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Coupled effects between constrained flow, increased strength as a function of decreased sample size, and resulting high stresses affect both modulus and fracture toughness. For submicron size crystalline spheres [ 1 , 2 ], boxes [ 3 ], and cubes [ 4 ], we have recently shown that dislocation by dislocation events can be followed using a combination of AFM/nanoindentation. This has led to at least three proposed strengthening mechanisms for hardening of small constrained volumes under compression[ 4 ]. With the increased stresses, this can produce increased moduli of elasticity in confined volumes small in three dimensions. With increased constrained plasticity this produces increased strength in volumes small in three, two or one dimensions.

Biological materials comprising mineralized tissues, such as bone and dentin in teeth, have hierarchical structures with characteristic length scales ranging from nanometers to millimeters. In this presentation, in vitro fracture toughness and fatigue-crack propagation properties of dentin and human cortical bone are examined from a perspective of discerning how these properties depend upon such microstructural hierarchies. The motivation for this is that although there is substantial clinical interest in their fracture resistance, there is relatively little mechanistic information available on how bone and teeth derive their resistance to cracking and how this is affected by cyclic loads. Specifically, in vitro experiments are described that establish that the initiation of fracture is locally strain-controlled (Nalla et al . [ 1 ]) and that subsequent crack growth (characterized by resistance-curve behavior) is associated with a variety of extrinsic toughening (crack-tip shielding) mechanisms, most importantly crack bridging (from individual collagen fibrils and especially “uncracked ligaments”), macroscopic crack deflection and to a lesser extent diffuse microcracking (Fig. 1) (Kruzic et al . [ 2 ], Nalla et al . [ 3 ]).

The effectiveness of carbon nanotubes (CNTs) as reinforcements is designated by their mechanical behavior as stand alone units. One of the most commonly present topological defects, whose effect on the mechanical behavior of CNTs needs to be clarified, is the Stone-Wales (SW) defect. In this paper, the effect of SW defect on the tensile behavior and fracture of armchair, zigzag and chiral single-walled carbon nanotubes (SWCNTs) was investigated using an atomistic-based progressive fracture model (PFM).

Vibrations and noise exist in almost every aspect of our life and are usually undesirable in engineering structures [ 1 ]. Vibrations are of concern in large structures such as aircraft either civil (airbus A 380) or military, as well as small structures such as electronics [ 2 ]. It is now accepted that nanotechnology can help solve vibration damping and high noise issues through the utilisation of nanomaterials (or media) that dissipate a substantial fraction of the vibration energy that they receive. The mechanisms involved in such materials need to be understood and the relevance to damping identified via both computational and experimental benchmarks.

Thin ionomer membranes showing nanostructure phase separation are widely used in low temperature fuel cells as electrolytes. Examples include perfluorinated sulfonic acid (PFSA) ionomers, better known as Nafion™ produced by E. I. du Pont de Nemours and Company. Their electrochemical performance and mechanical strength properties are determined by their molecular morphology, which resembles water-filled hydrophilic micellae (4∼5nm in size) dispersed in a hydrophobic matrix. Temperature and humidity are two major parameters in an internal fuel cell working environment, which have significant influence on this nanostructure and consequently influence the material properties. The transport properties of such ionomers have been extensively studied. In this paper, we will discuss fracture and strength of such membranes, as related to humidity and temperature.

Radio frequency (RF) switches are one of many MEMS devices that make it possible to communicate, sense, and measure while using minimal amount of space and very low power. The RF microswitches have either capacitive or resistive configuration. The capacitive switches use a flexible membrane design, in which capacitance between two electrodes is induced via electrical voltage; reaching threshold capacitance activates the switch, which enables transmission of a signal. The resistive switches, on the other hand, make direct metal to metal contact. Such design usually uses a cantilever beam that bends as voltage is applied to the two electrodes.

Accompanied with sophistication of the technology of creating surface, multi-layered structures of film tend to increase for improving the accuracy with a large degree of the freedom playing an important role. In particular, various kinds of methods for producing film have been proposed and the application range of film has become wider. In this research, focusing on coating film materials fabricated using PVD, CVD and a combined method of PVD+CVD, grasping their surface morphology is aimed. On the other hand, the reliability of such a new material with a different property between the surface function and the interface function is required. Accordingly, different techniques from conventional methods of evaluating functions of laminated material are needed. Therefore, in this research, so-called textured materials with new structure coated by a series of carbon film or titanium nitride film as described in the following, were selected. The effect of applied impact loading on the adhesion and the interface quality of their films was investigated by observation using laser confocal microscope and fractal dimensional analysis of cracks or exfoliation surfaces.

In dynamic fracture testing the precise determination of the onset of crack initiation is crucial in order to obtain characteristic quantities of the material. This task can be solved easier in case of brittle fracture since brittle fracture is usually accompanied by a sudden drop in the force signal. But in case of ductile fracture or if stable crack propagation occurs before unstable one, the instant of crack initiation cannot be determined directly from the force signal. In these cases additional measurement techniques should be applied. The magnetic emission technique has been proved for detecting brittle crack initiation of ferromagnetic materials [ 1 ]–[ 3 ].

The mechanical strength of polycrystalline metals is frequently associated with the propagation of defects present in their structure as cracks or dislocations. Nevertheless, when these defects are absent, the crystal lattice becomes decisive and the strength is determined by the stress at which the lattice losses its stability. This stress is known as the ideal strength, Clatterbuck et al. [ 1 ], Krenn et al. [ 2 ], and it is especially relevant in experimental situations where there are few mobile defects.

The ASTM standard method for the measurement of fracture toughness, E 1820 [ 1 ], covers procedures and guidelines for the determination of this material property in metallic materials using the parameters K, J or CTOD . The fracture toughness may be measured as a point value, or as a complete fracture toughness resistance curve. In the latter option a J - or CTOD -based resistance curve may be obtained from a single specimen fracture test, in which the crack length is measured from compliance changes, and later verified by optical measurements. The single specimen J-R curve construction procedure defined in E1820 involves several steps, which go from obtaining and plotting the raw J-Δa data, to calculating an interim value of J , termed J _Q, to finally qualifying J _Q as J _Ic, a size-independent value of fracture toughness.