Yuwen Qin

The study and application of a new filtering method on electronic speckle pattern interferometric fringe

It is important for the study of digital image processing to remove noises and enhance images because of various noises in images. The article is concerned with the recursive algorithm-filtering technique, which is capable of effectively removing noise and rapidly leading to a continuous gray-level distribution of a random image. By applying the method on speckle images of defects of rubber material, it is shown that this technique is the most effective and speedy method for the filtering of ESPI fringe patterns. Comparing the images before and after filtering, we can see the advantages of the novel technique clearly. It can increase the accuracy of measurement both in phase measurement and in quantitative evaluations of defects.

Infrared thermography and its application in the NDT of sandwich structures

Abstract Thermographic nondestructive testing (NDT) based on the thermal resistance effect of defects is developed for the inspection of delaminated and sandwiched defects embedded in composite structures. The resolution is examined for artificial delaminated defects in carbon-fiber honeycomb structures using conventional infrared radiation heating. The experimental results have demonstrated that radiation heating is effective for revealing defects in the composite structures. An experimental and computational hybrid system is developed for detecting defects in various composite structures. The system consists of an infrared thermal video system which measures the surface temperature distribution of the structure, a computer with a PIP-1024B image board which performs image processing of thermograms, and a HP ink jet XL printer. It is found that this system is readily applicable to the detection of defects located at the interface of the core and skin in honeycomb structures and delaminations in composite materials.

Determination of residual stresses using large shearing speckle interferometry and the hole drilling method

An experimental method is described which can measure the directions and magnitudes of residual stresses in metal. The method uses large shearing speckle interferometry combined with the hole drilling method to measure the surface deformation around the hole. For one-dimensional tension, the experimental results for the surface residual stresses are obtained and they agree very well with theoretical predictions. In addition, two-dimensional residual stresses on the actual structure surface are also measured.

Experimental investigation of micromechanical behavior of advanced materials by moiré interferometry

Several typical instances show that moire interferometry is an effective experimental method for micromechanics study of advanced materials. By using moire interferometry, stress-induced martensitic transformation plastic zone in ceria-stabilized tetragonal zirconia polycrystalline ceramics (Ce-TZP) is studied. The experimental results show that the stress-induced transformation at room temperature is not uniform within the transformation zone and the phenomenon of microscopic plastic flow localization for transformation is revealed. Meanwhile, the experimental investigation of the pseudoelasticity behavior of Cu-Zn-Al polycrystalline shape memory alloy and bending behavior of carbon-fiber aluminium laminates (CALL) are reported. The experiments reveal some important features of the deformation processes of the materials. Finally, the measuring ability of moire interferometry for micromechanics study is discussed.

The research in image distinction for isodyne patterns

Abstract A new birefringent phase shift method applied in isodyne fringe pattern distinction is developed. The phase map obtained by the new method corresponds to the isodyne surface in whole fields. The theory and technique of the new method is described and a bimaterial beam under three-point bending is studied as an example.

Novel quantitative non-destructive testing method for composite structures

A novel QNDT (quantitative non-destructive testing) method is developed that is combined with a phase-shifting shearing speckle and thermograph, and, it aims at the detection of faults such as cracks, voids, delamination and weak areas. The technique is immune to ambient noise and is suitable for measuring the in situ environment. Some different depth defects that would produce deformation differing from other positions could be found with shearing speckle when the sample is loaded, however, a thermograph based on the thermal resistance effect of a defect can detect only those varisized defects embedded deeply in the composite structure by measuring the surface temperature distribution. The resolution is examined for artificial delaminated defects in carbon-fiber composite structures using a phase-shifting shearing speckle and thermograph. The experimental results have demonstrated that the technique is effective for revealing defects in composite structures.

Marking-dots digital image correlation and application to studies of spinal biomechanics

A method of marking-dots digital image correlation is developed to measure the biomechanics behavior of cattle spine. In the system, a video camera and personal computer are used to acquire digitized images of a random speckle pattern on the surface of a marking-dot before and after deformation. The method of making-dots digital image correlation can immediately measure the transformation by tracking the gray value pattern in small local neighborhoods commonly referred to as subsets. In the experiment, a specimen was selected from the cattles spine that was covered with some muscles and tissues. It is apparent that the covering muscles and tissues cannot be treated as the information carrier, for they must be kept active and moist curing by the physiological brine in the course of the experiment. In order to solve the problem, the marking-dots were fixed into the vertebrae, and the front surface of a marking-dot was coated with a thin layer of white paint and splattered with black spot so as to create a random black-on-white speckle pattern. Experimental results have shown that the marking-dots digital image correlation method can be applied to the measurement of the biomechanical behavior of cattle spine, and offer an effective measurement tool to research the range of motion of the adjacent segment in spine under intervertebral fusion.

New approach to filtering on electronic speckle pattern interferometric fringe images

The recursive filtering algorithm, a simpler method of filtering for electronic speckle pattern interferometry (ESPI) images, is presented and studied in the paper. In pace with the new method, the applied software is developed specially. By experimental demonstration, it shows that the technique is the most effective and speedy method for the filtering of ESPI fringe patterns so far. Comparing with the images before and after filtering, we can see these advantages of the novel technique clearly.

Real-time interval technique for electronic shearing speckle pattern interferometry

Abstract Electronic shearing speckle pattern interferometry (ESSPI) is a new approach in photomechanics, which has played a special role in the stress/strain analysis and nondestructive testing (NDT). This paper presents a novel technique, the real-time interval technique of ESSPI, which makes it possible to study the continuous deformation in an object to be tested. The theoretical analysis and experimental results are given, which show that the technique is also a very convenient and quick method for NDT.

Digital image correlation for mechanical behavior of viscoelastic materials

A digital image correlation system, which is a combination of a long-focus microscope and a digital image-measuring device, is developed for study in the mechanical behavior of the viscoelastic materials. In this paper, the precision of the digital image correlation system is assessed by using an extra solution within of the framework of infinitesimal strain in particular, the choice of the size of subset in the correlation technique is discussed when the displacments are not infinitesimal. Then, the system is employed to obtain the displacement field in each step, strain field in the interest area of the specimen, and the experimental result show that digital image correlation system can perform the precise measurements of the mechancial behavior of viscoelastic materials.