مجله مهندسی ساخت و تولید ایران
سال نهم شماره 1 (فروردین 1401)

Digital shearography, as a non-destructive testing method is based on laser interferometry, which detects defects by measuring the mechanical response of the specimen to the external loading. In this study, thermal loading was applied in an alternating way to the conventional shearography method in order to investigate its effect on the defects ascertainability in different sizes and depths. A total of 15 lock-in shearography tests with different modulation frequency and loading cycle were carried out on a polymer specimen with 9 planar defects in different sizes and depths and the results were compared with conventional shearography. In the conventional method, only 4 out of 9 defect areas were detected in the specimen, while by applying lock-in stimulation with a modulation frequency of 0.02 Hz, all of 9 defect areas were revealed. The results showed that increasing the number of loading cycles does not have a significant effect on the detection capacity of defects. Also, detection of deeper defects requires the implementation of lower modulation frequencies, and defects detectability is improved with decreasing modulation frequency, so that the mean phase difference increases 2.1 times by reducing the modulation frequency from 0.1 to 0.02 Hz.

In this research the effect of different rotational speeds and different chosen materials for producing the Bobbin tool in friction stir welding process on hardness and impact resistance alterations for Aluminum 6061-T6 alloy is being studied. According to the results, the most desirable tool to accomplish this process should be from H13 hot-work steel and the pin length should be as long as the work piece thickness. The most optimized ratio between tool shoulders diameter and pin length is about 3 to 5. Accordingly, the designed tool for the mentioned process had 20 mm shoulder diameter, 6 mm pin diameter and 4 mm pin length. Results showed that increasing the rotational speed had desirable effect on connections outward quality and also cause raising the amount of consumed energy for breaking the work pieces and naturally it decreases the return angle of the projectile. Microstructure hardness tests showed that welding speed increasing caused welded zone grains size changing. So it will increase the weld hardness. Furthermore, joints macrostructure’s defects studied and determined that increasing rotational speed has good effect in decreasing these defects. Also in this research, the effect of using HSS tool steel as the bobbin tool material checked that despite better results in hardness tests in same speeds in compared with H13 hot-work steel, finally H13 chose as the bobbin tool material due to the better strength in most other speeds. 1500 rpms selected as the best rotational speed in terms of affect on mechanical properties.

Terfenol-D as a magnetostrictive material is widely used in actuators because of its high force and displacement. One of the main limitations of Terfenol-D is dependency of its structural coefficients like elastic compliance and magnetostrictive coefficients to applied mechanical stress and magnetic field which makes it difficult to predict the actuator’s behavior. In the present paper, an analytical-experimental model is presented to predict the mentioned coefficients at different operating conditions. Initially, by using an experimental fabricated setup and tension test equipment, the nonlinear stress-strain behavior of the Terfenol-D actuator is studied at different conditions and by analyzing the obtained results and applying the linear magnetomechanical model, elastic compliance, magnetostrictive, magnetic permeability and magnetomaechanial coupling coefficients are calculated. Then, a model based on linear approximating relations is presented which can predict the coefficients at determined magnetic field intensity only by importing three values of stress. Calculating values of stress and strain by using the model and comparing the results to the experimental results shows acceptable precision of the model. Finally, the proposed model is applied to predict magnetomechanical behavior of Terfenol-D and being validated. Comparing the results to experimental ones shows capability of the model at predicting magnetomechanical behavior of Terfenol-D at different operational conditions, as the maximum errors of calculated strains and magnetic fluxes are 3% and 3.4%, respectively.

In this research work, the simultaneous effect of silica nanoparticles and microcapsules containing healing agent on the healing-mechanical behavior of glass fibers/epoxy self-healable composites was investigated. To do so, the silica nanoparticles with the different percentages (1, 3 and 5 wt.%) into the smart composite containing the 14 wt.% capsulated healing agent were dispersed. For destructing the smart composites, the quasi-static penetration test with the damage force of 3300 N was used. Also, for assessing the healing mechanical performances, the interlaminar shear strength test was used. As well as, the field emission scanning electron microscope (FESEM) was used for characterizing the related mechanisms, healing performance and interaction of nanoparticles into the composite structure. The obtained results from quasi-static penetration test showed that adding the silica nanoparticles caused to reduce the level of created damages into the composite under damage force, which finally resulted to improve the healing performance. The lowest created damage was seen in the sample containing 1 wt.% silica nanoparticles. Based on the obtained results, the composite containing 5 wt.% silica nanoparticles with healing efficiency of 118.2% had the maximum healing efficiency, as compared with other composites. The creation of V shape lines and agglomeration of silica nanoparticles as effective mechanisms on the shear strength of self-healable composites were characterized by FESEM.

Thermal and vibration stress relieving processes are among the common methods of reducing residual stresses that can be performed on the part after the manufacturing. The advantages of vibratory stress relief over thermal stress relief are no need for fixtures, time and cost savings, no weight and dimensional limitations and usability for all alloys. In this research, the numerical and experimental study of vibration stress relief process of a T-shaped weld has been done. In the first step, a T-joint was made using shielded metal arc welding . The longitudinal and transverse residual stresses equal to 251 MPa and 191 MPa were measured, respectively. The differences between the calculated and the measured residual stresses in the longitudinal and transverse direction are about 17% and 1.5%, respectively. Then, by finite element simulating the vibration stress relieving process, the optimal values of the parameters affecting the process, such as the frequency of force exertion, the amount of force and the location of force exertion, were obtained. The most effective vibration stress relief condition related to the case with the applied force equal to 20% of the yield force of the sample and the excitation frequency equal to 95% of the natural frequency of the sample. The differences between the calculated and the measured residual stresses after vibration stress relief process is about 10%. By increasing the applied load frequency to 95% of natural frequency of the sample, longitudinal and transverse residual stresses decreased by more than 55% and about 70%, respectively.

During the drilling of the jawbone, the temperature could increase and cause thermal injury in the bone. So, it appears necessary to investigate the temperature rise during bone drilling. Due to the difficulty of experimental study of temperature increase during the jawbone drilling, predicting the heat transferred to the bone during surgery, leads to the correct selection of factors affecting the temperature. Therefore, in this paper, for the first time, using the finite difference method and Wiener coefficients, the temperature of the jawbone during drilling was predicted and the influence of different drilling parameters on the temperature rise was evaluated. Spindle speed were 200, 400, 800, 1200 and 2500 rpm, feed rate 50, 60, 90 and 120 mm/min and drill point angle 70, 90 and 118 degrees. Results showed that an increase in spindle speed and decrease in feed rate caused an increase in bone temperature. Also, with an increase in drill point angle from 70 to 118 degrees, the temperature increases by 10 degrees Celsius. Finally, the following combination of parameter values is suggested: feed rate of 90 to 120mm/min, spindle speeds of 200 to 2500rpm and point angle of 70˚ and 90˚. With irrigation, the decrease in temperature was almost equal to 9˚C.