Application of faraday's effect in static and dynamic holographic photoelasticity

The basic principle of applying Faraday's effect to achieve the separation of fringes in static and dynamic holographic photoelasticity, and a study and application of Faraday's light rotator are described in this paper. It is proposed that Faraday's light rotator be used for automating photoelastic instrumentation for measuring isoclinics and the decimal orders of isochromatic fringes.     

Epon 828 epoxy: A new photoelastic-model material

The photoelastic properties of Epon 828 are discussed. The epoxy is evaluated experimentally for its time-edge effect, optical creep, stress-optic relations, and mechanical properties at room and elevated temperatures. Epon 828 is extremely clear, has good transparency, and can be use for photoelastic stress analysis at room and elevated temperatures. It has a low-fringe constant at room temperature as well as at elevated temperatures coupled with a high critical modulus of elasticity. Epon 828 can easily be cast stress-free and has relatively small amounts of optical and mechanical creep. The machining characteristics of Epon 828 are excellent and it cements easily with itself and other epoxy materials.     

The rheological behaviour of HDPE/LDPE blends

The rheological behaviour of three types of HDPE/LDPE blends at several compositions (various weight percentages of LDPE) has been studied with the aid of a capillary rheometer and three different capillaries. In particular, entrance effects and shear viscosities have been determined over a wide shear rate region and at different temperatures. Thus activation energies could also be evaluated. Synergistic effects are evidenced when the relevant properties of the homopolymers parents are not too different from one another.     

Strain-gage-stability measurements for years at 75°C in air

The authors have evaluated the performance of three types of metal-foil strain gages for two and a half years at a constant temperature of 75°C in air. The studies included polyimide-backed and phenolic-glass-backed gages with copper-nickel foil (constantan) and glass-fiber-rein-forced epoxy-phenolic-resin-backed gages with nickel-chromium foil (modified Karma). All gages were tested in a three-wire-lead, single-active-gage Wheatstone bridge system at nominal mechanical-strain levels of 0, +1000 and ?1000 μm/m. The polyimide-backed constantan gages used in Installation No. 1 typically zero-shifted more than +200 μm/m after 30 days' testing at 75°C. The phenolic-glass-backed constantan gages used in Installation No. 2 zero-shifted ?40 to +20 μm/m after 30 days and +270 to +350 μm/m after 900 days. The glass-fiber-reinforced, epoxyphenolic-resin-backed Karma gages used in Installation No. 3 zero-shifted about +5 μm/m after 30 days, and +20 to +45 μm/m after 900 days. The Karma gages used in Installation No. 3 performed better than the other two types of gages. The measured results for the Karma gages appeared to be independent of the adhesives, test-part material, and mechanical-strain levels that we tested. The high stability and low zero drifts of this gage at 75°C allowed us to reliably correct the measured static-strain data on actual test parts.     

Calculation of the rotational transition probabilities of diatomic molecules when they collide with heavy particles

The collisional rotational transition probabilities for molecule-molecule and molecule-atom interactions in three-dimensional space are calculated. The quasiclassical approach developed in [1] is used. Expressions are obtained that are suitable for practical calculations of single-quantum and double-quantum rotational transitions in diatomic molecules. The collisional rotational transition probabilities are averaged over the Maxwell velocity distribution and their dependence on the gas temperature is obtained. To illustrate the method the results of a calculation of the probabilities for HCl-HCl, HCl-He, CO-CO interaction are presented.     

A composite three-dimensional photoelastic method

Care must be taken in preparation and testing of three-dimensional composite photoelastic models. Some problems encountered in modeling the prototype and during model testing are: model-material failure, loss of fringe pattern in slicing, inherent shrinkage response in freezing, inadequate bonding between materials, and modular ratio difficulties. The selection of the correct plastic can eliminate the first four problems, but the correct modular ratio between the matrix and the insert has to be obtained. This investigation illustrated the behavior of commercially manufactured plastics as inserts, with a matrix material of Epon 828 epoxy. The effective moduli of elasticity of these plastics are reported for pure tension and for flexure. Since the manufactured plastics produced varying results, the use of Epon 828 epoxy as an insert was investigated. The inserts were cast in tygon tubing and their curing cycle was altered from that used for the matrix material to produce a different effective modulus of elasticity. The Epon 828 inserts gave excellent results in the beams. The use of the same material for matrix and insert eliminates many of the problems associated with composite three-dimensional photoelasticity.     

