Axial Clamping Behaviour of V-band clamps at Ambient and High temperature

V-band clamps provide an efficient method of fastening pairs of tubular shaped bodies. Their applications are widely seen in connecting tubes, hoses, ducts, pumps, turbochargers, exhaust systems. As well as providing a robust connection at the exhaust end of the engine, a V-band clamp must generate enough axial clamping load to prevent leakage at the joint. It must do this whilst being subjected to severe thermal cycling, in addition to the mechanical loads. The existing theoretical models of V-band clamps show a weak experimental correlation for low aspect ratio V-clamps, where the ratio of diameter to the profile depth is small. Also, there has been no allowance for thermal loading. In addition to the total clamping force, the existing theory predicts an exponential drop in the clamping force around the circumference. However, there has been no experimental data to validate such behaviour for load distribution.

This project investigates the clamping behaviour of low aspect ratio V-clamps operating at ambient and high temperature. The typical diameter range for these clamps lies in between 50 mm to 150 mm. A theoretical model was developed accounting for non-conformance of the clamp and flange, allowing the axial clamping load to be determined as a function of screw force. The analytical results showed that due to the large ring stiffness and non-conforming nature of the geometry, the axial clamping load generated by these clamps is dependent on the flange diameter, where an increase in diameter increases the clamping force. For the empirical study, two state of the art test rigs were designed and manufactured. Both test rigs utilized strain gauges to measure the clamping force distribution in 30° increments around the circumference. A highly non-uniform load distribution was measured for these clamps, where the highest load was recorded at the hardware and at the bridge end of the clamp. At moderate screw forces the correlation between theory and experimental results was good. However at large screw force and due to the head touching design feature of the tested clamps, the comparability between the experimental and theoretical results was limited.

To predict the effect of thermal loading on the clamping behaviour of the V-band, a novel theoretical model was developed. This analytical model utilises the theory of partially plastic behaviour of material under temperature. The analytical results predicted up to 69% drop in clamping force at 700°C skin temperature. These results were compared with the experimental results, where a novel test methodology was developed that utilises the use of high temperature strain gauges for load measurement. The experimental results for all tests exhibited reduction in clamping force and screw force. At 700°C the clamp showed a reduction of 61% in clamping force and over 50% drop in the screw force, which was also monitored during the tests.