The tearing behaviour and effect of laundering on knicker fabrics

Abstract

Fabrics are frequently used in forensic examinations. Without textile knowledge of fabrics it is easy to assume that all fabrics are the same when they in fact they are different. The most frequent clothing damage in forensic investigations is caused by ripping/tearing; cutting with scissors; slashing, or stabbing with a knife; and from the discharge of a firearm. Each mode of damage to fabric produces its own pattern, resulting from the manner in which the damage was inflicted and the properties of the fabric involved. Very few investigations of tearing damage have been identified, and those which have been published, lack details of test methods or conditions, therefore do not consider the highly variable nature of apparel fabrics. Apparel evidence collected at crime scenes is likely to have been worn and laundered multiple times prior to the event. Hence, from a forensic perspective it is important to understand how laundering affects the behaviour of fabrics and any damage produced in the commission of a crime (e.g. tearing, stabbing). This study compares selected fabric and tear-related properties of three knicker fabrics and investigates the effect of laundering on tearing behaviour.

A factorial experimental design and standard test methods relevant to apparel were used to control as many variables as possible. Three knit fabrics, typical of those used to manufacture knickers sold in New Zealand, were selected to be as similar as possible with the exception of fibre content. Three levels of laundering were selected (0, 6 and 60 cycles); fabrics were laundered prior to testing. A standard test method for woven fabrics was adapted as no standard method for tearing knitted fabrics was identified.

Fibre content was the most influential factor. Cotton and cotton rich fabrics have a greater tear force, therefore, they are more difficult to tear. Adding elastane to fabrics increases the time it takes for the tear to initiate as the elastane fibres allow the fabric to extend more before breaking. Specimens behaved differently depending on which direction they were being torn. Tearing behaviour was affected by fibre content and the level of laundering prior to tearing. Tearing can occur in both the wale and course direction but only under given circumstances. Fabrics which have been laundered require less force to tear than new fabrics due to fibre/yarn/fabric damage. SEM provided a useful visual tool for fabrics and fibres subjected to tearing. The torn cotton fabric had fibres with ends similar to those damaged by a screwdriver and torn elastane fibres had clean cut fibre ends which could be mistaken for knife damage. No features visible under SEM could be attributed solely to tearing damage in the fabrics studied.

Caution should be exercised when using fibre end morphology to identify tearing damage. Tests in this study were conducted on fabrics not garments. Thus, results from this study may not be appropriate to apply to garments, particularly if a garment fails at the seams rather than any other way.

The current work is intended to establish a base line, which may be applied to knicker fabrics as forensic textile evidence and provide a reference for further study.