Sam-Hong Song

Fatigue Crack Propagation Behavior in STS304 Under Mixed-Mode Loading

The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failures occur from cracks subjected to mixed-mode loading. Hence, it is necessary to evaluate the fatigue behavior under mixed-mode loading. Under mixed-mode loading, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. In modified range 0.3≤a/W≤0.5, the stress intensity factors (SIFs) of mode I and mode II for the compact tension shear (CTS) specimen were calculated by using elastic finite element analysis. The propagation behavior of the fatigue cracks of cold rolled stainless steels (STS304) under mixed-mode conditions was evaluated by using KI and KII(SIFs of mode I and mode II). The maximum tangential stress (MTS) criterion and stress intensity factor were applied to predict the crack propagation direction and the propagation behavior of fatigue cracks.

Analysis of Delamination Behavior on the Stacking Sequence of Prosthetic Foot Keel in Glass fiber Reinforced Laminates

It is considered that the application of advanced composite materials to the prostheses for the disables is important to improve their bio-mechanical performance. Particularly, energy storing foot prosthesis is mostly important to restore gait ability of the disables with low-extremity amputation since it could provide propulsion at terminal stance enhancing the disables ability to walk long distance even run and jump. Therefore, the energy storing spring of Prosthetic foot keel under cyclic bending moment use mainly of high strength glass fiber reinforced plastic. The main objective of this study was to evaluate the stacking sequence effect using the delamination growth rate(dA/dN) of energy storing spring in glass fiber reinforced plastic under cyclic bending moment. The test results indicated that the shape of delamination zone depends on stacking sequence in GFRP laminates. Delamination area(A) turns out that variable types with the contour increased non-linearly toward the damage zones.nes.

Development of the Delamination Evaluation Parameters (I)-The Delamination Aspect Ratio and the Delamination Shape Factors-

Although the previous researches evaluated the fatigue behavior of A1/GFRP laminates using the traditional fracture mechanism, their researches were not sufficient to do it : the damage zone of A1/GFRP laminates was occurred at the delamination zone instead of the crack-metallic damages. Thus, previous researches were not applicable to the fatigue behavior of Al/GFRP laminates. The major purpose of this study was to evaluate delamination behavior using the relationship between crack length(a) and delamination width(b) in A1/GFRP laminate. The details of investigation were as follows : 1) Relationship between the crack length(a) and the delamination width(b), 2) Relationship between the delamination aspect ratio(b/a) and the delamination area rate ( (Ad)n/ (Ad) all) , 3) The effect of delamination aspect ratio(b/a) on the delamination shape factor (fs) and the delamination growth rate (dAd/da). As results, it was known that the delamination aspect ratio(b/a) was decreased and the delamination area rate ( (Ad)n/ (Ad)All) was increased as the normalized crack size(a/W) was increased. And, the delamination shape factors (fs) of the ellipse-II (fs3) was greater than of the ellipse-1 (fs2) but that of the triangle (fs1) was less than of the ellipse-I (fs2).

Stress Distribution and Crack Initiation Behavior due to the Defect Locations in Monolithic Aluminum and Al/Glass Fiber Laminates

Material flaws in the from of pre-existing defects can severely affect the crack initiation. Stress distribution and crack initiation life of engineering materials such as monolithic aluminum alloy and Al/Glass fiber laminate may be different according to the defect location. The aim of this study is to evaluate effects of relative location of defects around the circular hole in monolithic aluminum and Al/Glass fiber laminates under cyclic bending moment. Stress distribution and crack initiation behavior near a circular hole are considered. Results of Finite Element (FE) model indicated the features of different stress field due to the relative defects positions. Especially, the defects positions at

The Damage Behavior of Glass/Epoxy and Aramid/Epoxy in Leaf Spring of Ankle Foot Orthosis (A.F.O) due to the Various Impact Velocities

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The Effect of Fiber Stacking Angle on the Relationship Between Fatigue Crack and Delamination Behavior in a Hybrid Composite Materials

The needs of walking assistant device such as the Ankle Foot Orthosis (A.F.O) are getting greater than before. However, most of the A.F.O are generally imported rather than domestic manufacturing. The major reason of high import reliability is the rack of impact properties of domestic commercial products. Therefore, this research is going to focus on the evaluation of impact properties of the A.F.O which has the high import reliability. Unfortunately, these kinds of researches are not performed sufficiently. This research is going to evaluate impact energy behavior in composite materials such as the glass/epoxy (S-glass, [0/90]sub 2S/) and the aramid/epoxy (Kevlar-29, woven type, 8 ply) of ankle foot orthosis. The approach methods were as follows. 1) The history of impact load and impact energy due to the various velocities. 2) Relationship between the deflection and damage shape according to the impact velocities. 3) The behavior of absorbed energy and residual strength rate due to the various impact velocities.

