An experimental investigation of thermal contact conductance across bolted joints

An experimental study of thermal contact conductance was conducted with pairs of aluminum alloy (6061-T6) specimens jointed by bolts. The individual aluminum samples have a square cross-section (63.5 turn x 63.5 mm) and a height of 50 mm. Three different bolt patterns were adopted in this study, including single-bolt, 4-bolt, and 8-bolt configurations. The bolt-shaft diameters were 3, 5, and 8 mm, and the torque applied on each bolt was between 1 and 10 N m. The heat flux through the test specimens ranged from 4 to 20 kW/m(2). The interfacial contact pressure of bolt-jointed specimens was determined by a pressure-measuring film inserted between samples. Results show that the interfacial contact pressure increases with an increase of either the applied torque or the number of bolts. The interfacial temperature difference across the junction was substantially reduced for bolt-jointed specimens, when compared with two superimposed samples without bolts. With the same bolt number, the variation of bolt-shaft diameter from 5 to 8 mm yields nearly no influence on the thermal contact conductance. However, when the size of bolt was kept constant the thermal contact conductance of samples jointed by 8 bolts was greatly larger than that of 4-bolt samples. The increase of contact surface roughness of test specimens leads to a decrease of the thermal contact conductance. When an RTV silicon layer was used as the interstitial material, the total joint conductance of Al/RTV/Al was much lower than the contact conductance of bare aluminum contact. The total joint conductance of Al/RTV/Al was increased with a decrease of the thickness of RTV silicon layers. (C) 2001 Elsevier Science Inc. All rights reserved.