Identifying the sensitivities of transverse cracking in composites

Fiber-reinforced composites are widely used in aerospace and other high-tech industries. Understanding how their microstructure and the strength of the fiber-matrix interfaces affect their failure properties can lead to manufacturing stronger materials. A recent study at the University of Illinois at Urbana-Champaign developed a model to identify the sensitivities of transverse cracking, one of the key failure processes present in composite laminates, on details of the composite microstructure.

Composite laminates used in aerospace application are typically made of layers of carbon fibers with varying orientations embedded in epoxy. For example, the composite laminate can be composed of a carbon/epoxy layer with the fibers oriented in the 90-degree direction sandwiched between two 0-degree plies. The fibers are each about seven microns in diameter, or about one-seventh of the thickness of a human hair.

Transverse cracking of composite laminate
Left: Optical image of a composite laminate used in the transverse failure experiments. Right: Representative image of a transverse crack spanning the 90 ply. As apparent from this optical image, the transverse cracks extend primarily along fiber/matrix interfaces. Credit: University of Illinois

We know from experiments that cracks propagate transversely across the 90-degree plane, then stop when they reach the interfaces with the 0-degree plies. So we developed a method that allows us to simulate hundreds of fibers in a realistic system and study how the failure response is affected if we change the location of a single fiber or of many fibers, or the strength of the interface,” said Philippe Geubelle, a professor in the Department of Aerospace Engineering.

In this new method, optical micrographs are taken of the 90-degree ply and the location of all of the fibers are extracted to construct a realistic computational model of the ply. Similar studies have been limited to tens of fibers.

With the special finite element method we have developed to simulate the transverse cracking of the 90-degree ply, we can simulate hundreds of fibers,” Geubelle said. “The most we’ve done so far is close to 3,000 fibers. Because the crack propagates primarily along the fiber-matrix interfaces, our model emphasizes the cohesive failure of these interfaces,” he said. “In addition, we have developed the ability to extract efficiently the sensitivity of the failure event with respect to the properties of the microstructure. These properties include the location and size of the fibers, and the failure properties of the fiber-matrix interfaces. We can also compute the sensitivity of the failure event with respect to the parameters (average, standard deviation, etc.) that define the distribution of these microstructural parameters.”

The model is validated against experimental observations performed in Prof. Nancy Sottos’s group in the Department of Materials Science and Engineering at the University of Illinois.

Of course, you could get these sensitivities experimentally, with every conceivable variation, to see what the effect is on the failure event,” Geubelle said. “To do this numerically is much more efficient.”

The work is supported by a grant from the Center of Excellence on Integrated Multiscale Modeling with funds from the Air Force Research Laboratory and the Air Force Office of Scientific Research, in collaboration with researchers from Johns Hopkins University and the University of California, Santa Barbara.

 

Source: University of Illinois – Aerospace Engineering


Leggi anche

The focus of this work is the aircraft fuel system and the objective is to develop a thermoplastic composite material which is suitable for use in aircraft fuel systems. Read the project, it won our first call for papers….

Leggi tutto…

Together with GKN Aerospace Deutschland GmbH, TUM – Chair of Carbon Composites, SGL Carbon, Augsburg University of Applied Sciences, and under the co-founding authority of Bavarian Ministry of Economic Affairs, Regional Development and Energy, Cevotec started a pioneering R&D project: the full automation of sandwich structure production. …

Leggi tutto…

Thanks to high-performance aerospace-grade materials, the importance of additive manufacturing (3D printing) continues to be recognized within the aerospace industry. Here, Scott Sevcik, VP Aerospace Business Segment at Stratasys, one of the leading manufacturers of additive manufacturing solutions, looks at some of the current trends and developments that highlight the technology’s ongoing ability to deliver opportunities for aerospace manufacturers and their suppliers…

Leggi tutto…

Nano-Tech announced the partnership with Mecaer Aviation Group for the realization of the interior of the latest generation helicopters. The Italian company will provide special “flame retardant” materials for helicopter cabins. Components have passed the rigid safety tests of Far.

Leggi tutto…

The use of thermoplastic composites (TPCs) in the transport industry has increased in recent years due to the advantages offered by these materials in terms of recycling, reprocessing and repairing. TPCs can lead to a reduction in the amount of waste materials and virgin raw material required, thus lowering the environmental impact. This article – published in the March issue of Compositi Magazine – talks about SPARTA Project that aims to develop an innovative recycling method for TPCs….

Leggi tutto…