Papers by Keyword: High-Speed Photography

Abstract: A novel experimental method has been developed to evaluate the mode I crack growth behavior of adhesively bonded joints under impact loading. The split Hopkinson pressure bar (SHPB) technique and the digital image correlation (DIC) technique was employed to evaluate the crack growth behavior. To reduce the dynamic effects by controlling loading input of the SHPB apparatus, the fracture toughness was determined precisely based on static evaluation formula. To contrive the testing set-up, high loading rate was kept until the arrest of crack. The fracture toughness of titanium alloy/epoxy adhesively bonded joints during crack propagation was obtained successfully by using present method.

Abstract: In order to measure the displacement and strain field in the fatigue crack tip area of CT specimens under high frequency resonant loading condition in the fatigue crack propagation test, a method based on the digital image correlation (DIC) and digital high-speed photography technology are proposed in this paper. First, a series of digital speckle images of CT specimen under sinusoidal alternating load were collected by digital high-speed photography equipment, the displacement and strain fields within the region of crack tip in each image were calculated by DIC. The sinusoidal changing strain curve has been obtained by the least square sine wave fitting method, and the characteristic parameters of sinusoidal strain are calculated, such as the amplitude, frequency, phase, mean load . The images of characteristic position in one stress cycle were obtained by comparing the fitted sine curve of strain with the corresponding speckle images. Finally, the dynamic strain gauge was used to measure the strain at crack tip point during one stress cycle, and the accuracy and feasibility of DIC method were verified by the experimental results. The study result presented in this paper will supply a foundation for exploring the crack propagation law and measuring the fatigue crack growth parameters under high frequency resonant loading condition further.

Abstract: Experimental study on macroscopic spray characteristics of a certain type of domestic common rail injectors under the conditions of different injection pressures was carried out through a high-speed digital camera. Furthermore, a fuel dripping phenomenon at the end stage of injection was observed through the high-speed digital camera equipped with a long-distance microscope, and a further analysis of the phenomenon was made. The results show the increase in the injection pressure can evidently enhance spray cone angle and expand the scope of spray field in combustion chamber, which is conducive to air-fuel mixture. The spray cone angle during the development spray shows a double-peak shape. And the long response-time of seating of solenoid valve core that disables the injection cutting off in time is one of factors causing fuel dripping phenomenon.

Abstract: A novel high-speed photography is introduced to determine the critical fracture strain of a near alpha titanium ally during hot compression deformation. This method precisely captures the nucleation site and propagation process of cracking, and thus is an excellent method to represent dynamically the hot-deformation fracture. Compared with the traditional way, it can significantly decrease the number of trials and improve the accuracy. Based on this method, the critical fracture strain is measured, and a critical fracture model is developed.

Abstract: An experimental investigation into projectile penetration of pre-tensioned woven fabric samples – Tawron^® CT 717 (plain weave) – is undertaken. Specimens are clamped at their top and bottom edges, and pre-stretched by forces of 200N, 1000N, 2000N, 3000N and 4000N respectively. They are then oriented at various angles (0, 7.5°, 15° and 30°) from the vertical (perpendicular to the horizontal axis of a gas gun), and subjected to impact by a 12mm diameter steel sphere. A high-speed camera is utilized to observe the deformation and failure of the fabric, and to determine the residual projectile velocity. For normal incidence, the ballistic limit initially increases, then decreases with pre-tension, displaying a maximum resistance for a pre-tension of about 2000N. With respect to the angle of incidence (obliquity of impact), for target inclinations of 7.5° and 15°, pre-tension has minimal influence on the ballistic limit, while for an inclination of 30°, the effect of pre-tension on the ballistic limit is similar to that for normal impact.

Abstract: Based on the chaos theory and related algorithm, largest Lyapunov analysis of current of laser-twin-wire pulse MIG welding process are performed from the point of view of nonlinear time sequence. Largest Lyapunov exponent (LLE) of characteristic current under different laser power were calculated, meanwhile synchronous high-speed photography was adopted to observe arc shape and droplet transfer. The results indicate that arc shape and the force state of droplets changes as a result of interactions between laser plasma and arc plasma. Addition of low power laser intensifies the interplay of two arcs, which decreases the stability of welding process. When laser power reaches to a certain extent, a stable cathod spot and a conductive channel are obtained for arcs. Stable welding process and small welding spatter are acquired.

Abstract: Hydrodynamic information of the flow occurring as a bubble ruptures at a gas liquid interface has being obtained from computer simulations. The simulation result is verified by conducting high-speed photography experiment. Process of bubble rupture is clearly captured with simulation and experiment. Shear force generated by bubble rupture increases along with decrease of bursting bubble diameter or increase of coefficient of surface tension. The maximum average shear force ranges from 0.97Pa to 1.91Pa, when bursting bubble diameter changes from 2mm to 10mm.

Abstract: In order to do research on the motion time of plasma spray gun in powder particle flame plating, the paper made an analog computation to powder particle motion process of plasma spray gun by establishing powder particle equation of motion and thermal evolution equation, after that the motion time of powder particle in electric arc was obtained. It provided advantageous theoretical basis for plasma spray gun design after confirming the computation results by making use of high-speed photography technology.

Abstract: The experiments of artificial heart valves were divided into in vivo and in vitro experiments; in vivo experiments provide accurate experimental parameters serving in vitro research. Simulation experiment used in vitro usually goes like this, firstly design a similar model or prototype phenomenon, then analysis the model working out the regular parameters related to the process, ruled out the possibility of impact on the study of individual exist in vivo experiment. In vitro experiments are likely designed; performance can be simplified and prominently concerned about contents, even designed some extreme conditions to test. A number of means related to fluid experimental measurement are included, such as the Particle Image Velocimetry（PIV）[1], Dual Catheter Method [2]，and ultrasonic method[3] and so on. However, these methods have different kinds of limitations, for example the Dual Catheter Method cannot be used as a routine determination for clinic due to its destructiveness, and PIV test requires expensive equipment. This study was designed by the image processing technology of high-speed photography aiming at the production of a reliable, simple, economic, injury-free and non-contact measurement method.

Abstract: In order to obtain the detonation front shape and spreading process of detonation wave, Rotating mirror multi-streak technique was used to shoot the detonation process of charge initiated from three points by high-speed photography technique. The record negative was read and these data were analyzed. The time differences of zero-time points and t-y coordinate curve were educed, and the chart of detonation wave shape was drew. The result provides a gist for warhead design. A method for analyzing and studying wave shape is offered.