PROCJENA HRAPAVOSTI POVRŠINE PRIRODNIH STIJENSKIH PUKOTINA TEMELJENA NA TEHNICI NENADZIRANOG PREPOZNAVANJA UZORAKA POMOĆU 2D PROFILA

The stability of a jointed rock mass is generally controlled by its shear strength that significantly depends on surface roughness. So far, different methods have been presented for determining surface roughness using 2D profiles. In this study, a new method based on the unsupervised pattern recognition technique using a combination of statistical, geostatistical, directional, and spectral methods for the quantification of the surface roughness will be proposed. To reach this goal, more than 10,000 profiles gathered from 92 surfaces of natural rock joints were scanned. The samples were collected from limestone cores of the Lar Dam located in the Mazandaran Province, Iran. After introducing a new spectral index, determined from the fast Fourier transform for measuring the unevenness of rough profiles, statistical, geostatistical, directional, and spectral features revealing waviness and unevenness of the 2D profiles were extracted, and a representative vector and profile for each surface were introduced through the weighted mean and median of the profile features. Principal component analysis (PCA) was utilized for finding the direction of the maximum variance of information. Then, clustering of the 92 samples was performed via K-means, and the silhouette measure was used in order to find the optimal number of clusters resulted in the creation of 13 clusters. To verify the procedure, a sample was selected in each cluster, and direct shear tests were performed on the samples. Comparing the experiments and the clustering results shows they are in good agreement. Thus, the method is an efficient tool for the quantitative recognition of surface roughness considering the waviness and unevenness of a surface.Stabilnost raspucane stijenske mase općenito se kontrolira posmičnom čvrstoćom koja značajno ovisi o hrapavosti površine. Do sada su prikazane različite metode za određivanje hrapavosti površine pomoću 2D profila. U ovom radu predlaže se nova metoda koja se temelji na tehnici nenadziranog prepoznavanja uzoraka kombinacijom statističkih, geostatističkih, usmjerenih i spektralnih metoda za kvantifikaciju hrapavosti površine. Kako bi se postigao taj cilj, skenirano je više od 10.000 profila prikupljenih s 92 površine prirodnih stijenskih pukotina. Uzorci su prikupljeni iz vapnenačkih jezgri brane Lar koja se nalazi u pokrajini Mazandaran u Iranu. Nakon uvođenja novog spektralnog indeksa, određenog Fourierovom transformacijom za mjerenje neravnina hrapavih profila, izvučene su statističke, geostatističke, usmjerene i spektralne značajke koje opisuju valovitost i neravnine 2D profila, a reprezentativni vektor i profil za svaku površinu uvedeni su kroz ponderiranu aritmetičku sredinu i medijan značajki profila. Analiza glavnih komponenti (PCA) korištena je za pronalaženje smjera najvećeg odstupanja informacija. Zatim je grupiranje 92 uzorka provedeno putem metode K-sredina, a mjera siluete korištena je kako bi se pronašao optimalan broj grupa, a to je rezultiralo stvaranjem 13 grupa. Za provjeru postupka odabran je uzorak u svakoj grupi, a na tim uzorcima provedena su ispitivanja izravnog smicanja. Usporedba rezultata ispitivanja i grupiranja pokazala je dobro slaganje, stoga je ova metoda učinkovit alat za kvantitativno utvrđivanje hrapavosti s obzirom na valovitost i neravnine površine

In-situ Micro and Nanomechanical Characterization and Ultrasonic Machining of Zirconia Ceramics

