Laser forming is a modern metal forming method in which no mechanical force is needed. In this paper, numerical and experimental approaches to this phenomenon on were conducted. Numerical method comprised of couple heat-displacement. In it, heat flux distribution of laser beam was applied on the steel layer in Gaussian form and by using subroutine code writing procedure. Experimental tests were conducted by using Nd: YAG laser with maximum power of 300 watts and on a bi-layer Fe/Al work piece. The result of bending angle at different laser power ranges indicated that bending angle increases occur as this parameter is increased.
In this paper, an analytical method is proposed for calculation of natural frequencies of a delaminated composite beam from both free and constrained mode frequencies. In previous studies, the frequencies of a delaminated composite beam were computed with assumption of occurring open or close delamination during the vibration. According to this assumption, two separated modes, i.e., “free mode” and “constrained mode”, are occurred in vibration of the delaminated beam. In fact, a delamination may breathe (open and close) during the vibration and the assumptions of the free or constrained mode models are not completely correct in the whole of the vibration period. For this reason, a new formulation is proposed for calculation of natural frequencies based on the breathing of delamination. The obtained results are compared with various theoretical and experimental results available in the literature. Thus, the effects of location and size of delamination can be investigated on the natural frequencies of delaminated beams.
In this paper, a simplified method is proposed for deriving equilibrium equations in continuous systems. The new method is indeed the direct applying of Newton’s laws on free body diagram of point. First, by describing the concept of equilibrium equations and investigating the differences between concentrated masses and continuous systems, the physical basis of new method is introduced. It is shown that, using intensive properties simplifies the analysis of continuous systems. For verifying the new method, the governing equations in Cartesian, polar and spherical coordinates systems are derived. We have to consider nonlinear terms due to developing large slopes in system. Hence, nonlinear governing equations in Cartesian system are derived too. Finally by noting to the simplicity of new method and its independency from complicated differential and vector analysis in other methods such as Hamiltonian and classic methods, the interests of new method are emphasized. By knowing concept of physical point, a united process is accessible which is extendable to other governing equations of continuous systems.
Silicon/glass bi-materials are used in micro-assembly and packaging of micro-electromechanical systems (MEMS) and micro-electronics devices. In this paper, maximum tangential stress (MTS) concept is used for determination of the fracture initiation angles of silicon/ glass bi-material notches. First, the MTS criterion is analytically formulated for a bi-material notch problem. Then, the criterion used for prediction of fracture initiation angles of some experimental data given in literature for silicon/ glass bi-material notches. In addition, the modified MTS (MMTS) criterion, which considers the effect of I-stress, was compared with the MTS criterion and the experimental data. It was shown that MMTS criterion provides more accurate results than the MTS criterion for estimation of the fracture initiation angle.
Stroke is one of the main causes of disability. It affects millions of people worldwide. One symptom of stroke is disabled arm function. Restoration of arm function is necessary to resuming activities of daily living (ADL). Along with traditional rehabilitation techniques, robot-aided therapy has emerged recently. The control schemes of rehabilitation robots are designed for two reasons. First they are designed for passive rehabilitation in which the robot guides the patient & apos; s limb through a predefined path and second for active rehabilitation in which the patient initiates the movement and is partially assisted or resisted by the robotic device. This paper introduces a new robot for shoulder rehabilitation. The Shoulder Rehabilitation System (SRS) has three degrees of freedom (DOFs) for three rotational DOFs of the shoulder but additional translational DOFs of the shoulder are also allowed to avoid discomfort to the patient. A new open circular mechanism is proposed for the third joint that solves the known issues for rehabilitation robots such as long wiring and discomfort associated with closed mechanisms. Lyapunov-based controller with integral action is proposed to guide the robot through a predefined trajectory. Simulation results proved that the proposed controller can track the desired trajectory; reject constant bounded disturbance to the system and is robust due to its nonlinear nature. The proposed controller is designed to be used in passive rehabilitation.
This work is devoted to the experimental study of a glass/polyester composite laminate under impact shock. Based on a thermodynamic approach, the objective is the evaluation of specific interlaminar delamination energy in a multi-layer composite material under impact loading causing damage to it by cracking. For modeling impact loading, it is used an experimental device based on the principle of Charpy test which is to measure residual energy of a mass movement following a shock at speeds generally between 1 and 4 m/s, on a test piece cut of standardized dimensions requested in bending. Some of available energy is consumed by the rupture of the test piece. The results of this work showed that for impact test, mode I fracture energy is function of impact speed and the load fall energy. These results could be useful in the design of multilayer structures in composite materials subjected to impact loads.
Nano composite materials based on polymers are widely used in restoration martials like dental. Poly methyl methacrylate (PMMA) is one of the most used polymers as dental material. PMMA has disadvantages such as low flexural strength properties and impact strength. In this paper, the influences of additive aluminum oxide and hydroxyapatite nanoparticles on the mechanical and strength properties of PMMA (including flexural strength, impact strength, surface hardness and shrinkage behavior) is studied experimentally. For this purpose, nine standard mechanical testing samples of pure PMMA, PMMA/5HA and PMMA/10HA with various amounts of Nano aluminum oxide (3,6,8 wt.%) were prepared. The results showed that the mechanical properties of hybrid Nano-composites were significantly improved in comparison with the pure samples in a way that optimal Nano-composite with convenience flexural properties and impact strength is obtained. Moreover, the use of nanoparticles results in shrinkage reduction of hybrid Nano-composites in comparison with pure PMMA.
In this paper, the effects of specimen size and crack length on the fracture toughness of polycrystalline graphite are studied. The experimental results reported in the previous studies showed that the fracture toughness of graphite increase in bigger specimen. It has been also demonstrated that the fracture toughness of graphite is nearly identical in specimens with crack length ratio less than 0.7 but decreases for grater crack length ratios. To justify the size and crack length dependency of fracture toughness, the modified form of maximum tangential stress (MMTS) criterion, which makes the use of higher order terms in calculating the stress field around the crack tip is employed. It is shown that the MMTS criterion can provide good estimates for the fracture toughness of graphite obtained from specimen with different sizes. It is also indicated that the MMTS criterion can predict very good the reported experimental fracture toughness data for samples with the crack length ratios less than 0.7.
Beams are the constituent elements of several machine parts and sophisticated structures. In this paper, efforts are made to develop suitable methods that can serve as the basis to detect crack location and to crack size from measured axial vibration data. This method is used to address the inverse problem of assessing the crack location and crack size in various beam structure. The method is based on measurement of axial natural frequencies, which are global parameter and can be easily measured from any point on the structure. In theoretical analysis, the relationship between the natural frequencies, crack location, and crack size has been developed. For identification of crack location and crack size, it was shown that data on the variation of the first two natural frequencies is sufficient. The experimental analysis is done to verify the practical applicability of the theoretical method developed.
Lightweight concrete is a suitable constructional material, which can decrease the weight of buildings and the hazards of earthquake loads. Hence, a large number of research studies have been focused on designing and manufacturing high strength lightweight concretes. In this research using the natural and industrial lightweight aggregates frequently found in the south-east region of Iran (Kerman province), high strength and low cost light weight concretes were manufactured. The effects of aggregate type, aggregate size, and concrete mixture were studied experimentally on the compressive strength of concretes and the density and cost of manufactured samples.