was increased stably depending on the depth and plate thickness of beam, and it is considered that the bending moment can be evaluated by the equation of a composite beam design. As a result of the seismic performance test, it was verified that sufficient seismic performance was obtained despite the increase of a negative moment rebar and depth of beam. In addition, the nominal bending moment has obtained the strength above the plastic bending moment, and also the plastic rotation angle has satisfied the requirement of composite intermediate moment frame.

• 한국지반공학회논문집
• /
• 제26권12호
• /
• pp.41-50
• /
• 2010

반복수평하중을 받는 말뚝의 거동은 정적하중을 받는 경우와 다르며, 지반 및 하중특성에 영향을 받는다. 본 연구에서는 모래지반에서 반복하중특성이 말뚝의 수평거동에 미치는 영향을 조사하기 위하여 가압토조를 이용한 모형말뚝 재하시험을 수행하였다. 실험결과에 따르면 반복수평하중을 받는 말뚝의 극한수평지지력은 하중의 반복재하횟수가 많아질수록 선형적으로 감소하였고 수평하중의 크기가 커질수록 조금씩 증가하였다. 그리고 수평하중의 반복재하횟수가 증가할수록 극한상태에서 말뚝에 발생하는 최대 휨모멘트는 감소했으나 그 발생위치는 말뚝 근입길이의 0.36배 되는 곳으로 일정하였다. 반면 반복수평하중의 크기가 증가하면 극한상태에서 말뚝의 최대 휨모멘트와 그 발생위치가 조금씩 증가하였으며, 반복수평하중은 정적하중에 비해 말뚝의 극한수평지지력과 극한상태에서 말뚝의 최대 휨모멘트를 감소시키는 것으로 나타났다. 또한 모형실험결과에 근거해서 조밀한 모래지반에서 반복수평하중을 받는 말뚝의 극한수평지지력을 산정할 수 있는 지지력산정식을 제안하였으며, 제안식으로부터 얻은 계산치를 실험치와 비교한 결과 제안식은 모형실험의 결과를 잘 반영하는 것으로 나타났다.