We develop experimental techniques to improve the strength of secondary bonding of carbon/epoxy composites. The techniques include the use of laser for surface treatment, and insertion of additively-manufactured thermoplastic films in adhesive bond line in attempt to trigger mechanical interlocking. The role of extrinsic toughening, i.e. ligaments, is revealed. We also develop finite element frameworks for simulating ligament formation due to surface heterogeneity or thermoplastic film.
Imaging technology and numerical techniques allow us to track the deformation fields of heterogeneous materials under mechanical loading, based on stage-by-stage images. Full-field measurements based on image correlation technology provides a greater insight into detailed, local material properties (in a certain observation area or volume, utilizing selected inverse techniques) as well as mechanism failure. We develop simple and easy-to-use optical techniques and robust identification techniques that can efficiently process 3-D full-field data.
We develop finite element frameworks of different length-scales (micro- and mesoscale) in order to study damage mechanisms of continuous fiber-reinforced thermoplastic composites. At micro-scale, the RVE size is determined by a two-point probability function and Hill-Mandell kinematics. Transverse and shear failure in glass/polypropylene at microscale are simulated. Mesoscale model under in-plane tension is developed.
The conductive polymer fibers produced by wet-spinning and solvent doping/dedoping exhibit high electrical conductivity, high current density, high tensile strength and Young’s modulus, good flexibility and stretchability, and excellent electrical and mechanical stability. We use these high-performance fibers to fabricate stretchable electrodes in electronic circuits, wearable sensors for health monitoring, fast response wearable heating elements, low-voltage driven contractile actuators and multifunctional fiber-reinforced composites.
Carbon Fiber Reinforced Plastic (CFRP) is a well-known composite material for structural applications. Carbon-based nanomaterials and metallic nanoparticles along with a new generation of conductive polymers are some of the promising fillers that can be added to CFRP to tailor their mechanical, electrical and thermal properties. We design and process nano reinforced materials and investigate their behavior by different characterization techniques including microscopy, x-ray tomography, mechanical analysis, thermal analysis, electrical conductivity measurements and coupled electromechanical analysis.
We develop experimental techniques that are useful for the study of damage development in thermoplastic and thermoset-based composite materials at macro-scale and micro-scale (tensile, shear, quasi-static indentation, low-velocity impact, mode I and mode II fracture). We develop in situ characterizations using fiber Bragg gratings to monitor the processing of glass/polypropylene. Some projects are funded by SABIC.
Composite structures are designed to withstand severe circumstances in terms of both mechanical loading and environmental conditions. In both the short and long term this eventually leads to degradation of the structure. Understanding the related mechanisms is fundamental to composite materials. We explore the durability of composite materials, and develop structural health monitoring (SHM) techniques utilizing fiber Bragg gratings embedded in the composite system.
We are developing a specific gluing technique, called the morphing method, to couple continuum and nonlocal mechanics models for predicting material failure. The morphing method couples both models in the level of constitutive parameters in terms of the conservation of strain energy. This capability makes coupling easier to be applied to a complex structure. In addition, this method is easily transferable and nonintrusive for commercial environments.