Papers by Author: Alexandru Paraschiv

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Authors: Gheorghe Matache, Valeriu Dragan, Cristian Puscasu, Valeriu Vilag, Alexandru Paraschiv
Abstract: The paper presents a comparison between Coordinate Measuring Machine and 3D white light scanning technologies as applied to the dimensional inspection of turbo-machinery parts such as turbine blade. The results were compared with the CAD model and each other. The results indicate that, even both methods are enough accurate with a slightly better accuracy for CMM, the operational speed and the variety of scanable surfaces give significant advantages to the 3D scanning method when prototypes require dimensional inspection by an alternative rapid route especially when dealing with objects with thin walls or sharp edges.
Authors: Gheorghe Matache, Alexandru Paraschiv, Cristian Puscasu
Abstract: The wear behaviour of thick molybdenum coatings deposited by electric arc thermal spray on steel support was investigated by micro-abrasion, a relatively recent introduced method for small scale wear testing. The wear mechanisms and wear rates without coatings penetration were investigated with respect of time corresponding to primary and secondary wear stages. The micro-abrasion of Mo coatings using SiC abrasive slurry have been discussed and wear scar characteristics were evaluated based on the experimentally results. The worn surfaces of the tested specimen were examined by SEM and the specific wear rate was calculated from experimental data. For the testing durations used it was identified the change from grooving to rolling wear corresponding to the transition of wear mode from two-body to three body-abrasion.
Authors: Mihaela Raluca Condruz, Alexandru Paraschiv, Ionuț Sebastian Vintilă, Mihail Sima, Andreea Deutschlander, Florin Dumitru
Abstract: The analysis of damage resulted from concentrated out-of-plane impact forces is a concern in case of fiber reinforced polymeric composite aerostructures. Thereby, it can be quantified in terms of resulting size/damage type by drop weight impact testing. The aim of the present research was to evaluate the impact response of CFRP laminates by FEA and experimental tests. For FEA, two failure criterions were used, energetic criterion and Tsai Wu criterion. In both modeling scenarios the laminate was fractured. In case of the energetic criterion it was observed a meandering crack along with internal delamination of the material plies, while in case of the Tsai Wu criterion the impactor passes through the specimen, destroying the impacted area. Experimental tests performed at 0.7 meters height and 33 J of impact energy showed that all material plies were visible damaged, but the impactor didn’t pass through all specimen thickness. Different damage modes were observed on the tested specimens, the impacted face of the specimen presented a combined damage consisting in large cracks with fiber breakage indentation/puncture and a dent while on the non-impacted side of the specimen splits, cracks and a small swelling were observed. Considering the results from FEA and experimental tests, it can be said that regarding the damage shape, the experimental results are in a good agreement with a combination of the results obtained from the two failure models of FEA.
Authors: Gheorghe Matache, Cristian Puscasu, Alexandru Paraschiv, Oana Trusca
Abstract: Thermal sprayed Mo coatings deposited on steel support deposited by electric arc and atmospheric plasma spray were investigated. Microstructural investigation of the coatings showed that in both variants the splats formed by rapid solidification and splashing during the impact with the substrate have irregular shape, exhibit cracks and scattered debris. The measured average equivalent diameter of the splats and the calculated average diameter of the particles that generated the splats are higher for electric arc spraying. Using the measured and calculated data it was descibed the relathionship between splats diameter, splats thickness and flattening degree. Some intrinsec properties of the coatings as roughness, hardness and bond strength were measured. All these properties are influenced by the splat size. Lower size of the splats lead to reduced surface roughness, higher hardness and higher bond strength of the coatings.
Authors: Alexandru Paraschiv, Gheorghe Matache, Cristian Puscasu, Mihaela Raluca Condruz
Abstract: The effects of micro-abrasion wear on the surface roughness of molybdenum coatings deposited by electric arc thermal spray on steel support were investigated. The 2D surface roughness was measured and correlated with the experimental results of the micro-abrasion tests. Different worn surfaces which correspond to running-in and steady stage of wear were investigated in terms of the microstructure, 3D image and 2D surface roughness. The micro-abrasion tests were made in the presence of a SiC abrasive slurry for test durations between 200 – 1600 s and the worn surfaces were evaluated by scanning electron microscopy and stereomicroscopy.
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