Abstract
This paper studies the effect of seawater immersion on the fatigue behavior of notched carbon/epoxy laminates. Rectangular cross-section specimens with a central hole were immersed in natural and artificial seawater for different immersion times (0, 30 and 60 days), being the water absorption rate evaluated over time. After that, fatigue tests were performed under uniaxial cyclic loading using a stress ratio equal to 0.1. After the tests, the optical microscopy technique allowed the examination of the failure micro-mechanisms at the fracture surfaces. The results showed that saturation appeared before 30 days of immersion and that water absorption rates were similar for natural and artificial seawater. The S–N curves showed that the seawater immersion affects the fatigue strength, but there were no relevant effects associated with the type of seawater. Moreover, it was also clear that fatigue life was similar for long lives, close to 1 million cycles, regardless of the immersion time or the type of seawater. On the contrary, for short lives, near 10 thousand cycles, the stress amplitude of dry laminates was 1.2 higher than those immersed in seawater. The failure mechanisms were similar for all conditions, evidencing the fracture of axially aligned fibres and longitudinal delamination between layers.
Highlights
Composite materials are used in various engineering applications, such as marine, aerospace, civil, offshore, sports, and automobile industries, due to their high specific strength and stiffness, as well as their high fatigue and corrosion resistance
When delamination appears on the laminate, there is a reduction in the strength, stiffness, and fatigue life of the laminate, which can lead to catastrophic failure of the entire structure
In terms of fatigue test results, the S–N diaFatigue tests at constant load amplitude were performed in tension (R = 0.1), for gram was the main tool used to analyse them. This was based on the stress-life approach which the mean load was inputted by software, and the maximum and minimum axial and represented the fatigue life dependence on stress
Summary
Composite materials are used in various engineering applications, such as marine, aerospace, civil, offshore, sports, and automobile industries, due to their high specific strength and stiffness, as well as their high fatigue and corrosion resistance. Ocean energy devices made of composite materials operate in a very severe environment, and the selected materials must be thoroughly qualified to reduce the risk of failure in service [4]. Water uptake in this family of materials as well as its effect on their mechanical behaviour, treated as an uncoupled phenomenon, has been widely studied [5,6,7,8,9,10,11,12]. There are some studies on the use of composites in adverse conditions, the durability of CFRP composites exposed to moisture or wet conditions needs further research to make them applicable to external applications with limited monitoring or inspection [18]
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