Papers by Keyword: Mechanics

Abstract: Teaching of science is an endeavor to translate abstract scientific concepts into the concrete ones which can be accessed by students. Among others, one practical method is the use of a hands-on model that allows students to manipulate materials and examine targeted phenomena. In this study, a hands-on model called “seesaw balancing” was proposed to demonstrating effects of “moment of force” in a classroom. By using the seesaw balancing as the main part of a structured inquiry activity, a single group pretest-posttest research design was employed in this study. With the purposive sampling technique, 50 grade 9th students who have never experienced in topic of moment of force participated in the study. The paired-sample t-test indicated a significant enhancement of students’ conceptual understanding after the treatment of structured inquiry laboratory at .05 significant level. Moreover, attitude questionnaire reveals the students have positive view towards the hands-on model as they perceived the model is interesting, suitable with the level of the students, help them to do self-learning, and safe to handle, respectively.

Abstract: The performance of metal matrix composites (MMCs) depends critically on the quality of the matrix-reinforcement interface. The nature of the interface in turn depends on the processing of the MMCs. At the micro-level, local concentration gradients around the reinforcement are being developed during processing and due to the metal matrix attempting to deform during deformation which can be very different to the nominal conditions. This plays a crucial role in the development of micro-structural events such as segregation and precipitation at the matrix-reinforcement interface. Micro-deformation characteristics of matrix reinforcement interface are modelled using commercial FE software and compared with analytical and experimental data. A method of calculation has been applied to predict the interfacial fracture strength of aluminium silicon carbide (Al-SiC) with 20% Vol fraction. Preliminary results show that the model succeeds in predicting the trends in relation to segregation and intergranular fracture strength behaviour in these materials. The proposed hypothesis will help the design engineers to select and use the materials in structural/load bearing applications. Interfacial strengthening characteristics will in turn give more accurate life predictions of such smart composite systems.

Abstract: The behavior of parts subjected to simultaneous thermal and mechanical fatigue loads is an area of research that carries great significance in the power generation, petrochemical, and aerospace industries. Machinery with expensive components undergo varying applications of force while exposed to variable temperature working fluids. An example case is found in steam turbines, which subject stainless steel blades to cyclic loads from rotation as well as the passing of heated gases. Accurate service life prediction is especially challenging due to the thermo-mechanical loading being present on the complex geometric profile of the blades. This research puts forth a method for determining crack initiation lifetimes in variably-notched type 304 austenitic stainless steel specimens subjected to differing fatigue and thermo-mechanical fatigue conditions. A base analytical model and genetic algorithm were used to develop phenomenology-informed predictions that fall within a factor of two of the actual crack initiation times.

Abstract: An experiment sturdy has been carried out for jet impingement cooling on the spherically convex surface is the development of mechanism. The effect of curvature, Space between jet exit and target surface, and Reynolds number on heat transfer is investigated for around air jet on hemispherical surface. The flow at the jet exit has fully developed velocity profile. A uniform heat flux boundary is created on the heated surface. The experiments are performed for 5000<Re<25000, 2<L/d<10, and jet diameters ranging from 1.3, 2.1, 3.4, 4.0 and 5.2 cm. In the mean time effect of curvature on local heat transfer is negligible at the wall jet region corresponding to r/d>0.5. From the experimental results the variation of the D/d ratio with local Nusselt number (Nu_st) for various Reynolds numbers and various L/d ratios are plotted. The results show that Nu_st increase with increase in curvature and the effect of the curvature will high at high Reynolds number. i.e. Nu_st at Re=25000 is 25% higher than at Re= 5000 This may be attributed to an increase in curvature increases acceleration, & size of three dimensional counter rotating vortices at stagnation point and the increment of Reynolds number increases the jet momentum, and also enhances the vortices creation. Nu_st is peaking in the L/d ratio of 6 because of high turbulence intensity as this distance.

