Stress analysis in carbon/epoxy composites using Lcr waves

Abstract

This work presents the application of an ultrasonic method to measure stresses in unidirectional carbon fiber composites with epoxy matrix (HexTow Õ AS4/Hexply Õ 8552). This kind of composite is largely employed as a structural material in the aeronautical industry. The ultrasonic method is based on the acoustoelastic principle, a principle that holds that wave speed is affected by variations in strain in the material. We employ critically refracted longitudinal waves (Lcr waves) and relate their time-of-flight with applied strains and stresses. We first performed tests on a polygonal specimen evaluating the influencing factors on the results, that is, temperature and transducer positions, as well as their effects on each fiber direction: 0 , 45 , and 90 . Tensile tests were next performed on rectangular specimens, as we sought, for each fiber direction, the relation between stress and wave speed variation, otherwise known as the acoustoelastic coefficient. The results showed that the wave speed was sensitive to the stress variation along the fiber direction (0 ) and nearly insensitive to any other direction. Also, temperature (between 20 C and 27 C) was not a relevant factor for waves propagating along the fiber. These findings support the notion that the method holds promise as an alternative to measuring stresses in multidirectional composite materials.

Comparison of the L cr wave TOF and shear‐wave spectrum methods for the uniaxial absolute stress evaluation of steel members

“…Egle and Bray studied the sensitivity of ultrasonic waves and found that the Lcr wave velocity was most affected by stress but least affected by material texture, and they evaluated the mechanical bending stress in steel plates by changing the frequencies of ultrasonic probes . Dos Santos et al presented an application of the Lcr wave method to stress measurement in unidirectional carbon fibre composites and found that the Lcr wave speed was sensitive to the stress along the fibre direction but insensitive to any other direction. Javadi et al used the Lcr wave to measure the welding residual stress distribution and evaluated the through‐thickness distribution of stresses.…”

An Ultrasonic Longitudinal Through-Transmission Method to Measure the Compressive Internal Stress in Epoxy Composite Specimens of Gas-Insulated Metal-Enclosed Switchgear

“…However, as this research is based on a composite material with uniaxial stress, Equation (1) can be applied in composites-only for uniaxial stress. Auteliano has applied equations for isotropic materials by using ultrasonic critically refracted longitudinal waves to investigate the uniaxial stress in carbon fiber composites with epoxy matrix [10].…”

“…These include the hole-drilling method, ring core method, slot-cutting method, indentation method, layer removal method, etc. The non-destructive methods are based on the relationship between the internal stress and physical parameters, and include five main methods: X-ray diffraction method and neutron diffraction method, based on the evaluation of interplanar spacing in crystal materials [9]; the magnetic method, based on the magnetostriction effect in ferromagnetic materials [10]; the photoelasticity method, based on the birefringence exhibited by certain transparent materials [10]; the ultrasonic method, based on the relationship between stress and ultrasonic wave velocity [9].…”

“…There is only a report investigating the acoustoelastic effect in the fiber-reinforced epoxy composite with epoxy matrix, by Santos et al [10], who employed the critically refracted longitudinal waves. They showed that the propagation time varied linearly with the tensile internal stress in the fiber direction of 0 • , 45 • , and 90 • and the propagation time was the longest in the 0 • direction.…”

A comparison of the use of critically refracted longitudinal waves and magnetic Barkhausen noise for stress measurement in API 5L X70 steel

“…2 L cr waves have been used to measure residual stress generated during welding, [3][4][5][6] residual stress in railroad wheels, 7 and applied stress in composite materials. 8 Measurement of magnetic Barkhausen noise (MBN) is another NDT technique that can be used to evaluate stresses in ferromagnetic metals, such as steels. This new technique has been studied for the last two decades, and suitable applications, equipment, and measuring procedures are currently being investigated by researchers.…”