LAW 80, lightweight anti-tank weapon, shown below, was designed to be easily carried into battle by one person , be simple and quick to operate, and to be discarded after the missile has been fired. Weighing only 9 kg in total, the weapon is light and compact enough to be carried over the shoulder. The basic design of the weapon was two sliding concentric tubes. For storage and transportation the tubes are compressed together to a length of 0.9 m, whilst for firing the launcher can be quickly extended to its full length of 1.5 m.
The main criteria for material selection were weight and cost. The tubes were constructed from Kevlar® fibre reinforced epoxy resin, using a filament winding process, and coated with polyurethane which was co-cured with the matrix resin. At an early stage of the design it was decided that a variety of fittings, such as tube end rings, sight, tracer housing, housing ring, harness clips, shoulder rest, trigger mechanism and handle would be bonded to the tubes, because drilled holes for mechanical fastenings would be detrimental to the strength of the tube. The majority of the fittings were manufactured from appropriate grades of nylon. For example the end rings were constructed of impact modified nylon - 6,6, whilst the sight and its cover were made from nylon - 11.
A number of launchers were made available to the project by the manufacturers, Hunting Engineering. These samples had been held in factory storage conditions at the manufacturers plant for 9 years prior to the investigation.
Durability studies of the adhesive bonds were also undertaken to ensure that the joints could withstand storage in a wide range of operating conditions.
Nylon to Kevlar® fibre reinforced epoxy resin laminate
Two-part acrylic
Surface abrasion
As a part of the development stage, extensive laboratory tests were conducted to select appropriate adhesives and surface pre-treatments. A two-part acrylic adhesive was chosen because it was tough the pressure pulse generated by the launch. The adhesive also had a rapid cure time, and could be dispensed robotically, minimising manufacturing costs.
Room temperature cure
The bonding was carried out at the manufacturing location.
The results of tests carried out on the bonded joints showed no apparent deterioration in the performance of the adhesive bond. Indeed, in most cases the joints had bond strengths well in excess of typical values measured at the time of manufacture. However, it should be noted that the LAW 80 samples under study had not undergone any rigorous environmental exposure or excessive stress levels.
Adequate surface treatment of both the composite tube and the nylon fittings was shown to be important for good adhesion. The lowest joint strength values were recorded when there was apparently insufficient abrasion of the composite surface, giving rise to failure at the composite-adhesive interface. Silicon containing contamination was identified on some of the nylon surfaces of non-critical components. The apparent adhesion in these areas was low.
Some inadequacies in joint manufacture were identified. These were mainly concerned with incomplete coverage of the bonding area with adhesive. In a few cases this gave rise to a slightly lower than expected joint strength.
The highest measured adhesive joint strengths were associated with a locus of failure within the composite, indicating optimum joint performance. Joints with lower bond strength had a locus of failure which was at or near to the interface.
The LAW 80 is an example of a well-proven manufactured product where adhesive bonding has been shown to meet the design, manufacturing and performance requirements for joining. The
MTS Project 3 Report No 9 Forensic Studies of Adhesive Joints. Part 1 - General Introduction and Conclusions Part 5 - LAW80 Rocket Launcher February 1996
NPL/ ESR Technology
