Bolted joints design requirements

This behavior is particularly relevant with push-fit assemblies and bolted joints that rely on maintaining their load under constant strain. Special design features or analysis may be required to counteract excessive stress-relaxation. 

Analysis of a bolted repair follows the analysis of a bolted joint. The behaviour of composites in bolted joints differs considerably from what occurs with metals. The brittle nature of composites necessitates more detailed analysis to quantify the level of various stress peaks as stress concentrations. Composite joint design is more sensitive to edge distances and hole spacing than metal joint designs and requires specialised fasteners. Interference fit fasteners or rivets must not be used but expanding sleeves can be installed as required. 

Bickford, J. H. and S. Nassas. 1998. The Handbook of Bolts and Bolted Joints. New York Marcel Dekker. The design of bolted connections requires specialist knowledge that is frequently lacking in more general handbooks. 

The uncertainties highlighted by the variety of solutions adopted demonstrate the lack of a universally recognized method for the design of these joints which also satisfies the need for limiting the stresses in the flange and bolts, and the leak proofing requirements. The various standards are quoted in Section 14-3-5. 

Bonded joints are extensively employed in the construction of composite structures in aerospace applications, maritime structures, lifting equipment, wind mills as well as automotive industries [3, 4, 5], Unlike the bolt hole in mechanical fastening that causes a stress concentration in the composite joint plates, adhesively bonded joints minimize the potential for stress concentration within the joint. Besides, applications where lower structural weight, improved damage tolerance design philosophy are required, adhesively bonded joints provides a potential solution. Bonded joints are an efficent fastening solution also for hybrid structures, i.e., structures where composite parts are connected to metal parts. 

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