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Lecture

Influence of type of loading and interference levels on the stress intensity factor for a crack emanating from a hole

Wednesday (27.05.2020)
16:40 - 17:00

Pin loaded lugs, rivet joints and bolted joints are indispensable elements of a structure in any industry. During service, these components undergo dynamic loading, resulting in fatigue failure. Several theoretical, experimental and numerical studies have been carried out to estimate stress intensity factors and fatigue lives in pin loaded lugs, rivet joints and bolted joints. Many of the previous studies do not address the combined effect of loading type and specimen geometry to arrive at SIF.

This study using Finite Element analysis, considers a rectangular plate with cracked hole to derive the stress intensity factor for a through-the-thickness crack for the following load cases: a) Direct loading- open hole configuration, b) Bearing load –cosine distribution, c) Pin load without interference, d) Pin load with various levels of interference with plate, e) Pin load with a bush interference with plate and no interference between pin and bush and f) Pin load with the size of pin equivalent to the bush.

Conclusions:

1) Irrespective of the type of loading, as the crack length increases, the SIF values converge up to 1% interference levels at 2a/W=0.73.

2) In case of pin load, for interference levels up to 0.5%, beyond 2a/W=0.33, there is no significant variation in the SIF values.

3) Beyond the threshold interference level of 0.5% between plate and pin, for all crack lengths, SIF increases with increase in interference levels.

4) Below the threshold interference limit, at each interference level, there exists a crack length beyond which the interference results in increase in SIF rather than reducing it.

5) The use of a bush along with pin is beneficial in reducing the SIF up to a transition value of 2a/W, ranging between 0.2 to 0.3. This is valid at all interference levels studied, except at 0.25% interference where, beyond 2a/W=0.33, there is no difference in SIF values between the two cases.

6) The pattern of variation of SIF is similar for both the cases of Bush interference and equivalent pin interference.

7) At lower interference levels, up to 0.25%, at all crack lengths, although bush interference yielded slightly higher SIF than the equivalent pin interference, at 0.5% level and higher levels, bush yielded lower SIF values compared to equivalent pin.

8) After certain crack length and certain interference levels, positive effects induced by interference are nullified by the geometrical effects.

Speaker:
Prof. Dr. Raghu Vasu Prakash
Indian Institute of Technology Madras
Additional Authors:
  • Karakampalle Hithedra
    Indian Institute of Technology Madras