Composite-to-metal tubular lap joints: strength and fatigue resistance

Abstract

The axial strength and fatigue resistance of thick-walled, adhesively bonded E-glass composite-to-aluminum tubular lap joints have been measured for tensile and compressive loadings. The joint specimen bonds a 63 mm OD aluminium tube within each end of a 300mm long, 6mm thick E-glass/epoxy tube. Untapered, 12.5mm thick aluminium adherends were used in all but four of the joint specimens. The aluminum adherends in the remaining four specimens were tapered to a thickness of 1 mm at the inner bond end (the bond end where the aluminum adherend terminates). For all loadings, joint failure initiates at the inner bond end as a crack grows in the adhesive adjacent to the interface. Test results for a tension-tension fatigue loading indicate that fatigue can severely degrade joint performance. Interestingly, measured tensile strength and fatigue resistance for joints with untapered adherends is substantially greater than compressive strength and fatigue resistance.The joint specimen has been analyzed in two different ways: one approach models the adhesive as an uncracked, elastic-perfectly plastic material, while the other approach uses a linear elastic fracture mechanics methodology. Results for the uncracked, elastic-plastic adhesive model indicate that observed bond failure occurs in the region of highest calculated stresses, extensive bond yielding occurs at load levels well below that required to fail the joint, and a tensile peel stress is generated by a compressive joint loading when the aluminum adherends are untapered. This latter result is consistent with the observed joint tensile-compressive strength differential. Results of the linear elastic fracture mechanics analysis of a joint with untapered aluminum adherends are also consistent with the observed differential strength effect since a mode I crack loading is predicted for a compressive joint loading. Calculations and a limited number of tests suggest that it may be possible to selectively control the differential strength effect by tapering the aluminum adherends. The effect of adherend material and thickness on fracture mechanics parameters is also investigated. The paper concludes by examining the applicability of linear elastic fracture mechanics to the joints tested.

On the Fatigue Analysis of Wind Turbines

“…"However, for ourdiscussions here,this solutionis adequate. In a series of papers, MetZinger et al [197][198][199][200][201][202][203] have combined state-of-the-art finite element analysis (FEA) techniques with experimental vdldation to examine idealized tubular lap joints that approximately represent the root connections in wind turbine blades. The joints that they analyzed, for the most part, are metallic (aluminum or steel) cylinders bonded to a fiberglass cylinder.…”

“…To analyze this joing detailed finite element analyses of the joint were first conducted for axial loads using two-dimensional (2D) axisyrnmetric meshes [198]. In two of the analyses presented in that paper, the adhesive is characterized as an unflawed (untracked), elastic-plastic material and, in the another analysis, an elastic fi-acture mechanics methodology is used.…”

“…Tapered Adherents: A common technique for reducing the stress risers at the ends of the bond joint is tapering the adherents to eliminate [198] and Metzinger and Guess [202], the results are inconclusive because of the limited number of specimens tested and because no attempts were made to optimize the taper. However, these first look results do indicate that for this geometry, tapering the adherents will probably be a second order effect to the sign of the peel stresses (see the "Peel Stress" discussion in section 8.2.2.3 "Geometric Considerations" on p. 95).…”

Stress and damage analysis of composite–aluminium joints used in electrical insulators subject to traction and bending

“…Experimental studies have compared the bonded, bolted and bonded-bolted composite-metal joints and evaluated the properties of different joints on the phenomenological level [2,5,6]. Experimental and to a lesser extent analytical works have also been reported on the fatigue behaviour of composite-metal joints under cyclic loads [7][8][9][10][11] and more recently on the failure behaviour under thermo-mechanical loads [12]. Numerical investigations on this subject are however practically nonexistent, except of a few studies on bonded tubular composite-metal joints under hydrostatic pressure or axial and bending loadings [13,14].…”

Treatment of Unsymmetric Adhesively Bonded Composite Sandwich Panels-To-Flange Joints

“…Based on a beam-column approach pioneered by Goland and Reissner [2], Lai et al [27] also developed a close-form solution for the single-lap joints with three different boundary conditions. Reedy and Guess [28] conducted an experimental investigation to study the axial strength and fatigue resistance of thick-walled adhesively bonded E-glass composite-to-aluminum single-lap joints. An experimental and numerical study was also conducted to investigate the postbuckling induced failure in adhesively bonded composite panel-to-flange joints by Tong et al [29].…”