Damage Detection In CFRP-GFRP Composite Bar Using Guided Ultrasonic Waves

In the long-term use of composite material rods,aging and fatigue damage will occur.The damage usually occurs in the interior of the structure and it is difficult to observe directly.If the stress-strain level and damage degree of the composite material sucker rod cannot be determined,structural failure,structural damage,etc.may be caused.The sucker rod is frequently replaced by the new one without detecting the actual rod body.The healthy state of the sucker rod will result in an enormous burden on economic costs.Ultrasonic guided wave based non-destructive testing method is currently the focus of research,has the characteristics of rapid detection,wide range,sensitive to damage,as well as simple equipment,low cost,etc.It can be detected without destroying the structure.Advances in technology can also be performed in situ on site,which greatly improves the effective utilization of the composite sucker rod.And it provides a basis for life assessment and failure early warning.And it is convenient for the detection of the health status of the sucker rod.In this paper,the ultrasonic guided wave detection methods are used for CFRPGFRP composite double-layers rods used as sucker rods.Meanwhile the environmental aging damage and fatigue damage are studied.The main research contents are as follows:(1)For the double-layers of CFRP-GFRP composites which is treated as anisotropic materials,the research of ultrasonic guided wave has been theoretically analyzed.According to the characteristics of the guided waves in the transversely isotropic cylindrical shell,the multi-layers have been regarded as infinitesimal dividing model.The assumption of guided wave propagation in the structure is also demonstrated in the experiment.(2)According to the working characteristics of piezoelectric wafers,its simplified linear model of effective force is applied to the composite multilayer structure,which can excite and receive guided wave signals in different material layers of the structure.When in the different layers of the structure,the piezoelectric wafers can receive different signals,indicating the different types of damage.(3)Ageing test and fatigue test of CFRP-GFRP composite double-layers rods were carried out.The signal amplitude and travel time were used as evaluation indexes.And the indexes were used to distinguish and identify the different degrees of damage patterns that appeared in the aging test and fatigue test.(4)Explain the failure modes under the three load levels in the fatigue test.Correspond to the signal characteristics of the guided wave propagation for the internal structural damage under different loads,it can be used as detection which is in situ on site.The state of health and whether it has reached the serviceability limit.And it can be the judgment for structural failure and destruction.