Defect Detection Sensitivity Research Articles

Enhancement of acoustic imaging of polymers by cooling

A low temperature acoustic imaging technique is proposed to enhance the sensitivity of defect detection in materials with highly temperature dependent acoustic properties. An acoustic imaging device has been developed where the sample temperature is precisely controlled between 30 and −94°C using a methanol coupler. To illustrate both the feasibility and advantages of this method, a bonded structure using bisphenol ether type epoxy resin was observed; and defects and non-uniform structure not visible at ambient temperature became apparent in 25 MHz acoustic images when the sample was cooled to −30°C. From measurements of velocity and attenuation, this improvement was ascribed primarily to a decrease in the attenuation loss within the epoxy resin. The use of phased arrays and non-destructive evaluation of fibre-reinforced plastics are also discussed.

NDT by speckle rotational shear interferometry

Speckle rotational shear interferometry has been used for NDT of diffuse objects. Shear is obtained by placing a pair of Dove prisms before a double aperture arrangement. For centrosymmetric objects, defects appear in a fringe-free field when shear is introduced about the centre, unlike other shear techniques where defects appear in a parent fringe structure. Furthermore, by eccentric loading and rotational shear applied about the centre, sensitivity for defect detection can be enhanced. A qualitative theory and experimental results are presented.

Detectabilyty of fatigue crack growth by ultrasonic testing. Development of multi-probe.

There are many methods for measuring the depth of fatigue crack by ultrasonic testing. The flaw heights are measured by ultrasonic angle beam testing. This method has various problems. For example, pulse amplitude is affected by flaw size and the inclination of a flaw. This time, the authors developed a special probe. This work has been carried out to investigate the flaw detection sensitivity of the probe. The results indicate that the probe can estimate fatigue crack depth in an accuracy of 0.52.0 mm.

Rotational-shearing interferometric characterization of inertial fusion targets

Inertial fusion targets have strict requirements on sphericity, surface smoothness, and layer thickness uniformity. Interferometric characterization techniques have been extensively used to measure target quality. An imperfect target, which can be described as a superposition of defect components on a perfect shell, produces an interferogram with the defect and perfect shell components combined. Separation of the defect-produced components in a target interferogram from the concentric fringe pattern produced by a perfect target is often difficult and limits precise interpretation of the target defects. We have utilized the rotational symmetry of a perfect target to improve defect detection sensitivity by using rotational-shearing interferometry. One advantage of this approach is that rotationally symmetric objects are in phase, making only the nonrotationally symmetric defects visible. Another advantage is that shell nonconcentricity can be measured independently of shell thickness. We have developed a simple analytical model which describes the interferometer’s operation and constructed and tested a prototype device for fusion target characterization.

Industrial radiography and the linear accelerator

To obtain maximum sensitivity of flaw detection in the radiographic examination of thick specimens encountered in heavy engineering, several aspects of the X-ray equipment must be considered. The most important factors are the energy of the radiation and the size of the source, while in order to obtain reasonably short exposure times a large X-ray output is required.The paper shows that, due to the complex process involved, the absorption of radiation at first decreases as energy is increased, but reaches a minimum and thereafter rises to some asymptotic value. The energy for minimum absorption depends on the absorbing substance, but for the materials used in engineering it will be some few MeV. Since the inherent unsharpness of the photographic image increases with energy, it can be shown that optimum results may be expected with equipment operating at an energy of the order of 4 MeV.The development of the travelling wave linear accelerator, which is briefly described, has made possible compact equipments to operate at such an energy, and the results of investigations into the suitability of such equipments for industrial radiography are given.