Computational mechanics strain

Since molecular mechanics "strain energy" calculations (43, 44) have become a valuable tool in interpretation of molecular structure results from crystallographic studies, certain computing techniques used there will be mentioned. The method is simple in principle the strain energy of a particular conformation of a molecule is expressed as the sum of terms of several types, each related to certain structural parameters for example, bond length, non-bonded contacts, torsion angle. 

An alternate, simple technique for assessing thermal durability is to compute the thermal shock parameter from physical properties. This parameter, defined by Eqs. (38) and (39) is the ratio of mechanical strain tolerance to thermal strain imposed by the radial temperature gradient. The higher this parameter is, the better the thermal shock capability will be. 

Molecular dynamics simulations have been used in a variety of ways. They can be used to compute mechanical moduli by studying the response of a model of the bulk polymer to a constant stress or strain, and to study the diffusion of molecules in membranes and polymers.There are numerous biomolecular applications. Structural, dynamic, and thermodynamic data from molecular dynamics have provided insights into the structure-function relationships, binding affinities, mobility, and stability of proteins, nucleic acids, and other macromolecules that cannot be obtained from static models. 

The ion concentrations and the electric potential inside these materials can be computed by the chemical and the electrical field equations. The local concentration differences form an osmotic pressure difference which results in a mechanical strain. Based on this, the swelling/bending of the polymer gel film may be obtained. 

Piezoelectric devices are used in the following areas Measurement of pressure, measurement of vibrations, stress gauge, strain gauge, measurement of acceleration, impact detector, position sensors. There is a wide choice of materials and material forms that are actively piezoelectric. Most of them have the ability to convert mechanical strain into an electrical charge when used as sensor, and to do the opposite when used as an actuator. Studies of piezoelectric semiconductors, nonlinear effects and surface waves led to constraction of useful devices. The research of sophisticated electroacoustic devices may one day simplify the dialogue between the user and the computer. There are matty more examples of this kind one coirld mention. 

Once requiring minicomputers and worksta tions many molecular mechanics programs are avail able for personal computers The information that strain energy calculations can provide is so helpful... 

A number of theoretical (5), (19-23). experimental (24-28) and computational (2), (23), (29-32). studies of premixed flames in a stagnation point flow have appeared recently in the literature. In many of these papers it was found that the Lewis number of the deficient reactant played an important role in the behavior of the flames near extinction. In particular, in the absence of downstream heat loss, it was shown that extinction of strained premixed laminar flames can be accomplished via one of the following two mechanisms. If the Lewis number (the ratio of the thermal diffusivity to the mass diffusivity) of the deficient reactant is greater than a critical value, Lee > 1 then extinction can be achieved by flame stretch alone. In such flames (e.g., rich methane-air and lean propane-air flames) extinction occurs at a finite distance from the plane of symmetry. However, if the Lewis number of the deficient reactant is less than this value (e.g., lean hydrogen-air and lean methane-air flames), then extinction occurs from a combination of flame stretch and incomplete chemical reaction. Based upon these results we anticipate that the Lewis number of hydrogen will play an important role in the extinction process. 

An apparatus for measuring the dynamic modulus and hysteresis of elastomers. The stress-strain oscillogram is shown on a ground-glass screen by means of an optical system. Now superseded by modem computer controlled servo hydraulic and dynamic mechanical thermal analysis machines. Roll Bending... 

Fig. 8. Reconstruction of Young s modulus map in a simulated object. A 3D breast phantom was first designed in silico from MR anatomical images. Then a given 3D Young s modulus distribution was supposed with a 1 cm diameter stiff inclusion of 200 kPa (A). The forward problem was the computing of the 3D-displacement field using the partial differential equation [Eq. (5)]. The efficiency of the 3D reconstruction (inverse problem) of the mechanical properties from the 3D strain data corrupted with 15% added noise can be assessed in (B). The stiff inclusion is detected by the reconstruction algorithm, but its calculated Young s modulus is about 130 kPa instead of 200 kPa. From Ref. 44, reprinted by permission of Wiley-Liss, Inc., a subsidiary of John Wiley Sons, Inc.

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