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CNAA / Theses / 2022 / /

Improving the methods used to calculate engineering fits of tribological couples renovated with heterogeneous materials

Author: Șeremet Dumitru
Degree:doctor of engineering
Speciality: 05.20.03 - Exploitation and Maintenance of Agricultural Machinery and Food Industry
Scientific adviser: Grigore Marian
doctor habilitat, professor, Agrarian State University of Moldova
Institution: Agrarian State University of Moldova


The thesis was presented on the 29 September, 2022
Approved by NCAA on the 21 December, 2022


Adobe PDF document1.48 Mb / in romanian


CZU 631.3+539.3

Adobe PDF document 4.94 Mb / in romanian
143 pages


Engineering fit, Tolerance class, Dimensional accuracy, Green’s functions, Interference fits, Clearance fits


The thesis consists of the introduction, four chapters, conclusions and recommendations, bibliography of 127 sources, 2 Annexes, 124 pages (up to bibliography), 28 figures, 3 tables. The obtained results are published in 15 scientific papers, including 4 ISI resources.

Field of study: Engineering sciences and technologies. Calculation of engineering fits of renovated tribological couples. Aim of the paper: Improving the quality of repaired agricultural equipment by applying an improved method of calculating adjustments of renovated tribological couples with heterogeneous materials by applying Green functions.

Research objectives: To develop, promote and apply theoretical bases related to the calculation of geometric accuracy for machine parts reconditioned by compensating their wear with the application of material layers, characterized by special properties and improvement of the methods used to calculate joint fits that consist of reconditioned heterogeneous materials, to develop an algorithm used to calculate fits employing the improved method.

Scientific novelty includes:
- a transdisciplinary approach for the issues related to the accuracy when designing joint fits made of parts reconditioned utilizing different materials through achievements in the fields of interchangeability, solid body mechanics and with the trends specific to reliability and availability of agricultural machinery subject to maintenance interventions;
- detailed critical analysis of the actual state regarding the methods of calculating joint fits renovated with heterogeneous materials and the ways to improve them;
- improvement of theoretical bases of existing methods used to calculate the geometric accuracy of reconditioned machine parts and fits in these parts by developing algorithms to solve mono- and multi-dimensional boundary problems with their subsequent use when determining the value of fits of clearance and interference joints.

The obtained results that contribute to solving important scientific problems are expressed by acquiring new knowledge, capitalized by developing an original method of calculating joint fits made of reconditioned parts that differ from existing ones by solving boundary problems in the contact area with the application of Green’s functions, which led to the improved design, technological and functional accuracy.

Theoretical significance refers to the quality improvement of the agricultural equipment repaired by improving the method of calculating the fits of different joints renovated with heterogeneous materials.

Applicative value of the paper consists in the possibility to use the proposed calculation method to increase the calculation accuracy of joint fits of renovated machine parts and to improve the training process of Bachelor’s, Master’s and Doctoral students in science and engineering.