Abstract: The strength of a green compacts formed through warm powder compaction route is strongly dependent on the forming load and temperature. As the forming load increases, the powder particles move from its initial position by sliding among them and die wall. This movement results in new arrangement and packing order of the particles. However, due to this movement, pores among the particles are generated that affects the mechanical properties of the green compacts. Having pores in green compacts lead to strain intensification at ligaments between pores during sintering at later stage, hence serve as areas for crack initiation. Therefore, as the powder forming relates directly to the load and temperature, strength to porosity relationship has to be analyzed based on those parameters. This paper presents the effect of porosity to the strength of green compacts formed at different load and temperature (70 kN to 130 kN; 30°C to 200°C). The bending strengths of green compacts are measured while Scanning Electron Microscopy is used for porosity evaluation. It has been found from the results that porosity and strength are related to each other at all forming parameters. In addition, high forming load and temperature give better strength due to porosity reduction.
Abstract: Moiré grating is a basic optical component, and can be used in various moiré methods. The conventional grating fabrication technology is based on photolithography and holographic interferometry, however, it requires complex optical components and is very difficult to put into practice. In this study, nanoimprint lithography (NIL), or rather, hot embossing lithography (HEL), is proposed for producing high frequency grating. Compared with silicon mold, holographic moiré grating mold costs less and is not easy to break, thus is chosen to be the mold in HEL. Using this mold and the hot embossing system, the grating structure can be transferred to the polymer after HEL process. Through a number of experiments, the process parameters were optimized and gratings were successfully fabricated. The multi-scale morphology of the fabricated gratings was then characterized by scanning electron microscope (SEM), atomic force microscope (AFM) and moiré interferometry. The microscale images observed by AFM and SEM show the regulate dots with equal spacing and the macroscale moiré patterns illuminate the excellent qualities of fabricated grating in a large area. The successful experimental results demonstrate the feasibility of the grating fabricated by HEL for the moiré measurement.
Abstract: This paper describes a quantitative damage identification method for CF/EP composite laminates based on Lamb waves excited by distributed PZT wafers. The fundamental symmetric mode S0 is considered to detect defects (hole) in the plate. The Morlet wavelet and the cross-correlation analysis are introduced as signal processing tools for determining the time-of-flight (ToF) of Lamb wave. Considering the difference of Lamb wave velocities in different directions in a composite plate, the relationship of Lamb wave velocity in a unidirectional fibre reinforced laminate is studied and validated experimentally and numerically. In addition, a defect identification approach is revealed based on a regular arrangement of PZT wafers. Then, on the basis of the relationship of the wave velocity and the ToF, the location of a hole is identified by proposed method. Results demonstrate that the method is feasible in quantitative diagnosis of composite structures.
Abstract: The bending fatigue of Al6061 alloy has been evaluated by the acoustic nonlinearity of laser-generated surface wave. The surface wave is very attractive for field applications since it enables to pulse and receive signals at the same surface of materials, and has strong acoustic nonlinear effects on the surface. A relative acoustic nonlinear parameter was measured successfully on the surface of fatigue-damaged aluminum 6061 alloy. The results show that the acoustic nonlinear parameter increased with fatigue damage accumulation in relation to dislocation evolution. Consequently, this study suggests that the acoustic nonlinearity technique of a laser-generated surface wave can be potentially used to characterize surface damage resulting from bending fatigue.
Abstract: Pure calcium phosphate and ZrO2 doped calcium phosphate biomaterials were synthesized using an organic based phosphoric acid (DEHPA) as its starting material. The precipitated products obtained from the sol-gel reaction were then used to compare the phase transformation using in-situ XRD. The study shows that amongst the notable difference between these two samples is that the ZrO2 doped calcium phosphate tends to form the β-Ca(PO3)2, β-TCP and HA phases at lower heating temperatures compared to the pure calcium phosphate. Another major different seen in the phase transformation of the ZrO2 doped calcium phosphate is the transformation of β-TCP into HA before it leads to the formation of α-TCP at higher temperatures.