Evaluation of Delamination for Fiber Reinforced Metal Laminates Using a Pseudo Crack Model

The hybrid composite material (Al/GFRP laminates) are applied to the fuselage and wing in a aircraft. Therefore, Al/GFRP laminates suffer from the cyclic bending moments. This study was to evaluate the effect of fiber stacking angle on the fatigue crack propagation and delamination behavior using the relationship between crack growth rate (da/dN) and stress intensity factor range (ΔK) in Al/GFRP laminates under cyclic bending moment. The variable delamination growth behavior in case of three different type of fiber orientations, i.e., [Al/O/Al], [Al/+45/Al] and [Al/90/Al] at the interface of Al layer and glass fiber layer was measured by ultrasonic C-scan images. As results of this study, It represent that the delamination shape should turns out to have more effective characteristics on the fiber stacking angle. The extension of the delamination zone in case of [Al/+45/Al] and [Al/90/Al] were not formed along the fatigue crack profile. The shape of delamination zone depend on fiber stacking angle and the variable type with the delamination contour decreased non-linearly toward the crack tip at the Al layer.

Evaluation of Fatigue Delamination Behavior in Hybrid Composite Material Using the Delamination Shape Parameters

If Fiber Reinforced Metal Laminates(FRMLs) were delaminated, the decrease of stiffness and fiber bridging effect would result in the sudden aggravation of fatigue characteristics. It was reported that the delamination of FRMLs resulted from the crack of metal layers and that it depended on the crack growth. While cracks were made in FRMLs containing a saw-cuts under fatigue loading, cracks could be produced or not in FRMLs with circular holes under the same condition. When the FRMLs with the circular holes produce not the crack but the delamination, it is not possible to analyze it by the conventional fracture parameters expressed as the function of the crack. And so, this research suggests a new analytical model of the delamination to make the comparison of the delamination behavior possible whenever the cracks occur or not. Therefore, a new analytical model called Pseudo Crack Model(PCM) was suggested to compare the delaminations whether cracks were made or not. The relationship between the crack energy consumption rate( ) and the delamination energy consumption rate( ) was discussed and it was also known that the effect of was larger than that of .

An Experimental Study on the Fatigue Crack Propagation Behavior in CTS Specimen under Mode II Loading

The applicability of the hybrid composite materials such as AlIGFRP laminates is restricted due to the frequent delamination of different materials at interlaminar. The previous researches showed that the major parameter to control the delamination of AI/GFRP laminates was a crack ( a ). On the other hand, it was also shown that a delamination width ( b ) could strongly effect on the delamination behavior. Therefore, the aim ofthis research is to define the delamination behavior using the above correlation. We obtained result as follow. The delamination aspect ratio ( b/a ) that was suggested from the increasing a-b relationship was decreased with increasing of a/W . The suggested the delamination area rate (( AD ) N /( AD ) All ) which represented the growth rate of delamination area ( AD ), was going higher while a/W was increasing.

The Analysis of Fatigue Behavior Using the Delamination Growth Rate(dA D /da) and Fiber Bridging Effect Factor(F BE ) in Al/GERP Laminates

The purpose of this paper is to investigate fatigue crack behavior under shear(Mode II) loading. Various specimens and devices have been used in order to produce Mode II loading in fatigue experiments for shear crack propagation. But, there is not sufficient comparisons of experimental results between Mode II and others loading modes, because of characteristics of applied loads and specimens. So, compact tension shear(CTS) specimens were used in this paper to investigate the propagation behavior of Mode II by comparing the experimental results between loading modes. We firstly observed the characteristics which was showed in Mode II experiment using CTS specimens. The experimental results under Mode II loading were compared with fatigue crack behavior under Mode I and Mixed-mode I＋II loading. The characteristics for initiation and propagation behavior under Mode II loading was investigated by such comparisons.