Project TitleTesting Grips for the Proper Assessment of Mechanical Behavior in Fiber Composite Materials
Track Code2016-136
Short Description

A new grip design and method to correctly assess the mechanical properties of fiber composites. #manufacturing #tools #materials #composite #instrumentation #analytical 


Fiber composite materials – including carbon fibers – lie at the heart of a technological revolution as they provide man-made, highly lightweight materials with great mechanical properties, generating interest and applications in the aerospace and automotive industries, among others. As the need for increased strength and durability in these materials increases, so are the needs for tools that better assess their mechanical properties to ultimately inform more efficient and safer designs of fiber composite materials. Currently, stiffness – i.e., the fracture energy – is measured by pulling the materials apart using standard grips that are not able to capture the post-peak behavior and softening in these materials. A tool to better characterize and therefore develop stronger fiber composite materials with a deep understanding of their mechanical properties is needed.

Northwestern University researchers have developed fixtures – or grips – and a framework enabling to properly measure the stiffness of fiber composite materials. Currently, the stiffness is measured with standard grips that lead to misinterpretation of the failure mechanisms in these advanced materials. The rational, data-driven design of new grips developed by Northwestern researchers solves this problem. Their grips, whose design is the result of rigorous analysis of the sample-grips-machine system dynamics, allow a clear demonstration of the existence of stable post-peak softening damage, which is a crucial characteristic of quasi-brittle (or cohesive) fracture mechanics. The new information that can be obtained with the new grips is essential for realistic fracture analysis of structures made of fiber composites, and is particularly important for large structures. 

Fiber composite materials (left) being pulled apart to assess their fracture mechanism using the newly developed grips (right)    

Tagsinstrumentation: analytical, MANUFACTURING: tools, MATERIALS: composite
Posted DateJun 23, 2017 12:43 PM


Gianluca Cusatis*

Zdeněk P. Bažant    


  • Structural elements in cars, aircrafts, ship hulls, large roofs, retrofits of large seismically damaged concrete structures
  • Large windmill blades


  • Direct and accurate measurement of fracture energy
  • Accurate calibration and validation of methods and models used in quality controls and safety assessments
  • Design guided by the energy required for selected application(s), not the other way around
  • Customized grips that adapt to both the application and the loading machine apparatus available to user

IP status

A provisional US patent application (62/449,167) has been filed.­­


Marketing Contact

Arjan Quist, PhD
Invention Manager

(p) 847.467.0305



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