The work described in this Ph. D. Thesis is developed in the context of tribology research and it is aimed to represent a support to engineers and researchers to estimate the tribological conditions and properties of the mechanical components in reciprocal contact. The main target of this research is to define a predictive wear model based on a mixed approach, obtained through the union of experimental results and numerical outcomes. The wear model is defined by implementing two tribological laws, in order to evaluate the wear depth progression occurring in a contact interface. Experimental results obtained from experimental tests define the main tribological characteristics to be used during the wear model definition process, giving the possibility to obtain a matching procedure between the experimental and numerical analyses. The first part of the work defines the tribologic domain and its main characteristics. An historic review of tribology is described in Chapter 1 and its development in surfaces study is depicted. Friction coefficient and wear definition and overview are described and their main features are outlined in order to characterize as better as possible the contact process occurring between surfaces. A literature review is collected and reported in order to support the assumptions made in the first section of this work. Chapter 2 is characterized by a description of the experimental tests usually performed to obtain the tribological characteristics of materials in reciprocal contact and an initial definition of test benches used to perform the analyses. The second part of Chapter 2 is addressed to a description of several preliminary tests performed in order to evaluate the Block-on-Ring test bench characteristics and to optimize the working conditions of the test bench itself. A comparison between the preliminary tests results and the evaluations on the tribological results obtained from literature is defined in the final part of chapter, outlining a good accuracy of the test bench. The central part of this work is characterized by three different experimental analyses performed with the main aim of defining tribological properties of different materials in contact. Chapter 3 is addressed to a description of nanomaterials coatings used with the aim of obtaining a reduction of friction coefficient in the relative contact of automotive components. The experimental campaign is performed using a Block-on-Ring test bench in order to obtain tribological characteristics of nano-coatings. Following the same approach and objective, in Chapter 4 a discussion on experimental tests performed on reinforced epoxy resins is presented. The resins, reinforced with different graphene nanopowders, are applied on the external surface of the ring during a Block-on-Ring contact configuration. The evaluation of tribological characteristics during a camshaft working conditions replications, defines the possibility of an epoxy resin implementation in the internal combustion engine components. Chapter 5 illustrates a study on the molybdenum treatment usually used in clutch pack assemblies. The aim of this research concerns the evaluation of the friction coefficient and of the wear rate generated during the contact between a treated ring and an untreated block. The tribological evaluation leads to a deeper understanding of the behavior of the materials in contact, to define the design of the clutch pack composed by molybdenum-treated disks. The experimental research takes into account the evolution of tribological properties as a function of time to estimate wear progression during components lifetime. After an experimental characterization of several external treatments, a numerical approach is followed in order to define a predictive wear model based on experimental results. Chapter 6 illustrates the Block-on-Ring characterization in a finite element domain with the aim to represent the contact configuration defined in experimental tests. The target of this part of the dissertation concerns the definition of a wear model based on fundamental tribological laws and their implementation in a custom algorithm. The iterative process defined in the procedure allows the definition of wear depth increments with time, defining consequently the lifetime of components in contact. The final chapter describes an application of numerical wear model in the clutch pack of a Limited Slip Differential. The aim of this section is the evaluation of wear evolution on disks contact surfaces and the consequent performance decay highlighted in the clutch pack in terms of transmissible torque. The results are critically discussed in Conclusions sections, defining strengths and weaknesses of predictive wear model. An outlook of future applications and possible implementation of the model are described in the same section, highlighting the possibility of a prediction process during design phase of mechanical components.

Definition of a FEA based approach to predict the frictional behavior of wearing surfaces / Tesi, Amedeo. - (2017).

Definition of a FEA based approach to predict the frictional behavior of wearing surfaces

TESI, AMEDEO
2017

Abstract

The work described in this Ph. D. Thesis is developed in the context of tribology research and it is aimed to represent a support to engineers and researchers to estimate the tribological conditions and properties of the mechanical components in reciprocal contact. The main target of this research is to define a predictive wear model based on a mixed approach, obtained through the union of experimental results and numerical outcomes. The wear model is defined by implementing two tribological laws, in order to evaluate the wear depth progression occurring in a contact interface. Experimental results obtained from experimental tests define the main tribological characteristics to be used during the wear model definition process, giving the possibility to obtain a matching procedure between the experimental and numerical analyses. The first part of the work defines the tribologic domain and its main characteristics. An historic review of tribology is described in Chapter 1 and its development in surfaces study is depicted. Friction coefficient and wear definition and overview are described and their main features are outlined in order to characterize as better as possible the contact process occurring between surfaces. A literature review is collected and reported in order to support the assumptions made in the first section of this work. Chapter 2 is characterized by a description of the experimental tests usually performed to obtain the tribological characteristics of materials in reciprocal contact and an initial definition of test benches used to perform the analyses. The second part of Chapter 2 is addressed to a description of several preliminary tests performed in order to evaluate the Block-on-Ring test bench characteristics and to optimize the working conditions of the test bench itself. A comparison between the preliminary tests results and the evaluations on the tribological results obtained from literature is defined in the final part of chapter, outlining a good accuracy of the test bench. The central part of this work is characterized by three different experimental analyses performed with the main aim of defining tribological properties of different materials in contact. Chapter 3 is addressed to a description of nanomaterials coatings used with the aim of obtaining a reduction of friction coefficient in the relative contact of automotive components. The experimental campaign is performed using a Block-on-Ring test bench in order to obtain tribological characteristics of nano-coatings. Following the same approach and objective, in Chapter 4 a discussion on experimental tests performed on reinforced epoxy resins is presented. The resins, reinforced with different graphene nanopowders, are applied on the external surface of the ring during a Block-on-Ring contact configuration. The evaluation of tribological characteristics during a camshaft working conditions replications, defines the possibility of an epoxy resin implementation in the internal combustion engine components. Chapter 5 illustrates a study on the molybdenum treatment usually used in clutch pack assemblies. The aim of this research concerns the evaluation of the friction coefficient and of the wear rate generated during the contact between a treated ring and an untreated block. The tribological evaluation leads to a deeper understanding of the behavior of the materials in contact, to define the design of the clutch pack composed by molybdenum-treated disks. The experimental research takes into account the evolution of tribological properties as a function of time to estimate wear progression during components lifetime. After an experimental characterization of several external treatments, a numerical approach is followed in order to define a predictive wear model based on experimental results. Chapter 6 illustrates the Block-on-Ring characterization in a finite element domain with the aim to represent the contact configuration defined in experimental tests. The target of this part of the dissertation concerns the definition of a wear model based on fundamental tribological laws and their implementation in a custom algorithm. The iterative process defined in the procedure allows the definition of wear depth increments with time, defining consequently the lifetime of components in contact. The final chapter describes an application of numerical wear model in the clutch pack of a Limited Slip Differential. The aim of this section is the evaluation of wear evolution on disks contact surfaces and the consequent performance decay highlighted in the clutch pack in terms of transmissible torque. The results are critically discussed in Conclusions sections, defining strengths and weaknesses of predictive wear model. An outlook of future applications and possible implementation of the model are described in the same section, highlighting the possibility of a prediction process during design phase of mechanical components.
2017
Renzo Capitani, Claudio Annicchiarico
ITALIA
Tesi, Amedeo
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/1084910
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