Lightweight chassis structures

Expertise in this area has two complementary themes; adhesively bonded structures and fibre reinforced polymer (FRP) composites.

Structural weight is reduced using advanced FRP materials which are often joined using structural adhesive bonding.

Work in both areas is supported using advanced FE modelling software, a mechanical testing laboratory with seven state of the art electro mechanical and servo-hydraulic testing machines, composite and adhesive bonding manufacturing laboratories and a full range of micro-structural and surface analysis materials characterisation facilities.

Adhesively bonded structures

Design allowables

Spreadsheet based specific adhesive joint analysis have been developed. Basic stress analysis of adhesive joints can be undertaken using these or more generally using a simple linear finite element analysis. The approach taken depends on the geometrical complexity of the joint. In either case, it is necessary to use the results to determine a safe joint design. Methods for determining design allowables have been developed that can be used to size a joint to carry known static, fatigue and sustained levels of loading.

Service lifetime predictions

Adhesively bonded joints have to function in a complex environment of fluctuating loads, temperatures and moisture levels. Exposure to these service parameters all degrade the performance of the bonded joints. A progressive damage FE modelling approach has been developed that serves as a virtual joint test, providing the entire loading response of a structure up to the point of failure, Fig 2.

Progressive damage through a peel joint that had been exposed to a hostile hot-wet environment image
Figure 2: Progressive damage through a peel joint that had b [...]

FRP composite materials

Damage micro-mechanisms

Work in composites materials is based on a thorough understanding of the micro-mechanical mechanisms that are active in the failure process of the composite. Many fibre architectures have been studied from the simplest systems reinforced with unidirectional fibres through to the very latest 3D woven fabrics, Fig 3.

Based on this understanding, a range of problems of relevance to automotive design have been studied (including closed-form design rules for notched composite materials, experimental and numerical studies for bolted composite single and double lap joints,the characterisation of impact damage in composite plates).

Observation of tow fractures in a 3D woven composite using micro-CT analysis. (Courtesy of Luca Baiocchi)
Figure 3: Observation of tow fractures in a 3D woven composi [...]

Structural health monitoring

It is important to be able to detect damage in composite materials and bonded structures. Work in this area is based around the use of optical sensors (as chirped fibre Bragg gratings) which can either be embedded within a composite structure or bonded to its surface. By responding to changes in strain, over a gauge length which can vary from 10 mm to 120 mm, the onset and propagation of damage can be monitored.

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