Multiscale characterization of mechanical and fracture properties of cortical bone specimens

Bone is a hierarchical material with multiple length scales ranging from mineralized collagen fibrils at the nanoscale, single lamella at the sub microscale, lamellar structure at the microscale, osteons at the mesoscale to a whole bone at the macroscale. Several fracture testing methods are available including the three-point bending test, the compact tension test and the double cantilever test. However, these methods are confined to the macroscopic scale. At the microscopic scale, Vickers Fracture Indentation was proposed. Nevertheless, the study observed instances of varied crack lengths making it irreproducible and thus there is a need for further advancement on the testing front at the lower length scales. The research objective is to measure the fracture properties of bone at the level of osteons and at lower length scales using scratch testing. Cortical Bone Specimens obtained from porcine and bovine femurs have been cut, ground, polished and tested using an arduous experimental procedure. The nature of the fracture observed exhibited a strong anisotropy with toughening mechanisms and a competition between plastic flow and brittle fracture. Scanning Electron Microscopy revealed the presence of micro cracking, crack bridging, crack deflection and flaking or chipping along the length of the scratch. The process of applying nonlinear fracture mechanics methodologies such as the J-integral or the energetic size effect law in the analysis used to determine the fracture toughness of bone was meticulous. The results of this investigation showed not only a coupling between elasticity and fracture characteristics but also a mixed mode fracture involved in the determination of the fracture resistance. The investigation employs scratch tests which determine the fracture properties not only at the microscale but also at the lower length scales due to the scalability of the scratch tests. Furthermore, nanoindentation tests were conducted on cortical bone specimens to determine their mechanical properties. Due to the viscoelasticity and viscoplasticity exhibited by cortical bone specimens, creep induced rate effect studies were carried out and their influence on the fracture properties was studied. The presented research paves the way towards a deeper understanding of the fragility of hard biological tissues. The knowledge gained could be applied to inform novel treatment for bone diseases, prevention of bone brittlement and design of advanced structural materials

A Review on In Situ Mechanical Testing of Coatings

Real-time evaluation of materials’ mechanical response is crucial to further improve the performance of surfaces and coatings because the widely used post-processing evaluation techniques (e.g., fractography analysis) cannot provide deep insight into the deformation and damage mechanisms that occur and changes in coatings’ material corresponding to the dynamic thermomechanical loading conditions. The advanced in situ examination methods offer deep insight into mechanical behavior and material failure with remarkable range and resolution of length scales, microstructure, and loading conditions. This article presents a review on the in situ mechanical testing of coatings under tensile and bending examinations, highlighting the commonly used in situ monitoring techniques in coating testing and challenges related to such techniques

Study of Thin-Film Surfaces

Disertační práce se zabývá studiem povrchových vlastností jedno a vícevrstvých filmů deponovaných z vinyltriethoxysilanových a tetravinylsilanových monomerů. Zabývá se také charakterizací adheze jednovrstvých filmů z tetravinylsilanu. Plazmaticky polymerizované tenké vrstvy byly připraveny na leštěných křemíkových substrátech pomocí plazmové depozice z plynné fáze za ustálených podmínek. Povrchové vlastnosti vrstev byly charakterizovány pomocí různých metod rastrovací sondové mikroskopie a nanoindentačních technik jako je konvenční a cyklická nanoindentace. Vrypový test byl použit pro charakterizaci vlastností adheze vrstev. Jednovrstvé filmy připravené za různých depozičních podmínek byly charakterizovány s ohledem na povrchové morfologie a mechanické vlastností (modul pružnosti, tvrdost). Výsledky morfologie povrchu, analýzy zrn, nanoindentace, analýzy konečných prvků a modulů mapování pomohly rozlišit hybridní charakter filmů, které byly deponovány při vyšších výkonech RF-výboje. Nový přístup byl použit v povrchové charakterizaci vícevrstvého filmu pomocí rastrovací sondové mikroskopie a nanoindentace. Adhezívní chování plazmaticky polymerizovaných vrstev různých mechanických vlastností a tloušťek bylo analyzováno pomocí normálních a laterálních síl, koeficientu tření, a snímků vrypů získaných pomocí mikroskopie atomárních sil.doctoral thesis deals with the study of surface properties of single-layer and multilayer thin films deposited from of vinyltriethoxysilane and tetravinylsilane monomers. It also deals with adhesion characterization of single layer tetravinylsilane films. The plasma polymerized thin films were prepared under steady-state deposition conditions on polished silicon wafers using plasma-enhanced chemical vapor deposition. The surface properties of the films were been characterized by different scanning probe microscopy methods and nanoindentation techniques such as conventional depth-sensing nanoindentation and load-partial-unload (cyclic) nanoindentation. While, the nanoscratch test was used to characterize the film adhesion properties. Single layer films prepared at different deposition conditions were characterized with respect to surface morphology and mechanical properties (Young’s modulus and hardness). The results of surface morphology, grain analysis, nanoindentation, finite elemental analysis and modulus mapping helped to know the hybrid nature of single layer films that were deposited at higher powers of RF-discharge. A novel approach was used in surface characterization of multilayer film by scanning probe microscopy and nanoindentation. The adhesion behavior of plasma polymer films of different mechanical properties and film thickness were analyzed by normal and lateral forces, friction coefficient, and scratch images obtained by atomic force microscopy.

