International Journal of Mechanical and Materials Engineering

Trình bày các kết quả thí nghiệm về tác động của nồng độ, thời gian lão hóa và thời gian ủ nhiệt đến các tính chất quang học và cấu trúc của màng mỏng oxit kẽm (ZnO) và oxit kẽm pha tạp nhôm (ZnO:Al) chế tạo từ sol gel. Các màng mỏng ZnO và ZnO:Al được chế tạo trên các nền kính bằng phương pháp spin coating, sau đó được ủ nhiệt. Phân tích XRD xác nhận rằng các màng này là đa tinh thể dạng wurtzite. Đối với các màng có nồng độ thấp (0,2 và 0,4 M), kích thước hạt tăng lên theo thời gian lão hóa lên đến 72 giờ. Đối với các mẫu có nồng độ cao (0,6 và 0,8 M), kích thước hạt chỉ tăng đến 48 giờ. Thời gian lão hóa thêm dẫn đến sự giảm kích thước hạt. Kích thước hạt lớn nhất được tìm thấy cho 0,4 M sau 72 giờ và 0,6 M sau 48 giờ. Hệ số năng lượng băng (band gap) có xu hướng giảm khi thời gian lão hóa tăng lên cho tất cả các nồng độ. Hệ số năng lượng băng nhỏ nhất cho mỗi thời gian lão hóa (24, 48 và 72 giờ) được quan sát đối với các màng 0,6 M. Những kết quả này cho thấy rằng nồng độ sol gel cao gần 0,6 M có thể mang lại các tính chất tốt hơn với thời gian lão hóa ngắn hơn so với các màng 0,2 và 0,4 M. Dữ liệu từ quá trình ủ nhiệt cho thấy 350 oC là nhiệt độ ủ tối thiểu trong 1 giờ để đạt được các màng chất lượng cao và các màng ZnO có nồng độ cao có các đỉnh nhiễu xạ mạnh hơn. ZnO:Al cũng thể hiện các đỉnh nhiễu xạ mạnh hơn và sự dịch chuyển về phía xanh lớn hơn của băng với việc tăng nồng độ sol gel.

Composite material is being used in vehicles for protective structures against blast loading. Limited data is available which compare experimental works and numerical analysis in the open field environment. More data is needed in this area in order to be able to predict and use composite materials safely. In this work, the response of woven glass/epoxy composite plates under blast loading was investigated, both experimentally and numerically. The plate was manufactured using glass/epoxy woven Cytec 120 °C curing system. The explosive material was Tri-Nitro-Toluen (TNT) with different masses, which are 60, 80, and 100 g. The stand-off distance was also varied, ranging from 300 up to 1000 mm. In the experimental work, a sewing needle pin was put under the plate to record the maximum deformation of the plate during TNT explosion. In the numerical analysis, LS-DYNA was used extensively. The composite plate was modeled as shell elements using MAT54, and the failure criteria was Chang-Chang failure criteria. The explosive TNT material was modeled in two different ways. First, it was modeled using CONWEP and the second was modeled using Smooth Particle Hydrodynamics (SPH). The numerical analysis results were then compared with the experimental data for the case of maximum deformation. Experimentally, the sewing needle method was able to measure the plate maximum deformation during the explosion. The numerical analysis showed that the SPH model gave better agreement with experimental results compared with CONWEP method. The SPH results were in the range of 8–18% compared to experimental data, while the CONWEP results were in the range of 14–43%. Albeit its simplicity, sewing needle method was able to measure the maximum deformation for blast loading experimentation. The SPH model was better compared with CONWEP method in analyzing the response of composite plate subjected to blast loading.

An ISO standard tooth profile has a symmetric pressure angle of 20°. However, the load capacity can be increased with respect to bending and contact pressure by increasing the pressure angle on the meshing side of an asymmetric tooth. Accordingly, we analyzed the torque transmission capacity of asymmetric gears with various pressure angles. We calculated the deflection and bending stress of teeth by the finite element method and found the root stress taking into account the load-sharing ratio. Hertzian contact stress was calculated with respect to contact pressure. Normal vector load was converted into a torque, and torque capacity was evaluated when the stress reached the allowable stress for each case. Reduced bending stress because of an increase in tooth thickness and decreased transmission torque because of a reduction in the base circle radius work together to maximize the load capacity for bending at a pressure angle of around 30°. Maximum load capacity with respect to contact pressure is achieved when the pressure angle is made 45° by increasing the radius of the contact surface. Both strength with respect to bending and contact pressure are found, and the torque transmission capacity of the gear is determined by the lower value of the two. For low-strength materials such as flame-hardened steel, damage due to contact pressure is expected for all forms of gears and the greatest torque capacity was at a pressure angle of 45°. In the case of assuming 800 Hv and an inclusion size $$ \sqrt{\boldsymbol{A}}=50 $$  μm for a high-strength material, the greatest torque transmission capacity is obtained at a pressure angle of 30°. In the case of assuming a moderate-strength material such as case-hardened steel, an optimal form exists at which strength with respect to bending and strength with respect to contact pressure are equal.

