CFRP Thin-Ply Fibre Metal Laminates: Influences of Ply Thickness and Metal Layers on Open Hole Tension and Compression Properties

Abstract

Thin-ply laminates exhibit a higher degree of freedom in design and altered failure behaviour, and therefore, an increased strength for unnotched laminates in comparison to thick-ply laminates. For notched laminates, the static strength is strongly decreased; this is caused by a lack of stress relaxation through damage, which leads to a higher stress concentration and premature, brittle failure. To overcome this behaviour and to use the advantage of thin-ply laminates in areas with high stress concentrations, we have investigated thin-ply hybrid laminates with different metal volume fractions. Open hole tensile (OHT) and open hole compression (OHC) tests were performed with quasi-isotropic carbon fibre reinforced plastic (CFRP) specimens. In the area of stress concentration, 90° layers were locally substituted by stainless steel layers of differing volume fractions, from 12.5% to 25%. The strain field on the specimen surface was evaluated in-situ using a digital image correlation (DIC) system. The embedding of stainless steel foils in thin-ply samples increases the OHT strength up to 60.44% compared to unmodified thin-ply laminates. The density specific OHT strength is increased by 33%. Thick-ply specimens achieve an OHC strength increase up to 45.7%, which corresponds to an increase in density specific strength of 32.4%.

The Suction Panel - xHLFC and Structural Solution for Energy Efficient Aviation

“…The pre-damages in OHT relax the stress-peak near the hole and as a result, the strength of laminates with thicker plies do not reduce. Similar results are also discussed by Shin [21] and Kötter [22].…”

Developments in Laminate Modification of Adhesively Bonded Composite Joints

“…The use of thin-ply laminates brings a higher degree of freedom to layup design (both in orientation and the quantity of the individual layers) [ 146 ]. Furthermore, due to the reduced layer thicknesses and the improved resin spreading process, more homogeneous fibre distribution and smaller resin-rich regions can be achieved [ 145 ].…”

“…Furthermore, due to the reduced layer thicknesses and the improved resin spreading process, more homogeneous fibre distribution and smaller resin-rich regions can be achieved [ 145 ]. The higher number of layers and the associated higher number of interfaces also causes the shear stresses to be lower [ 146 ], and thinner plies are acknowledged to have higher resistance against matrix cracking [ 147 , 148 ]. Currently, the use of thin-ply laminates is mainly driven by the search for enhanced static mechanical performance [ 141 ] as well as the ability to suppress transverse microcracking [ 146 ] and free edge delamination [ 147 , 148 , 149 , 150 ].…”

Strength Analysis of a Rib-Stiffened GLARE-Based Thin-Walled Structure

“…It has been confirmed [ 1 , 10 , 11 , 12 , 13 ] that FML composites, due to their layered structure, have the property of limiting the propagation of fatigue cracks. Compared to glass fibre-reinforced polymers (GFRPs) and carbon fibre-reinforced polymers (CFRPs), FMLs are characterised by high impact strength [ 7 , 14 , 15 ]. At the same time, FML composites are characterised by low density [ 7 ].…”