Laser-assisted scanning probe alloying nanolithography (LASPAN) and its application in gold-silicon system

Nanoscale science and technology demand novel approaches and new knowledge to further advance. Nanoscale fabrication has been widely employed in both modern science and engineering. Micro/nano lithography is the most common technique to deposit nanostructures. Fundamental research is also being conducted to investigate structural, physical and chemical properties of the nanostructures. This research contributes fundamental understanding in surface science through development of a new methodology. Doing so, experimental approaches combined with energy analysis were carried out. A delicate hardware system was designed and constructed to realize the nanometer scale lithography. We developed a complete process, namely laser-assisted scanning probe alloying nanolithography (LASPAN), to fabricate well-defined nanostructures in gold-silicon (Au-Si) system. As a result, four aspects of nanostructures were made through different experimental trials. A non-equilibrium phase (AuSi3) was discovered, along with a non-equilibrium phase diagram. Energy dissipation and mechanism of nanocrystalization in the process have been extensively discussed. The mechanical energy input and laser radiation induced thermal energy input were estimated. An energy model was derived to represent the whole process of LASPAN

On-Line Topographic Measurements of Lubricated Metallic Sliding Surfaces

Moderne Methoden wurden kombiniert, um die topographische Änderungen von gleitenden geschmierten metallischen Oberflächen on-line zu untersuchen. Die Experimente wurden mit einem neuartigen Tribometer durchgeführt, welches in-situ topographische Messungen ermöglicht. Die Ergebnisse zeigen, wie lamellare Verschleißpartikel auf gleitende Kupfer Oberflächen entstehen. Weitere Versuche ermöglichten die Entwicklung einer Näherungsmethode zur Trennung von Pflüg- und Scherbeiträge der Reibkraft

On-Line Topographic Measurements of Lubricated Metallic Sliding Surfaces

Moderne Methoden wurden kombiniert, um die topographische Änderungen von gleitenden geschmierten metallischen Oberflächen on-line zu untersuchen. Die Experimente wurden mit einem neuartigen Tribometer durchgeführt, welches in-situ topographische Messungen ermöglicht. Die Ergebnisse zeigen, wie lamellare Verschleißpartikel auf gleitende Kupfer Oberflächen entstehen. Weitere Versuche ermöglichten die Entwicklung einer Näherungsmethode zur Trennung von Pflüg- und Scherbeiträge der Reibkraft

Integrating Nanomechanical Property Testing into a Correlative Imaging Workflow

This work is aimed at creating a cohesive workflow between correlative imaging techniques and nanomechanical property testing for materials analysis. There exist multiple features of a material, on varying length scales, that can determine its performance in its desired function. As technology advances new materials are developed to address new problems with more and more taking their inspiration from nature. The use of different techniques individually has been able to shed light on either the structure, property, or function of the materials, either manufactured or biological. Understanding has developed that the three aspects; structure, property, and function are related and should be considered together when analysing a material. Combining multiple techniques in a workflow will allow for revealing the ‘whole picture’ of the material. The methods of materials analysis used in this research are X-ray micro-CT, scanning electron microscopy (SEM), light microscopy, X-ray fluorescence (XRF), and nanoindentation. Each of the methods used here requires specific preparation methods prior to testing and one testing method may make the sample unsuitable for another testing method. Therefore, planning the sequence of testing before commencing is of high importance. Putting into place a workflow will not only reduce the likelihood of inhibiting further testing procedures but also reduce the time taken for completing a comprehensive analysis. The workflow proposed here takes into consideration what information can be gained as well as preparation techniques. Initially, this thesis will discuss correlative imaging detailing, sample preparation, and the capabilities of these techniques in uncovering the internal nano – to the macro-structure of antler bone and barnacle plate organisation, as well as the chemical uniformity of the inorganic phase of antler bone across the cross-section and the elongated crystallographic structures unique to the barnacle ala. Secondly, XRF will be explored for its role in the chemical analysis of biological materials and where this technique can be placed into the workflow to impact the overall understanding of the chemical composition in this instance in the application of antlers. Finally covered will be nanomechanical property testing for both stand-alone equipment and in-situ indentation. The suggested position for this technique in the workflow will be explained as it is used as the final connecting piece in determining the structure-function-property relationship of the material due to how the previous methods have directed the research process. Correlating the accelerated property mapping technique to the crystallographic structures in barnacle plates showed a reduced hardness in the elongated crystal region. Nanoindentation of the antler bone showed differences in modulus between the transverse and cross-sections as well as a reduction in average hardness between the male antler and the female reindeer that had calves and those that did not. Each of the individual pieces of information in this workflow when brought together unveils the hidden structure-property-function relationship in materials to provide an in-depth understanding

