Master Assignment
Fiber reinforced composite materials have superior strength to weight ratio compared to metals and hence are attractive for aerospace and automotive applications. The manufacturing of engineering thermoplastic composites involves multiple steps starting from cutting of prepregs until the thermo-mechanical processing of the raw material to form the required component. At every step, cutting waste is generated and is conventionally scrapped as land-fill. However, the prepreg cutting waste possesses mechanical properties of the virgin material and is too expensive to be scrapped. Therefore, a suitable downcycling method was developed to convert the valuable prepreg scrap to downcycled parts, to be used in non-load bearing secondary structures in aerospace applications [1]. The downcycling process involves chopping of the prepreg scrap into smaller flakes (~12 mm squares) followed by compression molding of the randomly distributed bulk material as shown in the top row of Figure 1. The mechanical properties of such discontinuously reinforced materials are quite interesting and are required to be able to use this material in any application. The overall mechanical properties of such materials are lower than the continuously reinforced materials due to the randomness.
However, unlike traditional continuously reinforced composites which are highly sensitive to the presence of defects, discontinuous composites are quite insensitive to defects due to the presence of random discontinuities in the material which act as stress concentrators. This effect can be seen in the failure of the open-hole uniaxial tensile test specimen in Figure 1. Thus, it requires smaller safety factors in the design of a part.
Description
This assignment focusses on the modelling of the failure of the discontinuous composite materials made with chopped woven flakes. The objective is to develop a model which takes in to account the random orientation of the flakes and arrive at the stress distribution in a representative region of the material, leading to failure. As a first step, flat panels are to be analysed and validated with experimental data.
Approach
A preliminary approach in achieving the objective is as follows:
- Perform a literature survey to get familiar with the topic and propose a suitable modelling technique.
- Analyse experimental data (existing) to establish the phenomenology of failure. Perform additional experiments (if necessary) to collect required additional information about the material required for modelling.
- Develop a model to obtain the stress distribution in a randomly oriented flake reinforced flat laminate and use a suitable failure criteria to determine failure.
- Validate with the experimental data and document the model and the results in a thesis.
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