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How can toughness be improved in a composite material?

asked 2016-05-29 19:00:30 -0500

How can toughness be improved in a composite material?

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answered 2016-05-29 19:07:36 -0500

Johann Heun gravatar image

The energy absorbing capability of composite materials is a consequence of the “work of fracture” arising from the mechanisms occurring during catastrophic fracture. The inherent brittleness of composites ensures that they do not undergo the yield processes characteristic of ductile metals but on the application of load, deform elastically up to the point of fracture. A number of modes of deformation are available to complex multiphase composite materials. The primary energy absorbing mechanisms in fibre-reinforced plastics are:

• cracking and fracture of the fibers, • matrix fracture, • de-bonding (pull-out) of fibres from the matrix, • delamination of the layers making up the structure.

The primary mechanical properties of composites (tensile strength and stiffness) are dominated by the fibre reinforcement. The matrix phase on the other hand contributes significantly to the secondary attributes such as resistance to out of plane loading and damage tolerance. Of the four modes of deformation/energy absorption available to composite materials, fibre fracture is by far the most significant. The increased work of fracture obtained from higher and higher strength fibres is shown to increase the specific energy absorption. This can only be achieved however if the tendency of the composite to delaminate under load is reduced. The toughness of the resin thus plays a significant role in optimising its ability to absorb energy. This is particularly useful when designing “dual function” components that have a structural purpose in addition to acting as an impact safety device.

It must be assumed that all engineering components in service contain defects to some degree or another. One may minimise the extent, size and effect of induced flaws by careful design manufacture and condition monitoring, but there will always be a risk. In the case of composite materials used in a harsh environment such as Formula 1, delamination represents the most likely mode of failure. The interlaminar shear strength of a composite is a good measure of its ability to resist out of plane loading. It cannot account however for the presence of defects induced during service or manufacture. The material thus requires the ability to resist the propagation of such flaws under load. Improvement of interlaminar fracture toughness is thus paramount in order to improve reliability and reduce the requirement for over conservative design. Higher fracture toughness will furthermore open up more and more design opportunities otherwise precluded to composite materials.

Ref: Enhancing the exploitation and efficiency of fibre reinforced composite structures by improvement of interlaminar fracture toughness, Gary Savage.

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In order to improve interlaminar fracture toughness a toughened resin should used- many brands are available.

Rob Mueller gravatar imageRob Mueller ( 2016-05-29 19:10:21 -0500 )edit

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Asked: 2016-05-29 19:00:30 -0500

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Last updated: May 29 '16