Impact Response of Curved Composite Laminates: Effect of Radius and Thickness
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Impact Response of Curved Composite Laminates: Effect of Radius and Thickness William Harris 1
2
& Constantinos Soutis & Christopher Atkin
3
Received: 3 June 2020 / Accepted: 13 July 2020/ # The Author(s) 2020
Abstract
This paper presents the results of drop-weight impact testing (5 J to 30 J) on curved ±55° E-glass-epoxy laminates of varying radii and wall thickness. Three radii (75 mm, 100 mm, and 125 mm) on laminates with an effective wall thickness of 2.5 mm, and three wall thicknesses (2.5 mm, 4.1 mm, and 6.6 mm) with a radius of 100 mm were investigated. The damage pattern remained consistent, with the exception of the damage area, across the tested energies and was dominated by internal matrix cracking and multiple delaminations. However, no damage was recorded following a 5 J impact on the 2.5 mm thick laminates with 100 mm and 125 mm radii, all energy was absorbed elastically, while the laminate with a 75 mm radius of curvature developed a damage area of over 80 mm2. The thicker laminates showed a reduced overall damage area but a greater number of delaminations. The relationship between laminate thickness and delamination threshold load was found to be in line with impact testing of flat plates, varying with the laminate thickness to the 3/2 power. However, the simplified beam theory and a fracture mechanics model developed for the prediction of delamination threshold of flat plates was found to underestimate the delamination threshold load (DTL) of the curved laminates studied by about 40%. An increase in the laminate’s flexural modulus of a factor of two is required to bring the model’s predictions in line with the DTL values measured experimentally, highlighting how curvature can enhance bending stiffness and alter damage evolution. Finally, a significant finding is that the DTL of the curved plates is around 15% lower than the value measured for the whole cylindrical pipe of same specifications. Testing curved sections rather than a whole pipe could reduce effort, but further work is required to confirm this statement. Keywords Polymer matrix composites . Curved plates . Impact . Delamination . Bending stiffness . Critical load
* William Harris william.harris–[email protected] * Constantinos Soutis [email protected] Extended author information available on the last page of the article
Applied Composite Materials
1 Introduction The effect of impact, and the consequence of the associated damage mechanisms, is a key consideration in the use of composite material and has been widely researched [1–4]. There is a wealth of knowledge regarding the use of composite materials in the aerospace [5] and sports sectors, where the material has seen successful implementation and growth. However, it is now not uncommon to find the material in more diverse applications, including offshore oil and gas and renewable energy. As confidence in the material grows in these new arenas, it is expected that the use of composites will continue to increase [6] and soon the material will be u
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