Multi-fastener Joints Research Articles

PPARATUS FOR BEARING-BYPASS TESTING OF BOLTED JOINTS

A dual-control test system measuring the strength of graphite/epoxy specimens under tension and compression for a wide range of bearing-bypass load ratios is presented. The bearing-bypass strengths of single-fastener specimens are measured for damage onset and ultimate failure and are plotted against one another. The results indicate that an initiated damage grows to failure in the same mode for most cases. However, if the damage is initiated in the compression-reacted-bearing mode, the specimens fail in the offset-compression mode. It is concluded that this type of transition can occur in multi-fastener joints under compression and complicate the strength predictions. 12 refs.

Steam generator tube integrity program phase II final report : 39497 Kurtz, R.J.; Bickford, R.L.; Clark, R.A.; Morris, C.J.; Simonen, F.A.; Wheeler, K.R. U.S. Nuclear Regulatory Commission, Washington, D.C. (United States), NUREG/CR-2336, 100 pp. (Aug. 1988)

In an assembled aircraft structure, bolts or rivets are widely used as multifastener joints. They are sometimes the weakest component of a structure due to the high intensity of joint load. Earlier studies were focused on developing analytical and numerical methods for stress and failure predictions of multifastener joints. Typical models concerned panels joined by single or multiple joints, in which joint loads as well as stress distributions around pin holes, etc., are mostly analyzed. Poon and Xiong and Oh et al. considered the optimization of fastener joint locations, ply angles and stacking sequences of laminates, fastener diameters and edge distances, etc., to avoid the failure of fasteners. Bianchi et al. developed an optimization procedure maximizing the load-carrying capability of the joint system to balance the number and size of bolts. Ekh and Schön evaluated the effects of different parameters on the load distribution, such as the mismatch of member plates, length of the overlap region and the fastener’s stiffness. Optimization was then carried out to minimize the bearing stress. In the work of Oinonen et al. a “weakest link” method was proposed to optimize the layout of fasteners for the bracket-to-beam joints. The design objective was to ameliorate Von-Mises equivalent strain as well as shear loads in the joints.

The development of mode I, linear-elastic stress intensity factor solutions for cracks in mechanically fastened joints

Accurate representation of crack tip stress intensity is an essential part of the assessment of the damage tolerance capability of aerospace structures. In typical applications, mode I stress intensity solutions are taken as factorial combinations of the fundamental form and various boundary correction factors for any given geometry and applied load. Total solutions are then developed by superimposing individual solutions for various load conditions. This technique is discussed for typical structure involving loaded fastener holes. Tabulated and plotted results are presented for cracks emanating from both open and loaded holes in finite width plates, lugs and multi-fastener joints. In the case of the open hole and lug solutions, the results are compared with published finite element values. The expressions presented herein lend themselves to programming on a digital computer. Once established, they afford the engineer the ability to develop accurate K I solutions for a wide range of applications which are typical of the geometry/loading configurations encountered in the damage tolerance analysis of mechanically fastened joints. Equally as important, they offer accuracy comparable to that obtained with finite element modeling at a fraction of the cost.