Large Elastic Stiffness Research Articles

Profound softening and shear-induced melting of diamond under extreme conditions: An ab-initio molecular dynamics study

Diamond retains original crystal form and large elastic stiffness up to very high temperatures, and strengthens considerably under high pressures. These remarkable characters dictate its behaviors under extreme loadings such as those in laser-heated diamond anvil cells (LHDACs) or giant planetary interiors. Here we report surprising findings from ab initio molecular dynamics simulations revealing that diamond's mechanical strengths reduce precipitously at elevated temperatures, by 50% at 3000 K, despite that its elastic parameters remain little changed. Our results also unravel an extraordinary shear-induced reduction of melting temperature of diamond under (111)[112¯] shear strains by as much as 1150 K, greatly altering its pressure-temperature (p−T) phase diagram when shear deformations exist. These new benchmarks offer crucial insights for elucidating extreme mechanics of diamond at high p-T conditions, advancing fundamental knowledge with major implications for LHDAC operation and planetary modeling.

Elastic properties and frequency performance of a novel 3–0-type three-component composite

A three-component 3–0-type composite based on the ferroelectric PZT-type ceramic is studied to show the elastic properties and their links to the piezoelectric properties and resonance frequencies. The corundum ceramic is used as a component with a large elastic stiffness, and in the presence of this component, almost equal volume fractions of corundum mc and air pores mp are achieved at 0.05 < mc < 0.18. This influences the elastic and other properties of the studied composite. Experimental results on its performance are interpreted in terms of a model wherein an interaction between the 3–0 ferroelectric ceramic/corundum and 3–0 ferroelectric ceramic/air regions plays the important role. A correlation between the elastic and piezoelectric anisotropy factors is observed, and the anisotropy of the piezoelectric coefficients / ≈ −4 is stated at mc > 0.10. The studied composite is of interest as an active element of piezoelectric transducers and sensors.

Piezoelectric sensitivity and electromechanical coupling in a novel corundum-containing 3–0-type composite

A novel 3–0-type composite, that contains ferroelectric (PZT-type) and corundum ceramics, is studied to show features of the piezoelectric response and anisotropy of electromechanical coupling factors. The corundum ceramic is applied as a component with a large elastic stiffness. Almost equal volume fractions of corundum mc and air pores mp are detected at 0.05 < mc < 0.18, and this has no analogies among the studied piezo-active 3–0-type composites. Experimental results on the piezoelectric coefficients , thickness electromechanical coupling factor , planar electromechanical coupling factor , and anisotropy (and ) are interpreted in terms of a model that takes into account features of the composite microgeometry and an interaction between the 3–0 ferroelectric ceramic/corundum and 3–0 ferroelectric ceramic/air regions. The studied 3–0-type composite can be of interest as an active element of piezoelectric transducers, sensors, and other piezotechnical devices.

Piezoelectric properties and related parameters of a novel 3–0-type composite

The piezo-active 3–0-type composite that contains the ferroelectric ceramic of the PZT type (main piezoelectric component) and corundum ceramic as a component with a large elastic stiffness is first studied within a range of small volume fractions [Formula: see text] of the corundum component. In the composite samples, almost equal volume fractions of corundum [Formula: see text] and air pores [Formula: see text]are detected at [Formula: see text], and this has no analogies among the studied 3–0-type composites. Results on the piezoelectric response, anisotropy of the piezoelectric coefficients [Formula: see text] and electromechanical coupling factors [Formula: see text]/[Formula: see text] are interpreted within the framework of models put forward, and agreement between the evaluated and experimental parameters at [Formula: see text] is observed. The studied composite can be suitable for transducer, ultrasonic and other applications.

Fracture toughness measurement of ultra-thin hard films deposited on a polymer interlayer

The fracture toughness of 100nm-thick chromium nitride films deposited on a soft interlayer is evaluated using two different test methods. Both methods take advantage of the enhanced crack driving force resulting from the large elastic stiffness mismatch between the film and the polymer interlayer. The first method is based on the presence of channel cracks developing during the deposition as a result of large internal stress. The second method relies on nanoindentation induced cracking. The presence of a soft interlayer is shown to be essential to promote cracking otherwise impossible on a hard substrate, hence to determine the fracture toughness of very thin films. The assumptions underlying the two methods are very different, which allows critical cross comparison and assessment. A fracture toughness value between 1.5 and 2MPa·m1/2 is obtained.

Evaluation of the response modification coefficient and collapse potential of special concentrically braced frames

ABSTRACTSpecial concentrically braced frames (SCBFs) are commonly used for seismic design of buildings. Their large elastic stiffness and strength efficiently sustains the seismic demands during smaller, more frequent earthquakes. During large, infrequent earthquakes, SCBFs exhibit highly nonlinear behavior due to brace buckling and yielding and the inelastic behavior induced by secondary deformation of the framing system. These response modes reduce the system demands relative to an elastic system without supplemental damping using a response modification coefficient, commonly termed the R factor. More recently, procedures put forth in FEMAP695 have been made to quantify the R factor through a formalized procedure that accounts for collapse potential. The primary objective of the research in this paper was to evaluate the approach for SCBFs. An improved model for SCBFs that permits simulation of brace fracture was used to conduct response history analyses. A series of three‐story, nine‐story and 20‐story SCBFs were designed and evaluated. Initially, the FEMAP695 method was conducted to estimate collapse and the corresponding R factor. An alternate procedure for scaling the multiple acceleration records to the seismic design hazard was also evaluated. The results show significant variation between the two methods. Of the three variations of buildings studied, the largest vulnerability was identified for the three‐story building. To achieve a consistent margin of safety against collapse, a significantly lower R factor is required for the low‐rise SCBFs (three‐story), whereas the mid‐rise and high‐rise SCBFs (nine‐story and 20‐story) may continue to use the current value of 6, as provided in ASCE‐07. Copyright © 2013 John Wiley &amp; Sons, Ltd.