Establishing the basic mechanical properties
Understanding the static response of materials is a fundamental starting point for understanding material and component response to loading. We make use of a range of tensile test machines including a 100kN and 250kN Instron tensile test machine at the University of Warwick and the University of Leeds respectively. We gain essential information required for the material models which are one of the key ingredients for a robust finite element prediction.
For the capture of accurate material test data, either a mechanical or optical linear extensiometer is used to record the actual extension of the sample w.r.t load. This eliminates any slippage in the clamps. Also available with this equipment is an environmental chamber and optical 3D deformation analysis equipment and software which allows us to quantify material performance and carry out digital image correlation (DIC)
Simpact have designed and developed a set of clamps which are suitable for the quasi-static mechanical testing of ultra-high strength fabrics such as aramids. Structures like these cannot be tested in standard clamping arrangement because of the premature failure that can be induced at the clamps.
Materials characterisation for moderate velocity impacts
The gravity driven drop test facility at the University of Leeds was originally designed for the research stream driven by Tim Williams (Director) to assess the impact response of automotive components for CAE model validation. The original design and research work making use of the facility can be found in the publication ‘The frontal impact response of a spaceframe chassis sportscar’
Housed in the Strength of Materials Laboratory at the Department of Mechanical Engineering at a depth approximately 5m below ground level, the facility allows for a range of impact energy levels up to 7kJ. A large falling mass is guided to impact the test sample/assembly which is mounted onto the top surface of a purpose built load cell. When the weight is raised to the desired height a solenoid is used to provide a clean release.
The load cell and an accelerometer mounted on the upper surface of the falling mass provides acceleration and force-time histories. Add our high speed video and you have the perfect controlled environment required for the correlation of finite element models. We have therefore made extensive use of this facility over the past decade for the development of components and structures designed to perform in an impact environment.
In 2015 Simpact commisioned their own drop test facility so that they could carry out this type of testing in-house and offer this impact evaluation method to their clients. It is fully instrumented and features a linear system that guides the device to be tested to the impact surface. This allows one to accurately replicate a load case which may be detailed in a standard such as the transit drop procedure described in the US Department of Defence standard MIL-STD-810G. Instrumentation in use with the facility includes high speed camera, accelerometers (1000g and 6000g) and a Kistler force platform (rated at 6kN)
Materials characterisation for high velocity impacts
Testing at high rates of strain is necessary for loadcases such as ballistic events where the effect of strain rate on material property can be significant. We have a significant amount of experince with the testing of materials at high rates of strain and this includes specialist Hopkinson Bar Equipment (HPE) in the UK which is highly relevant for determining the failure of materials and in-particular the spalling pressure of engineered ceramics.
In 2013 Simpact acquired a unique and very special piece of test equipment from the University of Leeds. The The Flying Wedge (FLW) impact test facility is a dynamic tensile testing facility capable of generating strain rates from around 10^2s-1 up to in excess of 10^4s-1. It is used for material characterisation and providing the input data required for non-linear FEA codes used for the prediction of dynamic impact events (such as our RADIOSS and LS-DYNA3D software)
In 2016 we successfully applied the principle of the flying wedge to our in-house drop test facility where the wedge impactor is mounted to the gravity drop arm. The video and images on the right show the principle of operation and a recent project characterising the strain rate dependency of 3D printed specimens. During these tests, we acheived strain rates in excess of 10^3s-1
Micro surface imaging and materials characterisation
Through our partner at the University of Warwick, Simpact have access to a Large chamber Scanning Electron Microscope (SEM) with Xray Energy Dispersive Spectroscopy (EDAX). This is used to conduct microscopy up to the nano-scale level on materials. Using this in conjunction with EDAX allows us to carry out a detailed chemical and orientation analysis. Together these provide a powerful tool to analyse the structure of a range of materials including metals, ceramics, composites and plastics.
We have our own Vickers Hardness tester in our workshop which is very useful for the evaluation of material mechanical properties at discrete points. By relating the hardness results to material tensile stress at 8% elongation, we are able to understand the variation of material properties in a part and update our models accordingly. This has been invaluable for the Simpact simulation of stamped components.