Biaxial flexural failure of woven composite plates

Investigated by the ring on ring bending test

Significance 

Biaxial flexural stress states are frequently encountered in thin composite structures used in a wide variety of engineering applications. For reliable operation and efficient design of these thin engineering structures, it is essential to characterize and understand their failure behavior under biaxial flexure, among other stress states. Despite a large body of research into the biaxial strength of fiber reinforced composites, studies involving biaxial flexural failure of plates are comparatively less common. Existing literature shows that several testing standards may be found for isotropic brittle materials; however, no standard test for anisotropic composite materials has been reported. One of the most commonly used methods for biaxial flexure testing of isotropic materials involves supporting a disc or plate shaped specimen on a circular ring and applying an out of plane loading at or near the center. The out of plane loading is applied either through a ball (ball on ring, BOR), or by applying uniform pressure (pressure on ring, POR) or via a smaller circular ring (ring on ring, ROR). The ROR test, being the axisymmetric analog of the four-point bending test, is particularly popular and is in fact an ASTM standard (C1499) for ceramics and has also been applied to glass, dental ceramics and also concrete.

Plate bending tests are not usually common for anisotropic fiber reinforced polymer matrix composites. To advance further the knowledge in this field, researchers from the Stony Brook University: Daniel Deland, Zongyan Zhang and led by Professor Kedar Kirane performed an in-depth analysis of the biaxial flexural failure of woven fabric composite plates. Their work is currently published in the research journal, Thin–Walled Structures.

They selected the ROR bending test for this purpose. This simple test protocol induces biaxial flexure by applying an out of plane uniaxial load via a small loading ring, to a plate or disc shaped specimen, simply supported on a larger ring. The researchers focused on applying this test method to analyze the biaxial flexural failure of woven fabric composite plates.

The authors reported that their work revealed interesting similarities and differences when compared to ceramics. To be specific, it was seen that while for ceramics the bottom surface fractures under biaxial tension, for woven composites the top surface fractures under biaxial compression. The failure pattern, however, was reported to be similar to ceramics, and consisted of several radial kink bands which initiated near the center and propagated outwards towards the specimen edges. Further, subsequent numerical stress analysis of the test revealed that the stress state in the region of the plate encompassed by the loading ring was almost exactly equibiaxial. This implied near axisymmetry of the stress state despite material orthotropy, which enabled a simple determination of the biaxial flexural strength using the in-situ measured principal strains. It also allowed approximate determination of the equibiaxial compressive strength for the woven composite, directly measuring which is usually a challenging task.

In summary, the study demonstrated the successful application of the ring on ring bending test to analyze the biaxial flexural failure of woven composite plates, which are orthotropic. Further conditions for the suitability of this test method were explored via further numerical modeling. In a statement to Advances in Engineering, Professor Kedar Kirane said their work is the first successful application of the ROR test to orthotropic materials, such as woven composites. The results show significant potential of the method for easy measurement of the equibiaxial flexural, and equibiaxial compressive strengths of woven composites.

Biaxial flexural failure of woven composite plates investigated by the ring on ring bending test - Advances in Engineering

About the author

Prof. Kedar Kirane is an assistant professor of mechanical engineering at Stony Brook University (SUNY) in New York, USA. His research focuses on understanding the fracturing and scaling behavior of various conventional and advanced composite materials. These include fiber reinforced composites, nanocomposites, geological materials, concrete, and polycrystalline alloys. Prof. Kirane obtained his Ph.D. in 2014 from Northwestern University and joined the Mechanical Engineering faculty at Stony Brook University in Sept 2017. He also holds an M.S. degree from the Ohio State University (2007) and a B.S from the University of Pune, India (2004), both in mechanical engineering. Prior to joining Stony Brook, Prof. Kirane worked as a senior researcher at the ExxonMobil Upstream Research Company and has also held a development engineer position at Goodyear Tire & Rubber company in the Engineering Mechanics group.

He is a member of ASME and EMI (ASCE). He serves on the Computational Mechanics and Modeling Inelastic Behavior of Materials committees of EMI (ASCE). He also serves as a reviewer for many prestigious international journals. He is the recipient of the Orr Early Career Award in 2020, the US Army Research Office’s Young Investigator award in 2019 and ASME AMD’s Haythornthwaite Research Initiation Grant in 2018 for proposing promising work in the field of fracture of advanced composite materials.

Prof Kirane’s research group website can be found here: https://you.stonybrook.edu/matmechlab/

References

D. Deland, Z. Zhang, K. Kirane. Biaxial flexural failure of woven composite plates investigated by the ring on ring bending test. Thin–Walled Structures, volume 148 (2020) 106585.

Go To Thin–Walled Structures

C. ASTM, 1499-05. Standard Test Method for Monotonic Equibiaxial Flexural Strength of Advanced Ceramics at Ambient Temperature, ASTM International, West Conshohocken, Pennsylvania, 2005.

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