Papers by Author: Robert A.W. Mines

Abstract: This paper outlines the findings of an on-going research study investigating the properties of a range of steel and titanium-based micro-lattice structures manufactured using the selective laser melting (SLM) technique. Initially, tension tests have been conducted on strands manufactured at different build angles. Micro-lattice block structures, with struts oriented at +/-45^o were then tested in compression at quasi-static rates of loading. The failure mechanisms have been investigated using both optical and scanning electron microscopy. These tests have highlighted the attractive properties offered by these complex architectures.

Abstract: Stainless steel micro lattice structures, manufactured by selective laser melting, have the potential to be used as core materials in twin skinned structures. The configuration considered here is body centred cubic. One of the major structural performance requirements for such twin skinned structures is foreign object impact. The paper describes the series of steps taken to simulate (using DYNA) and validate the low velocity foreign object impact behaviour of twin skinned panels with micro lattice cores. This includes the validation of a three beam model for each micro strut, the modelling of node behaviour, and the modelling and validation of compressed micro lattice blocks, and of full foreign object impact panel behaviour.

Abstract: The paper discusses the compressive behaviour of two materials, the conventional aluminium honeycomb and the new titanium alloy micro lattice blocks. The new titanium alloy micro lattice structure is being developed as core material candidate in sandwich construction for aerospace application. Experimental tests have been done on the blocks in order to compare its property with the aluminium honeycomb. Compression strength as well as compressive behaviour of both materials are compared and observed. The mechanisms that contributed to the differences in their performance are discussed and this will be used to improve the geometrical and structural design of micro lattice structure in order to achieve properties that are superior or at least comparable with that of aluminium honeycomb.

Abstract: This paper is a study of the drop weight impact behaviour of small sandwich panels of carbon epoxy skins with aluminium honeycomb and titanium alloy micro-lattice cores. A series of experimental tests have shown that the specific impactor penetration behaviours are similar for both cores. The reasons for this are a result of the detailed deformation and rupture behaviour of the two types of core. The deformation and rupture mechanisms of honeycomb and micro-lattice structures will be discussed in general terms, and these observations will be used to inform discussion of actual deformation and rupture in the panel tests. In this way, micro energy absorbing mechanisms will be related to panel performance, and conclusions on the way forward for improved penetration performance using other core materials and geometries will be identified.

Abstract: This paper discusses the penetration behavior of fully supported sandwich panels with micro-lattice and foam cores, and composite skins. This behaviour is of importance during foreign object impact and perforation of sandwich structures. Experimental results are given for quasi-static penetration of micro-lattice and foam blocks, and it is shown that these two cellular materials are comparable. Experimental results are also given for drop weight penetration of fully supported skinned panels, and it is shown that skin failure and core penetration are also similar for the two core materials. It is concluded that there is scope for improving the performance of micro-lattice structure and so making such material superior to that of aluminium foam.

Abstract: Structural foams are used as cores in sandwich construction. In the application of foreign object impact loading of sandwich structures, the core will suffer dynamic multi axial deformation and crush. This means that experimental study is required for the crush behaviour of structural foams at various strain rates, and numerical simulation foam models need to be calibrated with dynamic data. A number of foams are considered, namely Divinycell PVC foam, Rohacell PMI foam and Alporas aluminium foam. Also, new generation metallic micro lattice structures are discussed

Abstract: The paper describes mechanical property tests on a Concorde aircraft tyre rubber. The tyre rubber is taken from the tyre tread, and consists of nylon reinforcement, laid up in an angle ply form. The constitutive behaviour of the rubber is characterised using the Mooney Rivlin approach, in which deformation is expressed in terms of strain energy. Static and dynamic tensile tests are conducted along the major reinforcement and minor reinforcement axes in the plane of the tread, and compression tests are conducted through the tread thickness. This data is then input into a finite element model of the tyre, using DYNA.

Abstract: Material properties are required for the numerical simulation of the impact progressive collapse of metal foam cored polymer composite sandwich beams, using LS-DYNA. As far as the metal foam, Alporas, is concerned, multi-axial tension and compression data is required. This includes large scale crush and tensile rupture. An Arcan test fixture was developed, in which a sample of foam can be subject to tensile and shear deformation simultaneously. The data was also used to calibrate the crushable foam material model in LS-DYNA. For the skin, tensile and compression data was generated for a cross ply glass fibre thermoplastic laminate. The data was then used to calibrate the composite damage material model in LS-DYNA. Inclusion of calibrated material models into the simulation of the progressive collapse of metal foam cored composite sandwich beams will be briefly discussed.