UBC engineers aim to passively iron out the forming-induced wrinkles in textile composites.
UBC engineers aim to passively iron out the forming-induced wrinkles in textile composites.

While textile fabric reinforcements have shown great potential in the design of lightweight composite structures, their formability is limited by manufacturing defects such as wrinkling, which can lessen their strength by up to 50%. However, researchers at the University of British Columbia have resolved this problem in producing strong and durable textile composites, which are widely used for prototypes, as well as in many aerospace, energy, automotive and marine applications.

The team managed to improve the effectiveness of textile composites by pulling them in two directions simultaneously in the manufacturing process to avoid unwanted fibre misalignment or fibre rupture. The work was facilitated by a custom-made biaxial clamp that stretched the textile taut and removed unrequired bumps or folds at different shear angles. As described in Materials & Design [Rashidi, A. and Milani A. S., Mater. Des. (2018) DOI: 10.1016/j.matdes.2018.02.075], after stretching the material, they could assess the necessary forces and their impact on the wrinkling and de-wrinkling of the material using image processing and 3D scanning to characterize the dimensions of wrinkles.

"Our...analysis of wrinkling and de-wrinkling of woven fabrics uncovered new insights on how various parameters such as yarn geometry or uncontrolled sources of variability during manufacturing can affect the wrinkling behavior"Abbas Milani

As team leader Abbas Milani told Materials Today, this provided “new insights on how various parameters such as yarn geometry or uncontrolled sources of variability during manufacturing can affect the wrinkling behavior of woven fabrics”. Such analysis will benefit manufacturers using the composites to better understand their mechanical behavior. Further innovation, such as including more polymer resin and fibre reinforcement options, also depends on the most up-to-date analysis in various application areas.

Predicting the minimum amount of forces required to diminish the wrinkles in useful regions of the ?nal composite parts was crucial. This can be achieved through applying appropriate boundary conditions enforced at the blank holders. Due to the trend of de-wrinkling forces shown here, a correlation could be established between 2D characterization tests and the actual 3D forming of woven fabrics, which can then be implemented in numerical simulations to devise precise de-wrinkling strategies based upon the blank holder pressure, modi?cation of the mould, or blank holder geometry.

Implementation of the proposed approach via numerical simulations is now being worked on, with a hybrid modeling framework also being developed to predict the forming pattern of woven fabrics over 3D surfaces. In addition, the team are looking at an inverse design optimization process where the forming simulation can initially estimate the regions prone to wrinkles, along with corresponding shear angle ranges. The next stage of the research involves conducting tension-assisted forming trials with a modified blank holder geometry concept, to impose the optimum amount of boundary forces during forming and mitigate the wrinkles ‘passively’.