Jingwei Tong

Study on in-plane displacement measurement under impact loading using digital speckle pattern interferometry

A technique for measuring in-plane displacement under impact loading using digital speckle pattern interferometry (DSPI) is presented. To capture the speckle field produced by a ruby laser, an instantaneous digital image capturing system is proposed. Thus the dynamic speckle images can be recorded and stored in a digital frame store and the quality of speckle fringe patterns is improved using digital subtraction. As an example, the displacement field of a semi-infinite model under impact loading is measured. The results show agreement with those of the finite element method.

Deformation Measurement of Composite Laminate with Impact Damage under Compressive Loads

The out-of-plane displacement fields for a cross-ply laminate [03/903]s with impact damage under axial compression are investigated using carrier electronic speckle pattern interferometry (carrier-ESPI) in this paper. The compression after impact (CAI) test is conducted on rectangular specimen 65mm × 87.5mm in size using an anti-buckling fixture. In order to apply a uniform load to the top of composite laminate, a self-designed device insures that an accurate loading is given. The experimental results reveal the deformation characteristics of laminate under CAI test.

Study of dynamic displacement field measurement using DSPI

A technique for measuring in-place displacement under impact loading using digital speckle pattern interferometry (DSPI) with combining the digital subtraction and add mode is presented. A new technique of the add mode filtering is used. To grab the digital speckle of field produced by a pulse laser, an instantaneous digital image grabbing system is proposed. Thus the dynamic digital speckle image can be recorded and stored in a digital frame store. As an example, the displacement field of a semi-infinite model udner impact loading is measured.

Measurements of interlaminar deformation in the composite laminates

In this paper, an experiment is executed to analyze the displacement distribution of 56-ply composite laminates under three-point bending. In the experiment, the displacement fields on the two free edges of the laminated composite are measured by using the moire interferometry method and natural micro-image processing technique based on wavelet transform at the same time. In the first part of this study, a two-beam traditional moire interferometry experiment has been carried out. And in the second part, we present a new image processing method, which combines the theory of correlation and wavelet transform technique.

Vectorization system for interactive photoelastic image processing

Based on image and graphic technologies and synthesized preceding research achievements in the digital processing of photoelastic image, a vectorization system for interactive photoelastic image processing has been set up. The system consists of seven modules, and a toolbox. This paper describes the system structure, new techniques used in the system, and its features. By use of this system, the vectorized image files of the skeleton for stress analysis can be obtained. The application area of the system is wide, and it has quite strong interactive processing capability and user-friendly interface.

New method in experimental damage study of AS4/PEEK composite laminates

AS4/PEEK [0/+/- 45/90]7s composite laminates were subjected to a bending moment. We have obtained the displacement fields by moire interferometry with the aid of Long Distance Microscope. Based on wavelet analysis, the digital moire images were processed and analyzed. The special algorithms of unconstrained nonlinear minimization and the scale parameter were used to eliminate the influence of the noise in the digital image processing. Tension tests were carried out on AS4/PEEK [ 0/+/- 45/90 ]2s composites. When AS4/PEEK composite laminates were deformed, the images of natural surface of the AS4/PEEK specimen were recorded to study the damage initiation and growth. The experimental results show that the considerable interlaminal stresses between different plies, and these places were more prone to delaminate. The paper presents the microscopic damages and matrix crack growth observed by an optical microscope and the CCD camera.

Study of free edge effect on sub-laminar scale for thermoplastic composite laminates

The interlaminar deformation on the free edge surface in thermoplastic composite AS4/PEEK laminates under bending loading are studied by means of digital image correlation method (DICM) using a white-light industrial microscopic. During the test, any artificial stochastic spray is not applied to the specimen surface. In laminar scale, the interlaminare displacements of [0/90]3s laminate are measured. In sub-laminar scale, the tested area includes a limited number of fibers; the fiber is elastic with actual diameter about 7μm, and PEEK matrix has elastic-plastic behavior. The local mesoscopic fields of interlaminar displacement near the areas of fiber-matrix interface are obtained by DICM. The distributions of in-plane elastic-plastic stresses near the interlaminar interface between different layers are indirectly obtained using the coupling the results of DICM with finite element method. Based on above DICM experiments, the influences of random fiber distribution and the PEEK matrix ductility in sub-laminar scale on the ineterlaminar mesomechanical behavior are investigated. The experimental results in the present work are important for multi-scale theory and numerical analysis of interlaminar deformation and stresses in these composite laminates.

Application of twelve variables gradient method to the study of poly (β-hydroxybutyrate) crystallization

Poly(3-hydroxybutyrate) exhibits remarkable embrittlement upon storage at room temperature, and this problem limits its widely use in technical purpose. In this paper, morphology and micro-structure of PHB spherulite are investigated by using the twelve variables gradient method and polarization microscope. The results indicate that the PHB spherulites could continuously crystallize, namely: secondary crystallization, the morphology and micro-structure of PHB spherulite are changed, the embrittlement at room temperature was resulted from PHB secondary crystallization. Competition phenomenon in the process of PHB secondary crystallization was found.

Laser interferometric method for determination of elastoplastic strain field

A new full-field optical technique is developed to study surface deformation of solids. This method combines the measurement by grid method and the digital image processing. An optical information processing system and a digital image processing system of computer are used in this method. At the output plane we receive the pattern of grating lines taht can be used for the analysis of deformation of the specimen on which we have produced the phase grating. At last we show the application of this technique in the investigation of elastic-plastic fracture.

3D elastic-plastic analysis and experiment of free-edge effects in angle-ply thermoplastic composite laminates

The fully 3D orthotropic elastic-plastic analysis of interlaminar stresses and deformation for AS4/PEEK thermoplastic laminates is developed in this paper, and used to simulate the tensile stress- strain curves for (+/- 25)s4 laminates. Under uniaxial tensile loading, the 3D orthotropic elastic-plastic FE analysis and microscopic moire interferometry of interlaminar stresses and deformation are carried out for the (+/- 25)s4 laminates. It is found that the numerical tensile stress-strain curves of (+/- 25)s4 laminates agree with experimental. The numerical interlaminar displacement u and shear strain (gamma) xz are also consistent with the experimental results obtained by moire interferometry.