Reasrarch On Air-coupled Ultrasonic Evaluation Method For Dynamic Viscoelasticity Of Composite Materials

Compared with traditional materials, composite materials have been widely used in various industries because of its high specific strength and stiffness. For example,advanced composite materials are widely using in the supersonic aircraft, high-speed trains, underwater nuclear submarines where suffer high temperature and pressure. With the application environment of composite materials is getting worse, the impact of vibration, noise and shock of application environments for composite structures also can not be neglected, these negative factors are the most direct reasons for the fatigue,damage, security shorten the life of composite structures. So, it is very necessary to master the internal damping mechanism of composite materials.As a important mechanical property, dynamic viscoelastic can reflect inherent damping of composite materials. In order to understand the internal damping mechanism of composite materials, it is particularly important to master and evaluate the dynamic viscoelastic of composite materials quickly and effectively. This article aims to proposed the nondestructive evaluate method of the dynamic viscoleastic and carried out the application of nondestructive evaluation for dynamic viscoleastic of composite materials.Firstly, briefly introducted the research background and research status of the field concerned with topic. The evaluation methods of the dynamic viscoelastic of the material mainly include dynamic mechanical analysis(DMA), ultrasonic immersion transmission method and contact-type ultrasonic pulse reflection method. But, these evaluation methods require contacting with the material, so during the evaluation process, it will cause pollution or damage to the material. In order to solve the above problems, based on the characteristics of non-contact and non-intrusive of air-coupled ultrasonic in this paper to achieve the evaluation of the dynamic viscoleastic of material by the air-coupled ultrasonic.Secondly, a theoretical study on the evaluation method for the material dynamic viscoelasticity by air-coupled ultrasonic was carried out. According to the basic theory of viscoelastic properties and air-coupled ultrasonic testing technology, and basing on the theory of ultrasonic immersion transmission method and contact-type ultrasonic pulse reflection method, use loss angle tangent value as the parameter of evaluation method, the methods of evaluating the material dynamic viscoelaticity by air-coupledultrasonic transmission method and air-coupled ultrasonic surface method were obtained. And this provided theoretical basis for the research of inspection and evaluation method.In order to verify the reliability of the evaluation results of dynamic viscoelasticity by the new evaluation method, the rubber material is used as the experimental material,evaluating the dynamic viscoelaticity of the rubber material by contact-type ultrasonic pulse reflection method and air-coupled ultrasonic evaluation method seperately, and then according to the experimental results, It is concluded that the method of air coupled ultrasound is reliable for evaluating the dynamic viscoelasticity of the material.Finally, The experimental study for evaluating the dynamic viscoelasticity of the composite was carried out, and the experimental platform was built, and a number of carbon fiber composite samples were made. The dynamic viscoelasticity of the test materials was evaluated by the air-coupled ultrasonic trammission method and air-coupled ultrasonic surface method, and the evaluation results of dynamic viscoelasticity of carbon fiber composites were obtained. Experimental results shows that the air-coupled ultrasonic trammission method can be used to evaluate the dynamic viscoelastic of the composites, but the air-coupled ultrasonic surface method can only be used to evaluate the dynamic viscoelasticity of the surface material of the composite,the dynamic viscoelasticity of the whole composite can not be evaluated.The work that completed in this paper has laid a good foundation for the nondestructive evaluation technology of the dynamic viscoelasticity of the composites.