SAMULET Project 5 Task 5.1.3 Superplastic Forming and Task 5.5.2 Development of Inspection Methods for Novel Materials

This EPSRC project was split into two independent parts. The first part was about investigation of different aspects of exploitation of superplastic forming tools in order to increase their rather limited life and therefore reduce substantial tooling costs. The second part of the project was concerned with the development of new transduction systems for inspection of composite structures.

Superplastic forming (SPF) of titanium alloy sheet is characterised by high process temperatures, in which tools operate at typically 900 C for several hours to form components. Unfortunately the service life of these tools is not predictable and it is not uncommon for tool failure to occur early on in service life. This has a significant impact on the total cost of the process. The first part of this EPSRC project investigates properties of SPF tool materials and models tool behaviour during SPF cycles in order to better understand tool performance and formulate risk mitigation strategies. The EPSRC project was linked with a TSB project covering additional aspects of SPF tooling such as non-destructive tool testing and adhesion of tool and the formed titanium sheet.
The second part of this EPSRC project was concerned with the development of a large area coverage ultrasonic inspection system for imaging of composite materials. The project developed a new design methodology for sparse 2D ultrasonic array configurations, which utilised efficient GP-GPU processing techniques. Importantly, the array design includes the inspection material and coupling layers and the output enables the design engineer to extract array parameters (sensitivity, resolution and contrast) to aid the design process. The final output is a coverage map of the inspection material. This approach was used to design, fabricate and evaluate a large area, sparse 2D array.

This EPSRC project was split into two independent parts. The first part was about investigation of different aspects of exploitation of superplastic forming (SPF) tools in order to increase their rather limited life and therefore reduce substantial tooling costs. It was interlaced with an industrially funded project which in turn used TSB funding. The EPSRC funded part was mainly about proposing procedures and ranges of testing parameters to establish mechanical and thermal properties of various heat resistant tool materials suitable for SPF. It was also about structural characterisation of cast blocks used for machining SPF tools, which gave a valuable insight into the casting process of these blocks. Another main task was the creation of a finite element (FE) model of SPF tool behaviour during simulated thermal cycles representing industrial conditions. The model used material properties established in the first part of the project (financed by TSB). The model was initially used to simulate behaviour of a simple shape block in order to find a relationship between various material properties and stress amplitude as well as accumulated plastic strain in this block. It was eventually used to simulate thermal and mechanical stress cycles in the industrial tools (financed by TSB), which proved its suitability. The modelling part culminated with formulating FE modelling guidelines for the industrial partner. Other aspects covered by TSB funding were non-destructive testing of tools and adhesion of tools and the material formed. Altogether the progress achieved in tool characterisation, numerical modelling of tool behaviour and material/tool interaction has been an important step forward towards understanding the tooling problems in SPF and finding solutions to these problems.
The second part of this EPSRC project centred on the development of an ultrasonic array imaging system for use with composite materials. A fast, efficient simulation framework was developed using GP-GPU hardware to enable full 2D array configurations to be evaluated. This approach implemented the Total Focussing Method (TFM) imaging algorithm and simulated the ultrasonic system response for every point in the structure. This created a volumetric map for the array design parameters of sensitivity, resolution and sidelobe level (contrast). Moreover, further analysis produced a coverage map to indicate the suitability of a particular array configuration for the intended inspection scenario. This approach was used to design a 50mm diameter, sparse 2D ultrasonic array. Initial experimental evaluation demonstrated the potential of this transduction approach for use with composite structures.

Follow on funding through Strathclyde's IAA and RCNDE Technology Transfer funds were secured to advance the 2D ultrasonic imaging system and install the equipment at Rolls Royce Aerospace.