The Performance of Adhesive Joints (PAJ) - A UK Initiative

Background

To operate effectively, UK manufacturing industry requires consistent test methods to assess engineering materials and their processing routes. The Department of Trade and Industry (DTI) supports this need through the Measurement Technology and Standards (MTS) budget. Adhesive bonding is a key enabling technology for improving the competitiveness of industry. The Centre for Adhesive Technology (CAT), based at TWI, was therefore commissioned by the DTI to establish specific areas where validated test methods would increase confidence in predicting the performance of adhesive joints. The CAT consulted about 100 organisations, by both telephone and direct interview over the period November 1991-January 1992. Opinions from industrial sectors were obtained, including aerospace, automotive, marine, building and construction, machine tools, light engineering, electrical, electronics, precision instruments, packaging and footwear. These views were evaluated, leading to recommendations on priority 'areas for measurement work.

Introduction

The survey identified measurement methods for use in design, environmental durability and process control as priority areas and five projects were defined. Tendering took place in July 1992 and contracts were placed for work to start in December 1992 to a total value of £5.4m over three years, funded 100% by the DTI.

The projects were monitored by the CAT, with technical co-ordination provided as part of the control system. The projects concluded in April 1996, with a wealth of issues being addressed.

The five projects and their teams were as follows, with Project Managers identified by italics:

• Project 1. Basic mechanical properties for design: National Physical Laboratory (NPL), TWI and Bristol University.
• Project 2. Failure Modes and Criteria: AEA Technology, Imperial College and Surrey University.
• Project 3. Environmental Durability: AEA Technology, Oxford Brookes and Loughborough Universities, Imperial College and Defence Research Agency.
• Project 4. Measurements and Characteristics to Define Surface Condition: AEA Technology, Oxford Brookes, Loughborough and Surrey Universities.
• Project 5. Measurements of Optimising Adhesive Processing: NPL,IBM (UK) Ltd, SATRA, Taywood Engineering and PIRA International.

A brief review of the main results is presented.

Conclusions for the complete project suite

• Validated test methods have allowed mechanical properties to be measured and so increased the confidence of engineers specifying adhesives.
• Stress analysis, using FE analysis in conjunction with failure criteria, can give a good indication of the fitness for purpose of a joint.
• Design of a smart joint requires astute judgements and asking advice pays dividends.
• Surface pre-treatments must be appropriate to the performance specification.
• The manufacturing process can be optimised through statistical analysis.