In the current study, the additive manufacturing of nylon by fused deposition modeling is conducted based on statistical analysis. Besides, the aim of this study is the influence of process parameters, namely layer thickness (0.15 mm-0.35 mm), infill percentage (15-55%), and the number of contours (2-6) on the maximum failure load, parts weight, elongation at break, and build time. The experiment approach was used to optimize process parameters based on the statistical evaluates to reach the best objective function. The minimum value of build time and maximize of the failure load were considered as objective functions. The response surface method is regarded as an optimization process parameter, and optimum conditions were studied by experimental research to evaluate efficiency. Based on the results, the layer thickness is the significant primary variable for all responses. The experimental evaluation showed that the maximum values of failure load and elongation were obtained by changing the layer thickness from the lowest to the highest. By reduction in layer thickness at the same printing speed, the cooling rate increases, which results in greater strength and less elongation. As a result, it could be concluded that by increasing the number of contour layers from 2 to 6, the maximum failure force increased 42%. Increasing the contours due to the similar effect to increasing the infill density, increases the failure force and production time, which is also confirmed by the ANOVA.
Tuned mass dampers (TMDs) and active tuned mass dampers (ATMDs) are control devices added in tall buildings to suppress the response of buildings in irregular external excitations such as earthquakes and wind. The performance of both passive and active damper systems can be assessed by parametric studies. This paper presents a brief description of the theory of passive and active tuned mass dampers. In this work, the effect of TMDs has been studied by changing the frequency ratio of the damper to the first mode of the structure. It was observed that the extra damping provided by TMDs, called effective damping, can primarily be obtained from design charts developed for this purpose. A 25-storey building is designed and analysed using these charts as an example. The behaviour of a structure with an active tuned mass damper is investigated. The related parameters and equations of the active mass damper for the building are solved and its behaviour arising from external loads is studied. The conventional studies, which are based on white-noise excitations, usually overestimate the performance of TMDs and ATMDs. Hence, in order to study the behaviour of a building with a TMD and an ATMD in real excitations, El-Centro and Tabas earthquakes are selected. The results show a significant increase in the effect of TMD performance in controlling the structural displacements by using additional control devices.
The attempts of researchers in industries to obtain accurate and high quality surfaces led to the invention of new methods of finishing. Magnetic abrasive finishing (MAF) is a relatively new type of finishing in which the magnetic field is used to control the abrasive tools. Applications such as the surface of molds are ones of the parts which require very high surface smoothness. Usually this type of parts has freeform surface. In this study, the effect of magnetic abrasive process parameters on freeform surfaces of parts made of aluminum is examined. This method is obtained through combination of magnetic abrasive process and Control Numerical Computer (CNC). The use of simple hemisphere for installation on the flat area of the magnets as well as magnets’ spark in curve form is a measure done during testing the experiments. The design of experiments is based on response surface methodology. The gap, the rotational speed of the spindle, and the feed rate are found influential and regression equations governing the process are also determined. The impact of intensity of the magnetic field is obtained using the finite element software of Maxwell. Results show that in concave areas of the surface, generally speaking, the surface roughness decreases to 0.2 μm from its initial 1.3 μm roughness. However, in some points the lowest surface roughness of 0.08 μm was measured.
In this paper, the energy absorption parameters are investigated for new forms of thin-walled energy absorbers. The effect of adding stiffeners to the outer tube wall, as well as the multi-cell effect of the structure, was investigated both in a separate and simultaneous manner in a tube with the square section. This design has not been investigated in previous studies, and it stimulates innovation in its own right. Such designs can significantly increase the energy absorption of the structure with the least change in the initial geometry and the lowest costs. The nonlinear explicit finite element method was used to simulate the crushing process in the tubes. The numerical simulation results were validated with the results of experimental tests, and a good agreement was observed. Finally, the parameters such as specific energy absorption, crush force efficiency, initial peak force, and mean crush force were calculated and analyzed. The results showed that the proper combination of stiffeners in the middle sides of the tube wall and the creation of a multi-cell column made it possible to improve the specific energy absorption up to 89% and crush force efficiency up to 52% compared with the reference tube, which is a significant improvement. Also, while comparing some of the results, it was analyzed why sometimes inserting stiffeners on the outer wall of tubes is better than the multi-cell method to increase the SEA of structure.
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