Fillets design factors

The report of the inquiry [111] criticised the design and fabrication of the alterations made to the original pontoon. The actual cause of the accident was the failure of some tie bars in the detail around the jacking points. The failure was due to brittle fracture which initiated from severe notches such as a small radius curve at the fillet between the spade end and the shank of the tie bar. Weld defects and fatigue cracks were also present in tie bars subsequently recovered from the sea bed. The tie bars had been flame cut to shape and had weld repairs visible to the eye. There had been no post welding heat treatment of the steel. The steel complied with the original specification but tests showed low Charpy V notch impact values. Photo elastic tests indicated a stress concentration factor of 7 at the fillet between the spade end and the shank. The fracture was initiated in the opinion of the inquiry tribunal by the low ambient temperature of around 3°C. 

Thickness of the adhesive is varied to suit the specific application. For example, when the substrates to be bonded are smooth and uniform in thickness a light weight adhesive of about 5 mils in thickness is usually selected. For assemblies having large or variable gaps, adhesives up to 15 mils or higher in thickness are utilized. Examination of the honeycomb panel pictured in Fig. 1 makes it obvious that adhesive thickness is a critical factor that must be considered in the design of sandwich structure. The size of the adhesive fillets and thickness of the face bond adhesive determine the... 

Each of these factors is discussed next and detailed design guidelines are given. The residual stresses caused by thermal effects are also discussed. Note that the joint strength can be further improved by using adhesive fillets, adherend tapers, and adhesive bands along the overlap or hybrid joints. These solutions are described in Sect. 27.3. 

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