Abstract: An active control test is done trying to control the vibration of gun tube. A four-layer piezoelectric actuator is glued on the root of an analogue tube (a steel barrel) and a voltage amplifier is used to regulate the voltage on the actuator restraining vibration of the barrel. With 130 voltages, the vibration acceleration of the simulated free end of the barrel decreases 83 percent from the original 60 m/s² and he attenuation time is shorted greatly. It can be seen that the vibration of the barrel is decreased obviously. It is feasible and very effective to control the vibration of gun tube by using intelligent structure according to the result of the theoretical analysis and test result.

Abstract: The antiriot shield is a type of individual protective equipment that was widely used in the process of dealing with the large-scale antiriots and unrests by the Armed Police Force. It has so many features that convenient for carrying and could effectively protect security for our majority officers and soldiers. However, the traditional riot shield has problem of smaller protection area. The paper is just aimed at solving this problem by using the three-dimensional mechanical designing software SolidWorks, having designed a new kind of automatically expanded riot shield which can be employed during in an emergency situation; the changes of this riot shield’s protection area could be realized by operators for controlling the automatically extended devices which were designed on the shield, this will effectively address the shortcomings that smaller protection area of the present shield, and it will provide a strong security for the majority of the Armed Police officers and soldiers in dealing with the large-scale mass incidents.

Abstract: The conveyer belt is a major component of the conveyor , whose cost accounted for half of the of the entire cost of the conveyor. The loss of the conveyor is mainly due to the use of friction and wear generated in the process, so study on the friction characteristics is very meaningful. The friction and wear of the conveyor is one of the factors affecting their life. Therefore, conducting applied research on belt conveyors and mechanical analysis becomes increasingly important. In this paper, some qualitative research on the mechanical properties is carried out, starting from the application of the conveyor belt.

Abstract: The gradient calcium phosphate bioceramic coating was produced on titanium alloy substrate by laser cladding. The microstructure, microhardness, fracture toughness, and residual stress of the tatanium-based gradient bioceramic composite coating were investigated. The results show that the microhardness gradually decreases with further depth increasing cross-section. The highest microhardness of the coating and the transition layer is 1544HV and 1160HV, respectively. The fracture toughness K_IC is 3.72±0.03 MPa·m^1/2 of bioceramic coating and 4.55±0.02 MPa·m^1/2 of the transition layer, which is closely resembles the human compact bone. Furthermore, the residual stress gradually decreases from the coating to substrate, which is 221MPa between ceramic layer and the transition layer and 108MPa between the transition layer and substrate. This distribution is conforms to gradient composition design, which reducing harm of the specimen deformation and cracking.

Abstract: Architectures of fault systems play important role in stability and mechanics of rock mass. While growth mechanism of faults is intrinsic controler for architectures of fault systems. This paper presents a case on faulting in the dam area of an oversized hydropower in Southwestern China. The faults in this area are mostly strike-slip faults with shallow brittle deformation characters, extending tens to hundreds of meters. These faults can be divided into four groups which are formed during two generations corresponds to two periods of tectonic events. Growth model of these faults have been built based on geologic and mechanic data. The first generation of faults was formed based on preexisting joints. While the secondary generation emerge only if the existing faults become critically misaligned during rotation of the primary stresses. The criterion laws for formation of secondary faults are suggested. According to the growth model, we can predict placement of secondary faults in space. Conversely, when geometry and space characters of the fault systems are known, we can estimate mechanic parameters and tectonic environments of the rock mass.

Abstract: In this paper, combining with the domestic design and application of the snowplow in quality and quantity two aspects, basing on engineering application software ADAMS and CATIA, dynamics for 10t snowplow working device was researched, and the strength of the main stress components was analyzed by finite element method. On the basis of lightweight, strength and structure reasonable design, the snowplow device structure was verified feasibility through the research results. The paper studies could have a certain theoretical reference for the theoretical design and practical application of similar products.