1,421 research outputs found
Slow dynamics and stress relaxation in a liquid as an elastic medium
We propose a new framework to discuss the transition from exponential
relaxation in a liquid to the regime of slow dynamics. For the purposes of
stress relaxation, we show that a liquid can be treated as an elastic medium.
We discuss that, on lowering the temperature, the feed-forward interaction
mechanism between local relaxation events becomes operative, and results in
slow relaxation.Comment: changed conten
Enhancing the Performance of the T-Peel Test for Thin and Flexible Adhered Laminates
Symmetrically bonded thin and flexible T-peel specimens, when tested on
vertical travel machines, can be subject to significant gravitational loading;
with the associated asymmetry and mixed-mode failure during peeling. This can
cause erroneously high experimental peel forces to be recorded which leads to
uncertainty in estimating interfacial fracture toughness and failure mode. To
overcome these issues, a mechanical test fixture has been designed for use with
vertical test machines, that supports the unpeeled portion of the test specimen
and suppresses parasitic loads due to gravity from affecting the peel test. The
mechanism, driven by the test machine cross-head, moves at one-half of the
velocity of the cross-head such that the unpeeled portion always lies in the
plane of the instantaneous center of motion. Several specimens such as bonded
polymeric films, laminates, and commercial tapes were tested with and without
the fixture, and the importance of the proposed T-peel procedure has been
demonstrated
Elasticity of smectic liquid crystals with focal conic domains
We study the elastic properties of thermotropic smectic liquid crystals with
focal conic domains (FCDs). After the application of the controlled preshear at
different temperatures, we independently measured the shear modulus G' and the
FCD size L. We find out that these quantities are related by the scaling
relation G' ~ \gamma_{eff}/L where \gamma_{eff} is the effective surface
tension of the FCDs. The experimentally obtained value of \gamma_{\rm eff}
shows the same scaling as the effective surface tension of the layered systems
\sqrt{KB} where K and B are the bending modulus and the layer compression
modulus, respectively. The similarity of this scaling relation to that of the
surfactant onion phase suggests an universal rheological behavior of the
layered systems with defects.Comment: 14 pages, 7 figures, accepted for publication in JPC
Observation of non-local dielectric relaxation in glycerol
Since its introduction, liquid viscosity and relaxation time have been
considered to be an intrinsic property of the system that is essentially local
in nature and therefore independent of system size. We perform dielectric
relaxation experiments in glycerol, and find that this is the case at high
temperature only. At low temperature, increases with system size and
becomes non-local. We discuss the origin of this effect in a picture based on
liquid elasticity length, the length over which local relaxation events in a
liquid interact via induced elastic waves, and find good agreement between
experiment and theory
The Effect of a Two-Stage Heat-Treatment on the Microstructural and Mechanical Properties of a Maraging Steel
Maraging steels gain many of their beneficial properties from heat treatments which induce the precipitation of intermetallic compounds. We consider here a two-stage heat-treatment, first involving austenitisation, followed by quenching to produce martensite and then an ageing treatment at a lower temperature to precipitation harden the martensite of a maraging steel. It is shown that with a suitable choice of the initial austenitisation temperature, the steel can be heat treated to produce enhanced toughness, strength and creep resistance. A combination of small angle neutron scattering, scanning electron microscopy, electron back-scattered diffraction, and atom probe tomography were used to relate the microstructural changes to mechanical properties. It is shown that such a combination of characterisation methods is necessary to quantify this complex alloy, and relate these microstructural changes to mechanical properties. It is concluded that a higher austenitisation temperature leads to a greater volume fraction of smaller Laves phase precipitates formed during ageing, which increase the strength and creep resistance but reduces toughness
Elasticity, Stability and Ideal Strength of -SiC in plane-wave-based ab initio calculations
On the basis of the pseudopotential plane-wave(PP-PW) method and the
local-density-functional theory(LDFT), this paper studies energetics,
stress-strain relation, stability and ideal strength of -SiC under
various loading modes, where uniform uniaxial extension and tension, biaxial
proportional extension are considered along directions [001] and [111]. The
lattice constant, elastic constants and moduli of equilibrium state are
calculated, and the results agree well with the experimental data. As the four
Si-C bonds along directions [111], [11], [11] and
[11] are not the same under the loading along [111], internal
relaxation and the corresponding internal displacements must be considered. We
find that, at the beginning of loading, the effect of internal displacement
through shuffle and glide plane diminishes the difference among the four Si-C
bonds length, but will increase the difference at the subsequent loading, which
will result in a crack nucleated on \{111\} shuffle plane and a subsequently
cleavage fracture. Thus the corresponding theoretical strength is 50.8 GPa,
which agrees well with the recent experiment value, 53.4 GPa. However, with the
loading along [001], internal relaxation is not important for tetragonal
symmetry. Elastic constants during the uniaxial tension along [001] are
calculated. Based on the stability analysis with stiffness coefficients, we
find that the spinodal and Born instabilities are triggered almost at the same
strain, which agrees with the previous molecular dynamics simulation. During
biaxial proportional extension, stress and strength vary proportionally with
the biaxial loading ratio at the same longitudinal strain.Comment: 9 pages, 10 figure
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