Use Of Microindentation Research Articles

Fracture risk assessment in diabetes mellitus.

Growing evidence suggests that diabetes mellitus is associated with an increased risk of fracture. Bone intrinsic factors (such as accumulation of glycation end products, low bone turnover, and bone microstructural changes) and extrinsic factors (such as hypoglycemia caused by treatment, diabetes peripheral neuropathy, muscle weakness, visual impairment, and some hypoglycemic agents affecting bone metabolism) probably contribute to damage of bone strength and the increased risk of fragility fracture. Traditionally, bone mineral density (BMD) measured by dual x-ray absorptiometry (DXA) is considered to be the gold standard for assessing osteoporosis. However, it cannot fully capture the changes in bone strength and often underestimates the risk of fracture in diabetes. The fracture risk assessment tool is easy to operate, giving it a certain edge in assessing fracture risk in diabetes. However, some parameters need to be regulated or replaced to improve the sensitivity of the tool. Trabecular bone score, a noninvasive tool, indirectly evaluates bone microstructure by analyzing the texture sparsity of trabecular bone, which is based on the pixel gray level of DXA. Trabecular bone score combined with BMD can effectively improve the prediction ability of fracture risk. Quantitative computed tomography is another noninvasive examination of bone microstructure. High-resolution peripheral quantitative computed tomography can measure volume bone mineral density. Quantitative computed tomography combined with microstructure finite element analysis can evaluate the mechanical properties of bones. Considering the invasive nature, the use of microindentation and histomorphometry is limited in clinical settings. Some studies found that the changes in bone turnover markers in diabetes might be associated with fracture risk, but further studies are needed to confirm this. This review focused on summarizing the current development of these assessment tools in diabetes so as to provide references for clinical practice. Moreover, these tools can reduce the occurrence of fragility fractures in diabetes through early detection and intervention.

Coupling multi-scale mechanical testing techniques reveals the existence of a trans-granular channel fracture deformation mechanism in high dose Inconel X-750

Recent testing has shown that Inconel® X-750 materials have lost strength and ductility following irradiation, which may raise concerns over the structural integrity of the material. Bulk component compression testing shows irradiation temperature has a clear influence on mechanical behaviour; material irradiated at higher temperatures exhibits less ductility compared to material irradiated at lower temperatures. This has been re-affirmed with the most recent large scale compression testing of material irradiated to doses between 70 dpa and 80 dpa. Measuring material yield strength from this data has proven to be challenging, due to the complex geometry of the material and the testing methodology. This work outlines the use of micro-indentation, and novel small-scale micro-mechanical testing to measure the mechanical properties of neutron irradiated Inconel X-750 material. The results and conclusions provide valuable insights into the mechanical property evolution, and embrittlement of the material. Microhardness and micro-mechanical testing have confirmed that material irradiated at lower temperatures has a lower yield strength, lower critical resolved shear stress (CRSS), and higher plasticity. The current results confirm the existence of an additional mechanism of crack initiation not previously considered for Inconel X-750 material. In addition to intergranular fracture, re-examination of component-scale test fracture surfaces also reveals that some portion of the component fails via transgranular, faceted pathways. Transmission electron microscopy (TEM) of deformed micro-tensile specimens has confirmed channel fracture. When subject to a slip band or dislocation channel, helium bubbles within the grain interior shear along the slip direction and coalesce prior to shearing the ligaments between the bubbles. The two deformation mechanisms are expected to interact in the bulk material. When discrete flow localization events (dislocation channels) intersect compromised grain boundaries decorated with helium bubbles, they will be expected to produce significant stresses which drives fracture propagation along the grain boundary.

High resolution two-dimensional dose mapping of electron beam processed polymers

The recent advances in electron beam processing of polymer samples require increasingly dose mapping techniques with depth and volume resolution capability. In this paper, the use of micro-indentation and thermo-mechanical analysis is proposed to fulfill the necessary requirements in terms of resolution and accuracy. Experimental procedures are used to acquire mechanical data that are successively converted into dose levels based on dedicated calibrated samples. Physical principles, experimental artifacts, and limitations are discussed with special focus on calibration and validation of a simulator for dosimetry in electron beam cross-linking of electrical cables.

