Microscale Mechanical Properties Research Articles

Microscale mechanical properties of single elastic fibers: The role of fibrillin–microfibrils

Micromechanical properties of single elastic fibers and fibrillin–microfibrils, isolated from equine ligamentum nuchae using chemical and enzymatic methods, were determined with atomic force microscopy (AFM). Young's moduli of single elastic fibers immersed in water, devoid of or containing fibrillin–microfibrils, were determined using bending tests. Bending freely suspended elastic fibers on a micro-channeled substrate by a tip-less AFM cantilever generated a force versus displacement curve from which Young's moduli were calculated. For single elastic fibers, Young's moduli in the range of 0.3–1.5 MPa were determined, values not significantly affected by the presence of fibrillin–microfibrils. To further understand the role of fibrillin–microfibrils in vertebrate elastic fibers, layers of fibrillin–microfibrils were subjected to nano-indentation tests. From the slope of the force versus indentation curves, Young's moduli ranging between 0.56 and 0.74 MPa were calculated. The results suggest that fibrillin–microfibrils are not essential for the mechanical properties of single vertebrate elastic fibers.

3D material microstructures design and numerical simulation

To study the micro-scale mechanical properties and failure behavior, and achieve the goal of “performance-oriented” design of microstructure and material performance prediction, in this study, computer simulation, micromechanics calculation and virtual failure analysis on microstructures of polycrystalline materials with multi-component and multiphase are realised by means of programming and finite element numerical simulation. Under the condition of creating representative volume element of microstructures of polycrystalline material and polycrystalline matrix composite that are constructed by material microstructure computer simulation software ProDesign, and based on the secondary development of the commercial finite element software ABAQUS, numerical calculation of micro-scale mechanics of microstructures is implemented. The results of the numerical simulation can be used to predict material performance, identify “material structure weakness”, evaluate initialization and propagation of microcracks of microstructures for heterogeneous materials and deduce the behavior of “virtual failure” of microstructure.

Physico-mechanical properties determination using microscale homotopic measurements: Application to sound and caries-affected primary tooth dentin

Microscale elastic moduli, composition and density have rarely been determined at the same location for biological materials. In this paper, we have performed homotopic measurements to determine the physico-mechanical properties of a second primary molar specimen exhibiting sound and caries-affected regions. A microscale acoustic impedance map of a section through this sample was acquired using scanning acoustic microscopy (SAM). Scanning electron microscopy was then used to obtain mineral mass fraction of the same section using backscattered images. Careful calibration of each method was performed to reduce system effects and obtain accurate data. Resorption, demineralization and hypermineralization mechanisms were considered in order to derive relationships between measured mineral mass fraction and material mass density. As a result, microscale mass density was determined at the same lateral resolution and location as the SAM data. The mass density and the acoustic impedance were combined to find the microscale elastic modulus and study the relationship between microscale composition and mechanical properties.

Nanoindentation of biological materials

Nanoindentation has recently emerged as a powerful tool for measuring nano- and microscale mechanical properties in tissues and other biomaterials. This technique has been used to measure the mechanical properties of microstructural features in bone and teeth, investigate variations in mechanical properties with changes in tissue organization or composition in mineralized and soft tissues, and map mechanical properties spatially in complex biomaterials. Continuing advancements in indentation data analysis will increase the method's utility in the characterization of biomaterials.

Parametric study of the effect of phase anisotropy on the micromechanical behaviour of dentin-adhesive interfaces.

A finite element (FE) model has been developed based upon the recently measured micro-scale morphological, chemical and mechanical properties of dentin-adhesive (d-a) interfaces using confocal Raman microspectroscopy and scanning acoustic microscopy (SAM). The results computed from this FE model indicated that the stress distributions and concentrations are affected by the micro-scale elastic properties of various phases composing the d-a interface. However, these computations were performed assuming isotropic material properties for the d-a interface. The d-a interface components, such as the peritubular and intertubular dentin, the partially demineralized dentin and the so-called "hybrid layer" adhesive-collagen composite, are probably anisotropic. In this paper, the FE model is extended to account for the probable anisotropic properties of these d-a interface phases. A parametric study is performed to study the effect of anisotropy on the micromechanical stress distributions in the hybrid layer and the peritubular dentin phases of the d-a interface. It is found that the anisotropy of the phases affects the region and extent of stress concentration as well as the location of the maximum stress concentrations. Thus, the anisotropy of the phases could effect the probable location of failure initiation, whether in the peritubular region or in the hybrid layer.

Effects of heat treatment on the compressive deformation behavior of open cell aluminum foams

This paper presents a study of effects of heat treatment on compressive deformation behavior of Duocel ® open cell aluminum foams in as-fabricated (F), annealed (O) and T6-strengthened (T6) conditions. Following an investigation of the effects of heat treatment on foam strength and stress–strain behavior, heterogeneous nature of the compressive deformation was then elucidated using a combination of experimental investigation and digital image correlation (DIC) technique. DIC analyses were carried out on image sets that were recorded using an in situ digital camera during compressive testing. The significant effects of heat treatment processes on foam compressive strengths, stress–strain behavior, and deformation mechanisms are then attributed to the changes of the microstructure and micro-scale mechanical property of individual struts due to annealing and T6-strengthening processes.

High-temperature nanoindentation testing of fused silica and other materials

Abstract This paper describes a new high-temperature stage for small-scale mechanical property testing. This allows the determination of the load-penetration curve of a diamond tip in a temperature range extending from room temperature to 400°C. Both sample and indenter can be heated separately. Indentation curves show that very low thermal drift can be achieved. Nanoindentation results are presented for gold, soda—lime glass, fused silica and a polyimide and compared with existing microscale and bulk mechanical property data where available. Results from fused silica show that its mechanical properties exhibit a completely different temperature dependence from those of soda-lime glass, as expected since fused silica is an anomalous glass.

Measurement of mechanical properties for MEMS materials

The microscopic mechanical devices in microelectromechanical systems (MEMS) use materials such as silicon and many other thin films, which had not previously been considered mechanical materials and thus are not well characterized regarding their mechanical properties. However, as the field matures, sustained research and commercial development in the coming years will demand better understanding of mechanical properties such as Young's modulus and the fracture strength. Uniaxial tension testing is generally considered the most reliable way to measure the mechanical properties. However, the problems associated with the microscopic size of the test specimen for MEMS, such as sample handling and sample alignment, led to such alternative ways as membrane-bulge testing and natural frequency testing at the beginning of MEMS. In this paper, recent methods for testing microscale mechanical properties and their results are summarized. Many reports, based on two distinct types of test, beam bending and direct tension, are introduced. The efforts to integrate the sample and loading system on the microscopic scale are also explained. Studies of fatigue, the most recent development in microscale measurement of mechanical properties, are discussed. The results from the testing methods described are listed for comparison.

Scanning Probe Microscopy of Polymer Surfaces

Abstract Basic principles and recent results of scanning probe microscopy (SPM) studies of polymer surfaces are reviewed. Applicability of various SPM techniques—including contact, dynamic, force modulation, friction force, chemical force, electrostatic, adhesion, and thermal modes—to probing of polymer surfaces is illustrated. Examples of recent studies of surface morphology and properties of various polymers are presented and briefly discussed. An extensive bibliography of more than 200 references is included. Classes of polymers considered here are: crystalline and amorphous, composites and blends, fibers and deformed polymers, block polymers and latexes, rubbers and liquid crystalline polymers, thin films and ionomers. Current focuses and future trends are summarized including quantitative SPM measurements, probing of nano- and microscale mechanical properties, studying dynamical surface properties, and exploring local chemical interactions.