Papers by Keyword: Imaging Technique

Abstract: This study presents the characterisation of the air voids distribution for porous asphalt mixtures compacted using gyratory compactor. The distribution of voids content and voids shape within the porous asphalt were characterised for different nominal maximum aggregate size (NMAS) and specimen height. This is to evaluate the effect of different aggregate size composition and lift thickness on the air voids characteristics of the compacted porous asphalt. Two types of gradations were adopted i.e. Grading A (with NMAS=10 mm) and Grading B (with NMAS=14 mm) and they were fabricated for two different heights (50 and 100 mm). The internal structure was captured using X-ray Computed Tomography and image analysis techniques were used to process and analyse the images. It was found that mixture with coarse aggregate gradation produced larger void size with an elongated shape, which indicates voids connectivity within the mixture compared to fine gradation with more circular and smaller void size.For lift thickness, itacts differentlyfor different aggregate gradations. The specimen produced greater voids connectivity when the fine and coarse gradations were compacted at 100 mm and 50 mm respectively. These show that NMAS and lift thickness influence the mobility of the aggregate particles during compaction which affect the voids formation and determine the effectiveness of the compaction.

Abstract: The atomic force microscope (AFM) is a mechanical imaging instrument that measures the three dimensional topography at nanoscale as well as physical properties of a surface with a sharpened tip. This paper proposes an AFM imaging process for obtaining quality images in order to describe surface topography of different materials. Good topography information is a premise in nanoindentetion and in determining mechanical properties of materials. Samples used were: copper, nickel, titanium, polyamide and trabecular bone.

Abstract: The objective of this work was to demonstrate the feasibility of nonlinear vibration/acoustic/ultrasonic diagnostic tools to be implemented in a structural health monitoring system for imaging damage. In particular, the sensitivity a second harmonic imaging technique (SHIT) based on material nonlinear elastic effect known as second harmonic generation (SHG) was investigated. Examples of the capability and limitations of the proposed damage detection process to detect and image barely visible impact damage (BVID) due to low velocity impact (<12J) are presented for various composite laminated. The presence of microcracks, debonding, delamination, etc… could induce the material to behave in a nonlinear elastic fashion and it is highlighted by the presence and amplitude of harmonics in the spectrum of the received signal. The results showed that the proposed SNIT methods appear to be highly accurate in assessing the presence and magnitude of damage with very promising future NDT and structural health monitoring applications. Moreover the technique was validated with two conventional NDT techniques: pulse thermography and thermosonic. The first failed in detecting the damage on the impact face, but delamination on back surface was localized. The second technique was capable of localising and quantifying the damage on the impacted surface agreeing well the results obtained using non linear method.