Study Of The Creep Behavior And The Nondestructive Fault Detection Of The Sandwich Panel Flexural Members

As a kind of new-style building insulation materials, sandwich panel is increasingly widely applied in all kinds of industrial and civil architecture. However, due to the lack of the long-term capacity research of the sandwich panel, the promotion of the sandwich panel and the development of the related manufacturers are seriously hindered. Considering this, this paper studied the long-term capacity of the sandwich panel from two aspects.Firstly, through the core material creep test we got the creep characteristics of the sandwich panel core material under the long-term load, verified that, the shear modulus and the elastic modulus holds a time-varying relationship. The six-parameter-Burgers model was used to identify the shear modulus curve; the constitutive equation of the Burgers model is derived, and then the mathematical software– Matlab is applied to fit the shear modulus curve to get the value of the model-parameters. Then the shear-relaxation modulus of the Burgers model is written in the form of Prony series, the parameters of the shear-relaxation modulus was got and substituted into the finite element software to simulate the creep behavior of the whole sandwich panel and analyze the creep properties of the sandwich panel. Then, the simulated results were compared with the experimental results to verify the correctness of the theory and the rationality of the model. Lastly, the influences of the thickness of the core material and the faceplate to the creep properties and long-term capacity of the sandwich panel were analyzed.Secondly, the ultrasonic non-destructive testing method was used to detect the possible injury of sandwich panel in normal use, and the stein unbiased risk estimation method of the wavelet analysis technique was used to determine the threshold value to precede a soft threshold de-noising treatment to the ultrasonic echo signal, then the de-noised ultrasonic echo signal was decomposed and the local modulus maxima of each layer was got. The results show that: after wavelet de-noising and wavelet decomposition, identifying the arrival time of the reflected echo signal and the change of the various layers'waveform of the wavelet decomposition, the ultrasonic non-destructive testing method can effectively identify various types of damage.