Surface analysis of xGnP/PEI nanocomposite

Tato Diplomová práce se zabývá povrchovou analýzou nanokompozitní folie polyetherimidu (PEI) vyztuženého exfoliovanými grafitickými nanodestičkami (xGnP). Analyzovány byly take vzorky nevyztužené PEI folie a samostatné nanodestičky. Vzorky nanokompozitu a PEI folie byly plazmaticky leptány s využitím argonového plazmatu po dobu 1, 3 a 10 hod. Skenovací elektronová mikroskopie (SEM) byla použita pro charakterizaci samostatných nanodestiček rozptýlených na křemíkovém substrátu, původních či leptaných vzorků PEI folie a nanokompozitu. Nanodestičky byly identifikovány při povrchu leptané nanokompozitní folie. Mikroskopie atomárních sil (AFM) byla použita pro zobrazení povrchové topografie separovaných nanodestiček a odkrytých destiček při povrchu leptaného kompozitu. Povrchová drsnost (střední kvadratická hodnota, vzdálenost nejnižšího a nejvyššího bodu) leptaného nanokompozitu narůstala s prodlužující se dobou leptání. Akustická mikroskopie atomárních sil (AFAM) byla použita pro charakterizaci elastické anizotropie leptaných kompozitních vzorků. Nanoindentační měření umožnila charakterizaci lokálních mechanických vlastností PEI a nanokompozitních folií.This Diploma thesis deals with surface analysis of nanocomposite foil – polyetherimide matrix (PEI) reinforced by exfoliated graphite nanoplatelets (xGnP). The PEI foil without reinforcement and separate xGnP particles were also analysed. Samples of the nanocomposite and the PEI foil were etched for various times by argon plasma. Scanning electron microscopy (SEM) was used to characterize xGnP agglomerates dispersed over silicon wafer and pristine/etched samples of PEI foil and nanocomposite xGnP/PEI foil. Graphite nanoplatelets were identified at surface of etched nanocomposite foil. Atomic force microscopy (AFM) was used for surface topography imaging of separate nanoplatelets and those uncovered at the surface of etched nanocomposite. Surface roughness (root mean square, peak to peak) of etched nanocomposite increased with prolonged etching time. Atomic force acoustic microscopy (AFAM) was used to characterize elastic anisotropy of etched nanocomposite. Nanoindentation measurements were employed to characterize the local mechanical properties of PEI and nanocomposite foils.

NEW METROLOGICAL TECHNIQUES FOR MECHANICAL CHARACTERIZATION AT THE MICROSCALE AND NANOSCALE

New metrological techniques have been developed for mechanical characterization at the microscale and nanoscale as follows: (1) Development of a control system and integrated imaging capability at the microscale and nanoscale for a new biaxial microtensile tester, (2) a new method for characterizing nonlinearity in AFM imaging using Digital Image Correlation (DIC), and (3) development of pointwise DIC technique. In the biaxial microtensile tester, loading of specimen is induced through the opposing motion of dual picomotor linear actuators in orthogonal directions with a displacement resolution of less than 30 nm. Using an optical microscope, in situ digital images are obtained and analyzed with DIC to determine the full field displacements at the microscale over an Area of Interest (AOI) in order to characterize the biaxial performance of the microtensile tester. An objective AFM has been integrated into the biaxial microtensile tester to obtain in situ digital images of topographic microstructural features at the nanoscale. These topographic images can then be converted to gray scale images with textures that are suitable for DIC to calculate full field displacements at the nanoscale. This measurement capability is demonstrated on a sputtered nanocrystalline copper film subjected to uniaxial loading in the microtensile tester. Since image quality is critical to the accuracy of the nanoscale DIC measurements, a new method was developed to calibrate the errors induced by the nonlinearity of AFM scanning. In this new method, the DIC technique was applied to AFM images of sputtered nanocrystalline NiTi films to calculate the displacement errors caused by the probe offset that must be eliminated from the apparent displacement field. The conventional DIC technique assumes a zero-order or first order approximation of the variation in displacement fields (i.e., displacement gradients) relative to the center of a subset of the image. In the case of displacement fields associated with the microstructure of a material, the displacement gradients can vary discontinuously, which violates the assumed nature of the displacement gradients in the conventional DIC. Therefore, a pointwise DIC technique has been developed to calculate displacements independently at each pixel location, eliminating the constraints imposed by the subset on the calculated displacements. Because of the potentially large number of unknown displacement variables that need to be determined using this approach, an efficient Genetic Algorithm (GA) optimization algorithm with a Differential Evolution (DE) method was investigated for optimizing the correlation function. To guarantee uniqueness of the optimized displacement field, the correlation function was modified using intensity gradients that had to be transformed from an Eulerian to Lagrangian reference frame using displacement gradients. The theoretical development of pointwise DIC is discussed in detail using ideal sinusoidal images, and its validation using real images is also presented