The effect of the type of reinforcement was studied using Charpy impact test as well as hardness test. The material used is composed of polyester reinforced with fiber glass; a material increasingly and widely used in plenty of engineering applications, recently. In order to maximize the output of the present work, studies were carried out on different weight fraction of reinforcement. Two types of composite reinforcement were tested, namely the use of chopped fibers (randomly distributed glass fibers) and woven roving (laying fibers normal to the randomly distributed ones). It has been noted that the values of the Charpy impact resistance and hardness of the tested specimens, yield increases for weight fractions of reinforcement of about 30% to 40%. The results show that there is a scatter in the values of Charpy impact resistance and hardness in the ranges of weight fraction below and higher than the 30% to 40% range. It is also observed that the values of Charpy impact resistance and hardness of the chopped composites are higher than those of chopped and woven roven ones due to the fiber distribution and orientation. The direction of the load is at random angles of orientation to the Chopped fibers in the case of Chopped fibers. The paper discusses the results to explain the out coming trends.
Detecting defects in various industrial products remains a challenging task in the industry. Researchers are constantly working to improve detection techniques and tools for various defects, particularly cracks. Many industrial structures suffer from cracks. The selection of a suitable technique and/or tool is based upon the tested structures and the accuracy of the technique and/or tool. The work's novelty is the development of a fully accurate, simple, and safe ultrasonic tool for precisely scanning cracks. A pen-shaped cone was added to the ultrasonic transducers to improve their performance. Different crosshead speeds and annealing techniques were used to cause cracks on medium density polyethylene (MDPE) and poly-methyl-methacrylate (PMMA) polymer plates with specific dimensions. Cone reduced the front diameter of the transducers from 12 to 2 mm (cone tip diameter). It improved the transducers by giving them new properties such as a small near field, a collimated beam, high sensitivity, and high wave reflection. The modified transducers tracked the cracks at discrete sequential sites, where the ultrasonic velocity was measured to determine the crack speed, critical crack speed, dynamic stress intensity factor, and crack branching phenomenon. Additionally, ultrasonic attenuation was measured in order to accurately determine crack growth behavior, the crack's neck zone, and the crack growth dependency on both plate thickness and annealing. Scanning electron microscope (SEM) images revealed crack propagation in polymer plates. The results of ultrasonic testing and SEM evaluations were consistent. This guaranteed that the modified transducers could scan cracks accurately.
The indicated value on the displaying device of a digital measuring instrument is usually considered as the resultant of rounding the measurand value to the nearest indication. This hypothesis is conventional and forms the basis of estimating the resolution uncertainty associated with digital indications. However, the essential quantization process needed in converting the measurand analog signal into a digital form makes the precise estimation of the resolution uncertainty shift from the one based on the aforementioned hypothesis. In this study, the effect of the quantization process on the resolution uncertainty was analyzed, a proposed algorithm for the estimation process was presented, and finally the impact of noise presence was considered. Based on the current study, the measurement result usually has a shift from the indicated value. In the presence of noise, the resolution uncertainty of stable indications can be reduced if the peak-to-peak noise could be quantified with adequate accuracy.Also, the current study recommends the revision of the broad applicability of the conventional estimation method of the resolution uncertainty and encourages standardization bodies to specify the main requirements in digital measuring instruments that guarantee their indicating behavior.
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