The challenge encountered in continuous forming process is the variation in mechanical strength of product formed with respect to process variables like extrusion wheel speed and diameter of product. In this research article, the micro-structural investigation of the aluminum (AA1100) feedstock material of 9.5-mm diameter has been carried out at various extrusion wheel speeds and diameter of product before and after deformation on commercial continuous extrusion setup TBJ350. The mechanical properties like yield strength as well as percentage elongation have been estimated and optimized using two variables with 3 levels through central composite rotatable design (CCRD) method. The mathematical modeling has been carried out to predict the optimum combination of process parameters for obtaining maximum value of yield strength and percentage elongation. The statistical significance of mathematical model is verified through analysis of variance (ANOVA). The optimum value of yield strength is found to be 70.939 MPa at wheel velocity of 8.63 rpm and product diameter of 9 mm respectively, whereas the maximum percentage elongation recorded is 46.457 at wheel velocity of 7.06 rpm and product diameter of 7.18 mm. The outcome may be useful in obtaining the best parametric combination of wheel speed and extrusion ratio for best strength of the product.

Metal forming has played a significant role in manufacturing development, thus investigations in the field of metal forming to improve the quality of the forming process are necessary. In the present study, the experimental and numerical analysis of airfoil contour forming of 301 austenitic stainless steel is examined in order to reduce the spring reversible ability under preheat temperature. Considering the stress-strain properties of the preheat temperature; the body forming is simulated in ABAQUS software according to the theory of increasing the blank holder force during forming. The obtained results of the spring-back for simulating the austenitic stainless steel airfoil are compared and investigated with the manufactured experimental sample results using deep tensile forming. By comparing the results it can be seen that the control of blank holder force during forming cause to minimize the spring-back effects.

The constitutive behavior and failure of ductile materials are described in the present work for a general case of loading in terms of the secant moduli, which depend on the first (dilatational) and second (deviatoric) strain invariants. This approach exposes the distinct behavior of materials to the equivalent normal and shear stresses. The secant moduli enable the establishment of two (instead of one) constitutive equations necessary for the complete description of these materials. Emphasis is given in the accuracy of the resulting constitutive equations in terms of their predictions relative to actual experimental data for two materials systems. Failure predictions, according to T-criterion, are derived for two materials under combined torsion and tension, which are in good agreement with experimental data. Finally, the associated failure surfaces in a stress space are presented as well.

Laser micromachining is currently used in the MEMS production to replace the traditional etching process which consumes longer time to complete. The objective of this study is to investigate the drilling capability of industrial CO2 laser in processing of silicon wafer. In this work, the holes were drilled on P-type silicon wafer with thickness of 525 μm. Geometrical characteristic of holes produce, which is diameter entrance that depends on laser parameter were investigated and analyzed. Analysis of Variance (ANOVA) was used to analyze the result and generated an appropriate model for the laser drilling processing. The laser parameters involved were laser power, pulse frequency and duty cycle. The experimental results showed the entrance diameter of drilling holes was increase when the laser power and duty cycle increased. The entrance diameter of drilling hole decreases when the pulse frequency increases.

Heat exchanger is a device in many industrial applications and energy conversion systems. Various heat exchangers are designed for different industrial processes and applications. Shell and tube heat exchanger (STHE) has its own importance in the process industries. Experimental and numerical simulations are carried for a single shell and multiple pass heat exchangers with different tube geometries i.e. circular tubes to elliptical tubes. The experiment was carried out with hot fluid in tube side and cold fluid in shell side with circular tubes at 600 tube orientation and 25 % baffle cut. Heat transfer rates and pressure drops are calculated for various Reynolds numbers from 4000 to 20000. Fluent software is used for numerical investigations. Both circular and elliptical tube geometries with 450,600 and 900 orientations are used for the numerical studies. In addition to 25 % baffle cut, quarter baffle cut and mirror quarter baffle cut arrangements are used for comparison. The experimental values of heat transfer rates and pressure drops over shell side and tube side along the length of STHE are compared with those obtained from fluent software. It is found that the elliptical tube geometry with mirror quarter baffle cut at 450 tube orientation is 10 % higher than existing shell and tube heat exchanger and the pressure drop decrement in tube side shows up to 25 %.