PSI - Issue 19

Yoichi Yamashita et al. / Procedia Structural Integrity 19 (2019) 123–129 Yamashita et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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One of the easiest and most accessible crack arresting methods is drilling hole close to the crack tip. This stop - hole technique is often used to diminish the stress concentration at the crack tip and to increase the fatigue strength or the fatigue failure life of infrastructure (Ayatollahi et al. (2014)). In this study “ crack growth arrest and retardation system” u sing “ gourd-shaped-insert-plate ” has been developed as a high performance and easy construction method against fatigue crack, by using the arrester to close fatigue crack and reduce crack tip opening displacement and stress concentration at the fatigue crack tip. Arrester was applied to CT (Compact Tension) specimen and also mockup of steel bridge deck, in order to validate performance of the system. In the fatigue crack growth tests using CT specimens, fatigue crack growth rates of the specimens with arrester were 1/10 ~ 1/2 of those without arrester. And apparent threshold stress intensity factor range was increased by about 10~20 MPa√ through using only few gourd-shaped arresters. Also, the arrester was applied to the fatigue crack in a mockup of steel bridge deck. Without arrester, fatigue crack growth occurred in accordance with the increase of loading cycles. On the other hand, fatigue crack growth was arrested after application of the arrester in the mockup of steel bridge deck. And to enable quantitative fatigue life assessment in fatigue design, fracture mechanics based-crack closure model with spring elements for the arrester has been verified with good accuracy for fatigue crack growth rate in the tests using CT specimens. Nomenclature ∆ Stress intensity factor range ∆ Apparent stress intensity factor range ∆ Load range in compact tension specimen Plate thickness of specimen Width of specimen Crack length of specimen Crack length ratio to width, a/W 2. Principe of fatigue crack growth arrester with “ Gourd-Shaped-Insert-Plate ” 2.1. Shape of Crack arrester and application to through-thickness plate For a growing fatigue crack, a gourd-shaped inset plate has been adopted as the crack arrester to suppress the crack tip opening displacement as shown in Fig. 1. Performance of fatigue crack growth depends on the number of insert plates and installed locations.

2.2. Construction process

First the gourd-shaped-through-thickness hole is drilled by electro-discharge machining system (EDM) or wire cutting. Then gourd-shaped pieces are inserted with adhesive bonding for metals. In this process the gourd-shaped insert-plate is fixed and locked with structural adhesive, PLEXUS AO420 (ITW Performance Polymers).

2.3. Principle of crack arrest

Generally fatigue crack grows due to crack opening displacement under cyclic loading. After setting up the gourd-shaped-insert-plate, the insert plate is locked behind the crack tip and constraint force is generated against crack opening by being caught to the arrester. This constraint has a role of crack closure force as a line-spring element on crack faces when the crack is opening. This spring system of gourd-shaped-insert-plate and soft structural adhesive is effective to crack arrest and crack growth rate retardation.