Zirconia ceramics are popular load-bearing ceramics exhibiting superior mechanical, chemical, optical, and biocompatibility properties, suitable for dental applications. These ceramic properties are available in distinct microstructures under pre-sintered and sintered states, respectively. Their mechanical properties, behavior, and deformation are influenced by their distinct microstructures. Zirconia product failure rates are a concern and understanding of the material general properties associated with distinct microstructures at small-scale contact can provide insight into their load-bearing functions. Shaping of these ceramics structures are conducted using dental CAD/CAM diamond machining processes involving micro and nanoscale diamond tools and material contacts, resulting in severe machining-induced damage. Addressing these matters requires a fundamental understanding of the influence of the ceramics distinct microstructures on indentation mechanics, which lays the foundation of generic insight into indentation-induced deformation and material removal mechanisms. Further, a review of the literature has revealed that conventional machining induces severe machining damage; whereas ultrasonic machining is an emerging technology with the capability to reduce such damage, possessing superior machining responses. A comparison of the ceramics machining responses can provide an alternative to using ultrasonic technology for the improvement of product longevity. This thesis has pursued an understanding of the microstructure-property-processing relations of zirconia materials. Hence, a thorough investigation was made into the influence of distinct microstructures in zirconia materials in terms of their micro and nanomechanical responses at small scale length and conventional and ultrasonic machining processes. The first objective of this thesis is an investigation of zirconia materials with distinct microstructures under external load at small-scale contact volume, providing the critical micromechanical properties and behaviors for load-bearing functions. In-situ micropillar compression tests were conducted on pre-sintered and sintered zirconia materials. The two zirconia materials revealed micropillar-induced plastic behaviors with severe buckling occurred more frequently in pre-sintered zirconia than in sintered zirconia. Presintered zirconia showed lower Young’s moduli, strength properties (yield, compression, and fracture) and energy absorption properties (toughness and resilience) but higher ductility, in comparison with sintered zirconia. In addition, different quasi-brittle failure mechanisms were revealed including mushrooming buckling damage with microcracks and severe compaction for pre-sintered zirconia. Plastic crushing damage with microcracks and microfractures in sintered zirconia was also observed. The second objective of this thesis is an examination of the microstructure responses associated with indentation mechanics and behavior of zirconia materials at small-scale contact using sharp diamond indenters simulating tool-sample contact mechanics in dental abrasive machining. In-situ nanoindentation tests combined with an in-situ technique were also conducted on pre-sintered and sintered zirconia materials. The nanoindentation revealed quasi-brittle behavior for both zirconia materials but at the microstructural level different quasi-plastic mechanisms were identified for the two materials. Weak pore interface boundaries in the pre-sintered zirconia resulted in compression, fragmentation, pulverization, and microcracking of zirconia crystals. Shear bands with localized microfractures were induced in sintered zirconia. Pre-sintered zirconia had a lower rank in quasi-plasticity than sintered zirconia, predicting that it is more susceptible to abrasive machining-induced damage than sintered zirconia. The higher indentation volume in pre-sintered zirconia compared with sintered zirconia indicates the pre-sintered state has higher machining efficiency than the sintered state. The third objective of this thesis is the cyclic nanoindentation of the zirconia materials. To further understand diamond machining of zirconia materials, experiments to help with understanding of material responses under repetitive indentation mechanics, which more closely represents the machining process, were conducted. In-situ cyclic nanoindentation tests were performed with 10 repeated loading and unloading cycles. Cyclic nanoindentation induced quasi-plastic deformation for the two zirconia materials with distinct mechanisms of quasi-plasticity. Agglomeration of zirconia crystals, cracks, compresses, and pulverized crystals were revealed in pre-sintered zirconia cyclic indentation imprints. Shear band, edge pile-ups, and microfractures were revealed in sintered zirconia indentation imprints. Advanced analysis of the zirconia materials deformation mechanisms revealed zirconia microstructures determined their cyclic nanoindentation induced deformation, predicting the ease of machining for pre-sintered zirconia but also revealing they may potentially suffer more severe abrasive machining damage than sintered zirconia. The fourth objective of this thesis is to investigate the zirconia materials responses to edge chipping damage induced in conventional and ultrasonic vibration-assisted diamond machining processes. The edge chipping damage observed in zirconia materials largely depends on microstructure and the applied vibration amplitude during machining. Edge chipping damage was more severe in pre-sintered zirconia with weak pore interface boundaries and a higher brittleness index than in dense zirconia with a tightly packed microstructure and a lower index. Ultrasonic machining at an optimum vibration amplitude led to different material removal mechanisms reducing the brittle fracture induced during machining, hence significantly decreasing edge chipping damage and fracture in both zirconia materials. The fifth objective of this thesis is an examination of the microstructural influence of damage-induced surface asperities produced by conventional and ultrasonic vibration-assisted diamond machining processes. The machining-induced surface damage, removal mechanisms, and surface asperities in the processing of pre-sintered and sintered zirconia depend on microstructure and ultrasonic vibration amplitudes. Conventional and ultrasonic milling induced mixed ductile and brittle fracture modes in pre-sintered and sintered zirconia materials. Milled pre-sintered zirconia showed dominant brittle fracture removal mechanism whereas ductile deformation was the dominant mode for sintered zirconia. Milled pre-sintered zirconia surfaces had more fractures and cracks and higher surface asperities than milled sintered zirconia surfaces. At an optimized vibration amplitude in both zirconia materials, ultrasonic machining enabled the minimization of brittle fracture at the micro-scale to result in more ductile deformation, with reduced surface damage and asperities than conventional machining.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 202