Use of microindentation to characterize the mechanical properties of articular cartilage: comparison of biphasic material properties across length scales

Small scale mechanical testing techniques offer new possibilities for defining changes in mechanical properties that accompany the morphological, histological, and biochemical abnormalities of osteoarthritis (OA). The goal of this study was to investigate the use of microindentation in characterizing the biphasic material properties of articular cartilage. Direct comparisons of the biphasic properties (E, k and nu) determined using microindentation were made to those determined on the same specimens using standard macroscale testing techniques. Deep-zone bovine articular cartilage specimens (n=10) were tested in macroscale confined and unconfined compression. For microindentation testing, the biphasic properties were determined by conducting finite element simulations of the microindentation experiments for different combinations of values of biphasic properties and identifying the combination yielding the best match to each microindentation curve. Paired t-tests were performed to compare each of E, k and nu between the macro- and microscale. The microscale values for E, k and nu were 0.74 (0.53, 0.95)MPa, 0.66 (0.022, 0.110)x10(-16)m(4)/Ns, and 0.16 (0.08, 0.24), respectively. A significant difference between the macro- and microscale measurements was observed for k (P<0.0001), but not for E or nu (P=0.88, 0.16). The agreement in Young's modulus and Poisson's ratio between the results of the microindentation and macroscale tests supports the use of microindentation for characterization of some of the biphasic material properties of articular cartilage. The observed differences in permeability between macro- and microscales are consistent with evidence in the literature of a length-scale dependence to this property.

About the use of micro-indentation to determine the constitutive material’s mechanical behaviour of cellular structures

Architectured cellular materials seem to be very promising materials since they can combine interesting specific mechanical, acoustical and thermal properties. Nevertheless the process routes used to elaborate such materials, especially the thermal treatments and the added compounds, may alter their constitutive materials for which the mechanical behaviour becomes unknown. In order to determine locally the mechanical behaviour of the constitutive materials of cellular structures we propose the use of microindentation. The model structures considered here are brazed tube stackings. Macroscopic tensile tests and micro-indentation measurements have been performed on isolated tubes having been submitted to different thermal treatment durations. The mechanical properties estimated thanks to both methods show a good agreement. These results also put in evidence the strong influence of the thermal treatment on the behaviour of the constitutive material of the tubes. Micro-indentation measurements performed in the braze joints gave access to their mechanical properties which are strongly heterogeneous. A comparison between the experimental mechanical response of the tube stackings under compression and the one predicted by the finite-element method is proposed too.

Plasticity of indium antimonide between −176 and 400 °C under hydrostatic pressure. Part I: Macroscopic aspects of the deformation

Indium antimonide (InSb) single crystals have been plastically deformed between −176 and 400 °C, i.e. below and above the brittle-to-ductile transition temperature situated around 150–160 °C, via the use of microindentation below room temperature (RT) and the Paterson press (compression under gaseous pressure) above RT. The evolution of the macroscopic mechanical data (hardness and critical resolved shear stress) with temperature suggests the existence of three deformation regimes with transitions at T tr1 = 150 °C and T tr2 = 20 °C. T tr1 coincides with the brittle-to-ductile temperature, while T tr2 may coincide with a transition in the nature of dislocations with dislocations propagating in the glide set above T tr2 while moving in the shuffle set below T tr2.

A microindentation technique for determining strength of solder interface with silver metallization on Co-fired multilayer ceramic substrate

The use of microindentation to determine the strength of a solder interface was explored in low-temperature co-fired multilayer ceramic packages. Microindentations were made on cross-sections of multilayered structures at small stand-off distances from the interface under different indentation loads. Cracking behavior of the interface was observed following indentations. At low indentation loads and large stand-off distances, well-known indentation crack systems developed in the ceramic. Higher indentation loads and smaller stand-off distances resulted in interfacial cracking. It is demonstrated that the indentation condition at the onset of the interfacial cracking may be used as a measure of the interfacial strength.

Stress-Induced Phase Transformation of ZrO2 in ZrO2 (3mol%Y 2O 3)-25vol%Al 2O 3 Composite Studied by Transmission Electron Microscopy

To improve mechanical properties, fracture toughness in particular, ZrO{sub 2} ceramic has been widely used not only as a matrix, but also as a toughening agent. Among them, recently, the ZrO{sub 2}-Al{sub 2}O{sub 3} system has received much attention because of the applications to wear and tool materials in the Al{sub 2}O{sub 3}-rich part and superplastic deformation behavior at the high temperature in the ZrO{sub 2}-rich part. Furthermore, recent availability of high pure and fine-grained ZrO{sub 2} and Al{sub 2}O{sub 3} powders makes it possible to synthesize the composites with submicron size grains by pressureless-sintering at the comparatively low temperature of 1,450 C. The purpose of the present work is to investigate the stress-induced t-m phase transformation of ZrO{sub 2} in the ZrO{sub 2}(3mol%Y{sub 2}O{sub 3})-25vol%Al{sub 2}O{sub 3} bulk composite made by the use of micro-indentation. In addition, the fracture characteristic was studied by the observation of fracture surface made by 3-point bending test.