نشریه مهندسی مکانیک مدرس
سال بیست و یکم شماره 4 (فروردین 1400)

In the present study, the wake flow field of a submarine model was investigated experimentally in a wind tunnel. The experiments were conducted to determine the effect of the location of control surfaces on the wake inflow to the impeller of the submarine. In order to investigate the effect of the location of control surfaces as the most important innovation of the present study, the aforementioned surfaces were installed in three longitudinal positions X/L=0.89, 0.92, 0.95 on the heel of the submarine model, and the wake flow was measured at position X/L=1.7 and the Reynolds number 6*10^5  by a five-hole probe and a hotwire anemometer. Finally, the longitudinal position X/L=0.95 was selected as the optimal location for the stern planes to improve the wake inflow to the impeller in terms of reducing its total area and the least amount of turbulence and non-uniformity. The results obtained during this study showed that arriving of the holder basechr(chr('39')39chr('39'))s wake to the stern area increases ​​the area and average velocity and subsequently reducing the non-uniformity of the wake flow.

Delamination is one of the most common modes of damage in laminated composites that can reduce stiffness and load-bearing capacity of the composite structure, which highlights the importance of studying of this phenomenon. For this purpose, in this study, the effect of the interface fiber angles on the mode II fracture toughness of plain woven laminated composites has been investigated. The end notch flexure specimens (ENF) with 24 layers which have 0//0, 0//30 and 30//-30 interface angles manufactured using hand lay-up method and experimental tests conducted on them in accordance with ASTM standard under load II mode loading. Experimental results show that the interface fiber angle has a significant effect on initiation and propagation of delamination toughness the initial and propagation fracture toughness, so that the load bearing capacity of the specimens with the non-zero interface fiber angle was the highest value. Moreover, the initiation and propagation value of fracture toughness for specimens with 0//0 interface fiber angle was less than the corresponding values for other samples with non-zero interface angles. In addition, the fracture process zone (FPZ) length was approximately the same for all samples. Taken images of fracture surfaces using scanning electron microscopy (SEM) show that in addition to the separation of fibers from the resin at delamination, other damage mechanisms Including fiber breakage and highly deformed matrix play a key role in increasing of the fracture toughness of the sample with 0//30 and 30//-30 interface fiber angle.

In this research, the abrasion resistance of components made by Additive Manufacturing (AM) has been modeled. AM is widely used in various industries today and the Fused Deposition Modelling (FDM) process is one of the most popular methods of fabrication in this field. Although many researches have been done with the aim of modeling mechanical behavior in this field, but limited studies have been done in the field of wear and modeling of this phenomenon. In this research, in order to create an exact mathematical relationship between the input variables (layer thickness, raster angle and air gap) and the response variable (wear rate), the experimental design using the Central Composite Design (CCD) method has been done. Twenty systematic experiments were performed to determine the response and provide a proportional regression model. Using analyze of variance (ANOVA), a mathematical model corresponding to the actual process was obtained, and the validity of the proposed model was confirmed by statistical methods. The result show that the proposed model predicts the wear rate of Acrylonitrile Butadiene Styrene (ABS) parts made by FDM method with a coefficient of determination of 95.62%. The result of the experimental study and model analysis showed that the variable of air gap and the effect of its interaction with raster angle, creates the highest wear rate and also the second-order effect of layer thickness has the most negative effect on wear rate.

Forming Limit Diagrams (FLDs) are very useful measures for safe forming of sheet metals without failure due to necking or fracture under different loading conditions. This paper uses ductile fracture criteria to predict the formability of low carbon steel sheets to evaluate their accuracy in predicting the FLDs. In addition, the fracture forming limit curves (FFLD) and necking forming limit curves (NFLD) for St12 low-carbon steel have been extracted experimentally and numerically. In the experimental procedure, the Nakazima stretching test was used. In the numerical procedure, by defining six phenomenological ductile fracture criteria in ABAQUS / Explicit finite element software, the failure is predicted and compared with the experimental results. These criteria were calibrated using 6 tests namely as In-plane shear, uniaxial tensile test, circle hole test, notched tension test, plane stress test, and Nakazima stretching test. The results showed that the criteria, which include both the stress triaxiality (η) and Lode parameter (L), provide a more accurate prediction of failure. Also to predict necking during numerical simulation of Nakazima test and also to extract the NFLD, three criteria of the second derivative of major strain, the second derivative of thickness strain and the second derivative of equivalent plastic strain have been used.

The sandwich panel is a combination of a soft core and two stiff, high-strength facesheets. In many cases, the connection between the facesheet and the core is considered as a critical point that can damages the integrity of the sandwich structure. In this study, the debonding toughness between the facesheet and the core in sandwich beams with grooved cores made of Kevlar 49/polyester facesheets and polyurethane foam core has been measured experimentally. The values ​​of the strain energy release rate obtained at the onset of crack growth for the tested specimens are in the range of 340 (J/Square meters) and increase with the crack growth up to 500 (J/Square meters). One of the innovations of the present study is to investigate the effect of grooving the core of the sandwich panel on the resistance of the structure to the growth of interfacial cracks. The results show that by placing the groove inside the core of the sandwich panel, the interfacial crack stops during growth by hitting each groove and requires higher force to restart its growth. This phenomenon increases the resistance of this type of structure against the growth of cracks in the face/core area. In this research, a model based on cohesive zone theory was used to simulate crack growth in the tested specimens. Comparison of load-displacement curves obtained from the analysis shows that the proposed model has a good ability to predict the behavior of the structure under similar loading conditions.

Hands are complex moveable organs of the human body. some reasons such as stroke can cause the hands disordering. These patients have problem doing their daily routines. Communication between human and robots lead to inventing devices to improving ability. This paper aims to design and prototype a portable wearable robot. This robot has been designed to facilitate the daily routines of patients who are not able to extend their hands. Researchers are facing challenges like high cost due to numerous actuators and innumerous sensors used to control the system. As the number of elements used to build the device increase, the ultimate weight of the device, also, grows, and practically it loses portability. According to the importance of portability of the robot and the need for long-term use by the user, device components with less weight are designed in this work. In this regard, in the introduced mechanism, a torque is applied to the lowest metacarpophalangeal joints simultaneously by only one electric operator; therefore, fingers are opened. The power transmission system is inspired from the hand tendon with the help of the cable length changes. Because of disturbances and nonlinearity of the system, sliding mode controller to minimize the error is designed. The results demonstrate that the joint angle converges to the desired angle, and the error tends to zero. Good results of the practical test, in addition to being low cost, and weight imply that we can trust the extensibility of this project.