Time Domain Acoustic Field Model Of Ultrasonic Propagation In Polymer And Full Spectrum Calculation Method

Ultrasonic testing is an important branch of non-destructive testing technology,which serves a new idea and approach for on-line and non-destructive characterization of polymer.This paper presents a time-domain ultrasonic model for measuring multi-layer polymers,a full spectrum calculation method for measuring ultrasonic parameters and a mathematical model for characterizing degree of orientation via velocity of longitudinal wave.There methods were applied to different polymers.This paper obtained following achievements:1.A time-domain model for measuring multi-layer polymers was built.Considering the phenomena of reflection,transmission and attenuation during ultrasonic propagation,a time-domain model was built,which can be used to simulate reflected signals.Objective functions were employed to describe the similarity between the calculated signals and the measured signals.By solving a multi-objective optimization problem,the optimum parameters of each layer and layer thickness can be obtained.The proposed model was used to measure layer thicknesses of water-assisted co-injection molding products.2.A full spectrum analysis method for measuring ultrasonic parameters was proposed.Reflected signals from the upper and lower surfaces of the polymeric materials are connected by a frequency dependent transfer function.The logarithm of the transfer function can be linearly fitted,and the ultrasonic parameters including the ultrasound velocity and attenuation coefficient can be calculated from the vertical intercept and slope of the fitting line.The proposed method does not need to measure the thickness of the polymeric material and makes full use of data in measured waves.Experiments with various polymeric materials of different stiffnesses and thicknesses,as well as several influence factors including aluminum block and sampling frequency were carried out to verify the proposed method.Experimental results showed that the proposed method has high accuracy in measuring ultrasonic parameters.3.Comparison analysis and assessment for different ultrasonic velocity measurement methods were conducted.Pros and cons of time of flight method(TOF),water immersed method(UWI)and full spectrum analysis method(UFSA)were analyzed by a series of experiments.These methods were used to measure polymeric parts with different surface roughness.Combined with error analysis,the uncertainties of different measurement methods and their abilities of tolerating disturbance were discussed.Experimental results showed that when measuring polymeric parts with flat surfaces,the TOF and UWI method have higher accuracies;UWI and UFSA method are appropriate for measuring polymeric parts with rough surfaces;UFSA method has the ability of tolerating disturbance.4.A method for characterizing orientation structures via ultrasonic velocity was proposed.Based on ultrasonic wave equation and Boltzmann superposition principle,the relationship between ultrasonic velocity and degree of orientation was built and a method for characterizing orientation structures was proposed.2D-WAXD(2 Dimensional-Wide Angle X-ray Diffraction)experiments were carried out to investigate the orientation structures of TPEE(thermoplastic polyester elastomers).Impacts of injection velocity on the ultrasonic velocity of TPEE and degree of orientation were analyzed.Experimental results demonstrated that degree of orientation can be characterized by ultrasonic velocity.Achievements obtained by this paper provided a novel and accurate method for measuring ultrasonic parameters,realized the non-destructive measurement of layer thicknesses for co-injection molding products,and longitudinal wave velocity measurement method for characterizing polymer's orientation structure.These methods have important scientific significance and broad application prospect.