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. 2018 Feb 20;11(2):308.
doi: 10.3390/ma11020308.

Layup Configuration Effect on Notch Residual Strength in Composite Laminates

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Free PMC article

Layup Configuration Effect on Notch Residual Strength in Composite Laminates

Venkateswaran Santhanakrishnan Balakrishnan et al. Materials (Basel). .
Free PMC article

Abstract

The current trend shows an increasing demand for composites due to their high stiffness to weight ratio and the recent progress in manufacturing and cost reduction of composites. To combine high strength and stiffness in a cost-effective way, composites are often joined with steel or aluminum. However, joining of thermoset composite materials is challenging because circular holes are often used to join them with their metal counterparts. These design based circular holes induce high stress concentration around the hole. The purpose of this paper is to focus on layup configuration and its impact on notch stress distribution. To ensure high quality and uniformity, the holes were machined by a 5 kW continuous wave (cw) CO2 laser. The stress distribution was evaluated and compared by using finite element analysis and Lekhnitskii's equations. For further understanding, the notch strength of the laminates was compared and strain distributions were analyzed using the digital image correlation technique.

Keywords: Lekhnitskii’s equation; composite; digital image correlation; notch stress.

Conflict of interest statement

The authors declare no conflict of interest

Figures

Figure 1
Figure 1
Fiber reinforced polymer (FRP) laminates with design-based holes for joining with steel in the new BMW 7 series (source: BMW, Munich, Germany).
Figure 2
Figure 2
Glass non-crimp fabric 220 g/m² (biaxial, silane) fabric.
Figure 3
Figure 3
Specimen geometry (dimension in mm): (a) tensile specimen and (b) shear specimen.
Figure 4
Figure 4
Set-up of 3D robot assisted TRUMPF TruLaser Cell 7040 5 kW cw-CO2 laser system.
Figure 5
Figure 5
Applied stress within the crack regions of unnotched as well as notched samples.
Figure 6
Figure 6
Force-displacement curve of unnotched samples.
Figure 7
Figure 7
Strength of the laminates (σN/σO) vs. size of the circular hole (2R) in the center of the laminates.
Figure 8
Figure 8
Maximum principal stress distribution for 4 mm notched f[0°]4 laminate.
Figure 9
Figure 9
(a) Normal stress distribution vs. distance from the center of the hole in 4 mm notched f[0°]4 laminate; (b) Normal stress distribution vs. distance from the center of the hole in 4 mm notched f[45,0°]S laminate; (c) Normal stress distribution vs. distance from the center of the hole in 4 mm notched f[0,45°]S laminate; (d) Normal stress distribution vs. distance from the center of the hole in 4 mm notched f[0°]3 laminate.
Figure 9
Figure 9
(a) Normal stress distribution vs. distance from the center of the hole in 4 mm notched f[0°]4 laminate; (b) Normal stress distribution vs. distance from the center of the hole in 4 mm notched f[45,0°]S laminate; (c) Normal stress distribution vs. distance from the center of the hole in 4 mm notched f[0,45°]S laminate; (d) Normal stress distribution vs. distance from the center of the hole in 4 mm notched f[0°]3 laminate.
Figure 10
Figure 10
Longitudinal strain (ε22) field on the 4 mm notched laminate due to tensile loading. (a) f[0°]4 laminate; (b) f[0°]3 laminate; (c) f[45,0°]S laminate; and (d) f[0,45°]S laminate.

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