Abstract: A sharply notched specimen of porous silicon carbide with porosity of 37% was fatigued under four-point bending. The opening displacement of a fatigue crack was measured at several positions along cracks by using scanning electron microscopy. The crack propagation curve was divided into stages I, II, and III. The crack propagation rate first decreased with crack extension in stage I and became constant in stage II. In stage III, the crack propagation rate increased again. The range of crack opening displacement measured in SEM was lower than that calculated from the applied load range by FEM, suggesting that the anomalous variation of the crack propagation rate with crack extension was caused by crack-tip shielding due to crack face contact. The crack-tip stress intensity factor was estimated as a true crack driving force from the relation between the crack opening displacement and the applied load. The amount of crack-tip shielding increased very quickly with crack extension, reducing the crack-tip stress intensity factor in stage I. In stage II, the increasing applied stress intensity factor is balanced by the increase in the crack-tip shielding. The crack-tip stress intensity factor increases with crack extension in stage III.
Abstract: Nondestructive testing (NDT) is an important tool in the world of industry. Among different NDT methods, radiography plays a very interesting role both in industry and medicine. Medical and industrial uses of X and gamma rays were recognized since more than 1 century ago. One of the interesting uses of radiography is in archeological and art applications. In this research, radiography was utilized for identification of a damaged art-historical material. The subject is a brass tray belonging to Iran cultural heritage with an estimated age of about 3500 years. The tray was found in Lorestan province and referred to as “Lorestan bonze”. The object was damaged seriously due to heavy corrosion attack. Therefore recognition of the object was a major problem. Normal radiography method can help for object determination, but it suffers some major drawbacks related to contrast and thickness measurement. Image processing technique and a precise thickness measurement method were added to digitized radiographs. A precise radiographic thickness method was introduced and used before for the pipeline radiography. For digital image processing, Canny edge detection method and Gaussian filter were used. Radiography image obtained from this work showed a very clear picture of the original trace of hammered design. These results showed that a combination of radiography, image processing techniques and consideration of physical principles of radiation interaction with materials can produce a very clear image which can be used effectively for hte detail analysis of cultural heritages.
Abstract: Gamma-ray computed tomography (CT) is a powerful non-invasive imaging technique for viewing an object in 2-D or 3-D cross-section images without the need to physically section it. The invention of CT technique revolutionised the field of medical diagnostic imaging because it provides more detailed and useful information than any previous non-invasive imaging technique. The method is increasingly used in industrial fields. This paper describes the development of a gamma-ray computed tomography system for imaging and visualising of industrial multiphase reactors. The theoretical aspects of CT scanner, the system configurations and the adopted algorithm for image reconstruction are discussed. Penetrating radiation from an isotopic gamma-ray source of Cs-137 and a bank of NaI(Tl) scintillation detectors in combination with a dedicated mechanical gantry set-up were used to construct the CT system. During scanning, the movement of the detector’s bank and rotation table is controlled by a LabView-based software. The software is also designed to control all associated nuclear electronics equipments and finally to acquire gamma-ray transmission data. The image reconstruction is performed by using Expectation-Maximisation (EM) and Alternating-Maximisation (AM) algorithms written in Visual-Fortran programming language. Several physical phantoms to simulate industrial multiphase process columns and reactors were scanned using this CT scanner. Some of the reconstructed images are presented in this paper.
Abstract: Sampling Moire method is one of the convenient phase analysis methods. The accuracy of phase difference analysis is from 1/100 to 1/1000 of the grating pitches. This method is useful for a real-time measurement because the phase analysis can be performed from a single-shot image. In this paper, we developed a sampling moire camera which can analyze grating phase in real time. This camera is composed of a CMOS sensor and a FPGA. A two-dimensional grating image taken by the CMOS sensor was analyzed by the FPGA in real time. An application on a real-time deformation measurement of a cantilever is demonstrated.