elyas haddadi

Examining the mechanical properties of polymer materials has particular importance due to the increasing usage of these materials. In this paper, the crack development process was identified using the experimental data obtained from the tensile tests of polyvinyl chloride polymer (PVC) to reduce the experimental test number. Some pre-cracks were created on the experimental samples by slotting and broaching methods and the experimental results of force versus displacement were recorded for each sample. In the next step, some mathematical pre-processing operations including equating the sampling intervals using interpolation and integration using trapezoidal methods were performed on the experimental data. In the third stage, by using the pre-processed data and the Least Squares (LS) identification method, the mathematical model of the system, the frequency domain discrete transfer function of the crack development process, was obtained. Finally, after evaluating and verifying the obtained mathematical model with other experimental results, it was proposed to predict the crack development process. The obtained results showed that by identifying the crack development process for limited samples, it is possible to avoid the number of experimental tests that are time-consuming and costly. In addition, the second-order two-stage least squares method with five unknown parameters was promisingly able to estimate crack development dynamics with acceptable accuracy, particularly in the first half of the development process.

Linear viscoelastic constitutive laws, such as hyperelasticity with the Prony series, are commonly used in commercial software to simulate polymer materials. However, these models are not accurate regarding large strain problems despite performing well for small strain problems. To gather experimental data for soft adhesives, various shear modes were employed, including monotonic, creep, and low-cycle tests using single-lap shear specimens. These tests were conducted on optically clear adhesives (OCAs). Initially, the validity range for linear viscoelasticity was established, revealing the inability to predict large strains accurately using this approach. Subsequently, the three-network viscoplastic (TNV) model parameters were calibrated experimentally under large strains. The calibration procedures took advantage of variations in loading modes, enhancing the precision and improving the accuracy of the constitutive models. For calibration purposes, it is recommended to utilize the low-cycle loading-unloading test as it offers a suitable and cost-effective means of precision. This approach provides a cost-effective way to accurately predict material behavior, owing to the variations in loading modes. Finally, the characteristic model was used to evaluate the results through the finite element method. The results showed that the proposed model accurately predicts stress values, energy dissipation, and energy loss due to softening

Skills training have been welcomed as employment training students and graduated of university students. This paper surveys ways to increase the skills of students while studying for entrepreneurship and job creation, through the design of skills training and internship in a new way. In this regard, the center of entrepreneurship and graduate students to enhance the professional competence of college students and graduates paid with the approach to meet the needs of the country's labor market for to the specialist staff of the national design workshop in a new way in cooperation with universities to provide a platform for increasing job satisfaction among alumni who will be attracted to the labor market and thereby increase entrepreneurship, productivity and profitability of the industry. With increasing student skills can increase entrepreneurship and job satisfaction. Nearly 1% of the professors and 3% of the students had a very good opinion of the old-fashioned internship, when they reached 20% and 25% in new way of internship, respectively

Pure mode II fracture toughness of polymethyl methacrylate and its components has been studied by essential work of fracture (EWF) approach via experimental and numerical methods. EWF fracture tests with double edge notched tension (DENT) were performed on the RT-PMMA specimens at room temperature. In this investigation, the mode II fracture of polymethyl methacrylate/graft-acrylonitrile butadiene styrene (PMMA/g-ABS) blends with different weight percentage of rubber (0, 10, 15, and 20) and the thickness of samples 0.8 and 4 millimeters was investigated. The results showed that the value for the specific essential work of fracture given by including lower ligament length may be more accurate, because the ligament is completely yielded. The results also showed that for the load-displacement curves have self-similarity in shapes for the specimens with different rubber content, specimen thicknesses, and ligament lengths and the specific work of fracture (wf) increases significantly with the increasing of rubber content. The non-essential work of fracture (βwp) increases with the increasing of rubber content and the highest value belong to 20% composition in which for both thickness. The highest value of the essential work and the non-essential work of fracture belong to 20% composition in 0.8 mm specimen thickness 98.67 kJ/m2 and 99 kJ/m2, respectively. By changing the thickness of the samples the amount of the essential work of fracture showed significant changes.