Noncollinear wave mixing for measurement of dynamic processes in polymers: Physical ageing in thermoplastics and epoxy cure

• Published in: Ultrasonics 2014-02, Vol.54 (2), p.684-693
• Main Authors: Demčenko, A., Koissin, V., Korneev, V.A.
• Format: Article
• Language: English
• Subjects: Aging; Curing; Elasticity Imaging Techniques - methods; Epoxy Compounds - chemistry; Epoxy Compounds - radiation effects; Epoxy cure; Hardness; Hot Temperature; Immersion; Materials Testing - methods; Monitoring; Non-linear ultrasonics; Nonlinear Dynamics; Nonlinearity; Physical ageing; Polymethyl Methacrylate - analysis; Polymethyl Methacrylate - chemistry; Polymethyl Methacrylate - radiation effects; Polymethyl methacrylates; Rheology - methods; Rheometry; Scanning; Thermoplastic resins; Ultrasonography - methods; Water - chemistry
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2013.09.011

•Physical ageing process was measured in two thermoplastics.•Epoxy cure process was measured with detection of time of: maximal viscosity, gel, vitrification.•Nonlinear ultrasonic technique is proved to be valid for these physical phenomena.•Procedure of selection of optimal conditions for wave mixing was presented. Elastic wave mixing using an immersion method has shown effective monitoring and scanning capabilities when applied to thermoplastic ageing, epoxy curing, and non-destructive testing. In water, excitation and reception of waves do not require physical contact between the tools and the specimen, making the acquisition of high-resolution C-scans possible. The nonlinear material parameters exhibit a much higher sensitivity to the specimen state compared to linear ones. Thus, the nonlinear data for polymethyl methacrylate (PMMA) have a 40% difference between zones of “young” and “aged” material, while the linear data show no difference at all. Methodology and logistics of the immersion wave-mixing method are discussed in detail. Monitoring of epoxy curing has also revealed a good sensitivity of the method to this complex process including several characteristic stages, such as the time of maximal viscosity, the gel time, and the vitrification time. These stages are independently verified in separate rheometry measurements. The presented method allows for a number of possibilities: wave-mode and frequency separations, elimination of surrounding medium influence, “steering” (scanning) a scattered wave, controlling the location of the intersection volume, single-sided or double-sided measurements, and operation in detector mode.