Experimental validation of a model forT-bolt mechanical joints

摘要

T-bolts are widely used for joining thick laminates, especially at the root of large windturbine blades, because of its good reproducibility and a lower cost than other joining procedures.T-bolts are quite common for joining wood and wood-agglomerates; a transverse cylinder receives theload from the laminate and transfers it to a tension bolt, located in a hole done in the plane of thelaminate. A high pretension is introduced at the bolts in order to assure the joint and for alleviating thefatigue on these bolts. This pretension introduces a compressive strain state in the laminate; therefore,classical failure analysis of mechanical joints must be modified to take it into account, becausebearing failures are predominant, due to both, a reduced bearing surface and a more complex stressstate compared to typical mechanical joints.This paper describes the constitution and function of the different components of the joint, showingthe different parameters that affect its performance, and presents a parametric analysis, useful for jointdesign and optimization, relating laminate thickness, bolt and cylinder diameters with pitch distance,and pretension of the bolt with external load. In order to provide information on the influence of theT-bolt geometry on the strength of the laminate in the net tension and bearing zones, tests for twodifferent glass fiber - epoxy laminates, under different pitch/diameter ratios have been done, forcingeither bearing or tension failure modes. Stress and strain concentrations in the laminate have beenestimated trough a three-dimensional finite element model that takes into account pretension effectsand contact nonlinearities. How experimental results correlate with simple and finite element modelanalysis is discussed, and some conclusions are drawn.