THERMAL CONTACT RESISTANCE AT THE INTERFACE OF DOUBLE TUBES ASSEMBLEDBY PLASTIC-DEFORMATION

An experimental investigation was carried out to study the behavior of thermal contact resistance (TCR) at the interface of metallic double tubes with respect to governing parameters. These parameters are: asse mbly pressure (contact pressure being inaccessible), temperature level (differential expansion), material characteristics and the presence o f grooves at the interface. All samples tested are industrial compound tubes assembled by a hydraulic packing technique (plastic deformation ) and have identical dimensions (thickness of each wall=1 mm and diame ter at the interface=13 mm). The experimental apparatus operates in a transient thermal regime. In this configuration the mechanical charact eristics of both partitions, in particular yield strength, Young modul us and ductility, have a decisive influence on the contact pressure. T he results show that, on a set of samples of the similar kind, the TCR presents a minimum value with increasing assembly pressure and temper ature level. This minimum value corresponds to the maximum interferenc e fit. The maximum interference fit value corresponds to the yield str ength of the outer tube when it is more ductile than the inner tube. O therwise, this maximum is reached when the slope of the constitutive l aw of the outer tube is inferior to the one of the inner tube. On a se t of samples of similar kind we have verified that thermal loading (di fferential expansion) gives the same result as the mechanical loading (internal pressure). It has also been observed that the presence of fo ur detection grooves (1/10 mm depth) at the interface, parallel to the tube axis, does not modify the optimum value of the TCR which is inst ead shifted towards lower assembly pressure values. (C) 1998 Elsevier Science Inc. All rights reserved.