An integrated (ICME) approach to multiscale modelling of the fabrication and joining of powder processed parts

The applicability of metallic powder based production methods such as HIP or additive layer manufacturing (ALM) are restricted by an inability to define the process parameters with sufficient accuracy to provide the quality required for industrial production. Similarly the implementation of the joining technologies needed for component fabrication is limited by a lack of understanding of both the gas-liquid phase interactions and the effect of the solid state phase transformations that occur in the relevant alloy systems. Traditional solutions, based on practical trials and physical assessment, are both costly and time consuming and for the long service lives encountered in the energy and propulsion industries are not feasible while empirically based phenomenological modelling approaches cannot provide the required fidelity.
To address these industrial needs a multiscale modelling approach is proposed which combines experimental validation with the application of materials modelling, at the short length scales required to capture the relevant physics, together with the development of techniques to incorporate the predicted behaviour in a consistent manner at higher length scales for application to component level simulations.
The multiscale model integration will consist of a number of component parts commencing with new multiphysics based computational fluid dynamics calculations of the short length scale fluid flow and liquid/gas interactions in welding and additive manufacturing. These will provide data on porosity formation which will be combined with cellular automata predictions of grain structure. Novel methods will be developed to combine this fine scale data in a finite element based crystal plasticity framework to define representative volume elements for modelling the macroscopic behaviour in component stress analysis.
The component level simulation work will build upon the EPSRC Manufacturing Fellowship of Prof Smith on a whole-life approach to high integrity welding technologies by utilising the knowledge gained on the effect of the microstructural changes imposed by welding. These have a profound influence on a weld's resistance to in-service degradation and upon its sensitivity to the presence of cracking. The microstructural characterisation data available on 316L stainess steel from the Fellowship work will also provide a basis for the model validation.
A key part of the developments in this project will be the extension, from typical single value deterministic models, to statistically based descriptions of material properties and process variability. This is a challenging activity but it is essential that modelling tools become capable of predicting the scatter that is seen in real materials. A successful solution will not only generate novel science but will clearly lead to the development of probabilistic lifing methods with risk based outputs for decision making which have clear benefits for industry. This approach provides the prospect of a better understanding of in-service performance of components and welds in both the existing UK nuclear reactor fleet and in any industrial sector where long term structural performance is important.
Similar developments in the US have led to a new field known as Integrated Computational Materials Engineering (ICME). This is a multi-disciplinary approach to product design that offers huge economic potential and the successful implementation of ICME will revolutionise the way components are being designed and manufactured. This proposal will address the modelling and design challenge using an ICME based approach on industrial demonstrators of 316L stainless steel HIPped and TIG welded parts. The demonstrators, supplied by the partners from the aerospace and energy industries, will show the benefits that can be achieved in different market sectors. The proposed programme will be the first attempt in the UK to use ICME tools on large industrial scale demonstrators.

The novel modelling technologies proposed will provide a scientific breakthrough in terms of modelling capability and the application of multiscale approaches. The impact on the multi-scale modelling academic community, of the developments of the modelling tools and the mechanistic understanding through characterisation, will be significant as it will facilitate the scientific understanding of the manufacturing processes studied The development of the statistical and stochastic modelling approaches, will offer a considerable advantage to the academic materials science community in allowing the prediction of distributions of behaviour rather than conventional deterministic solutions. In addition, the further validation of this capability will allow the design engineers within the energy and aerospace industries to have an improved tool for life prediction. It is anticipated that the software integration requirements of ICME and the ability to analyse large volumes of data will also lead to advances in mathematics and computer science. Although the targeted demonstrators are aimed at specific industrial application the approaches used will also be of generic value to other manufacturing methods and materials.
The project will positively impact on manufacturing industry in the energy and aerospace sectors through the use and implementation of the ICME tools by both original equipment manufacturers (OEMs) and their supply chain. Initial exploitation of ICME is in the aerospace sector and the UK has a 17% global market share in aerospace industry revenues making it the largest in Europe and second to the US worldwide. In 2012, the industry had a turnover of some £20 billion and consequently the financial impact of ICME is potentially highly significant. It has been shown (G. Goldbeck, The economic impact of molecular modelling of chemicals and materials. Goldbeck Consulting Report, 2012) that "There is strong evidence that the integration of materials modelling with engineering workflows (so called Integrated Computational Materials Engineering) has been carried through successfully with a large return on investment (ROI)." (where ROI is the ratio between revenue generated from products resulting from a project in which materials modelling was used and the investment in materials modelling). The returns associated with modelling implementation have been reported to range from 2 to 20 thus justifying an expectation of benefits in excess of 5:1
The adoption of ICME methods can result in significant business benefits, for example, Rolls-Royce have achieved reductions in casting scrap (in excess of US$5M p.a.) and reduced (by 90%) the number of forming trials required for hot isostatic pressing (HIP) developments thus shortening the time to market of new products. As a consequence to maintain competitive advantage, Rolls-Royce is fully committed to continually extend the use of Materials and Process Modelling within its business. For solidification processes and powder joining, successful demonstration of modelling capabilities will lead to high technology readiness research and demonstration of component scale feasibility, particularly in the Energy and Aerospace fields. The ultimate exploitation will lead to far fewer large scale tests and trials and enhanced component capabilities. This will subsequently encourage future research to push scientific understanding further still.
Additional benefits to the UK economy will be achieved through the increased adoption of ICME giving rise to reduced time to market, lower costs and improved competitiveness. The initial applications of ICME will be focussed on the energy and aerospace sectors and this will contribute to societal benefits resulting from cleaner energy generation and more efficient transport solutions.