Page 184 - Failure Analysis Case Studies II

Failure Analysis Case Studies 11
D.R.H. Jones (Editor)
0 2001 Elsevier Science Ltd. All rights reserved 169

Premature fracture of a composite nylon radiator

P.R. Lewis*
Department of Muteriab Engineering, Faculty of Technology, The Open University, Walton Hull,
Milton Keynes MK7 6AA, U.K.

Received 30 August 1998; accepted 8 September 1998

Abstract

Fracture of a GF nylon composite radiator occurred in a new car, leading to seizure of the engine. The
fracture probably started at a cold slug or void present on an unusually large weld line in the radiator, itself
probably created by poor moulding conditions. Rather than being a design fault, the failure was probably
caused by lack of quality control during injection moulding. 0 1999 Elsevier Science Ltd. All rights reserved.

Keywords: Radiator; Nylon; Composite; Void; Weld line; Fracture

1. Introduction

A new design of radiator tank failed on a new car during test driving. The tank was constructed
from glass-filled (GF) nylon, a composite material used in engine compartments for its temperature
resistance and strength. Many inlet manifolds, such as that on the new Jaguar XK8 for example,
are now made from GF nylon 6,6 using the lost-metal injection moulding process [ 11.
The car had only travelled about 500 miles before catastrophic failure of the cooling system,
which led to seizure of the engine. Some 200 similar prototype tanks had been produced and fitted
to similar cars, and the manufacturer was concerned that there might be a design problem.
Although they had considerable experience with the material in other radiators, the bodies were
moulded by a sub-contractor elsewhere.
They therefore wished to know how the crack had been formed in the radiator, and whether the
problem was due to faulty material, poor design or manufacture, or a combination of such causes.
A programme of microscopy was undertaken to examine the fracture surface and other features
of the moulded tank. A new, unused tank was used for comparison. Mechanical testing was also
used to examine the quality of the material.

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Reprinted from Engineering Failure Analysis 6 (3), 1 8 1 - 195 (1 999)