The effect of a coupling agent on the viscoelastic properties and internal stresses in high density polyethylene filled with glass spheres

It is shown that covalent bonding between high density polyethylene (HDPE) and glass spheres can have a significant influence on the stress relaxation behaviour and the creep properties of the corresponding composites at room temperature. The bonding is obtained by reacting the glass spheres with an azide functional alkoxysilane which is capable of bonding to the HDPE-chain. The internal stress, evaluated from relaxation experiments, increased markedly as a result of this treatment, and it is suggested that the internal stress level reflects the properties of the interphase region between the filler and the bulk matrix and its effect on the viscoelastic properties.     

Numerical investigation of the instability of a shear discontinuity of the velocity in compressible gases

A numerical investigation is made of the nonlinear stage of development of the Kelvin-Helmholtz instability in the case of compressible gases.     

The grid-shift technique for moiré analysis of strain in solid propellants

Moiré principles and procedures were surveyed with a view toward adaptation to measurement of complex strain distribution in solid propellants. Compliant coating and photosensitive materials were selected for grid reproduction. The most flexible of the several possible procedures for recording moiré data was found to be grid photography. A novel “grid-shift” technique employing coarse grids was developed for point-by-point determination of surface displacement derivatives, and the grid-shift relations for large strain and large rotation were derived. The technique is extremely versatile, permitting the analysis of strain of dynamically deformed specimens in nonambient environmental conditions of temperature, pressure or atmosphere. The utility of the technique was demonstrated by application to static and dynamic problems.     

An experimental study of food melt rheology. II. End pressure effects

A twin-screw extruder-fed slit die viscometer (SDV) and a piston capillary rheometer have been used to measure the end pressure losses of a low density polyethylene, maize grits and potato powder. The entrance and exit pressure losses have been measured as a function of extrusion conditions. The entrance pressure losses were found to be less than 10% of the total pressure drop in the SDV for LDPE and maize grits. For the potato material, this loss was found to be as large as 58%. The exit pressures for the potato were between 10–20% of the total pressure drop compared to negligible values for the maize and LDPE. Various approaches due to Bagley, Han and Cogswell were used to investigate the elastic properties of these materials.     

An exploratory investigation of cumulative shock fatigue

A simple device for producing cumulative shock loading in solids is described. The device uses a ballistic-impact-driven projectile to introduce high-stress waves into a solid. The impact time and load amplitude can be varied to produce fracture in one or several impacts in PMMA rods. The wavefront approached a square wave shape. Materials other than PMMA were loaded to failure to demonstrate the versatility of the device. Fracture morphologies observed with optical and scanning-electron microscopy are described.     

Machining unreinforced polymers with high-velocity water jets

Sapphire nozzles of 0.076-mm to 0.178-mm diameter have been used with a water intensifier, operating at pressures up to 4.2 kbar, to produce continuous jets with velocities around 6.6×10⁴ cm/s. These jets have been used to machine (slit) sheet specimens of polymethylmethacrylate (PMMA), polycarbonate and acetal at feed rates up to 4 cm/s. A previous paper describes the jet cutting system and analyzes data for PMMA and a phenolic laminate. This paper presents and analyzes data for polycarbonate and acetal; it also reanalyzes the PMMA data. A cutting theory described previously is modified and extended so that depth of cut can be directly related to nozzle pressure, jet flow rate, specimen feed rate and nozzle diameter. In its original form, this energy theory cannot account for the effect of changes in nozzle diameter. It is shown that there is excellent agreement between the predictions of the modified theory and the experimental data. The theory is also used to explain the surface appearance of a typical cut.     

Strain behavior of pressurized cracked thick-walled cylinders

External circumferential strains were measured on large thick-wall pressure vessels containing internal fatigue cracks, using bonded strain gages. When strains measured over the cracks become compressive they predict impending failure. Normalization by the Lamé strain relates them to the fraction of fatigue life consumed and provides estimates of longevity.     

Strain gages in cryogenic environment

The increasing use of cryogenics in all fields of endeavor necessitates the use of strain gages for stress analysis of structures under extreme temperatures. This has been a continuing program at the McDonnell Douglas Astronautics Co.'s Strain Gage Engineering Laboratory (Huntington Beach facility). Many characteristics of strain gages were investigated, and a majority of the commercial strain gage types were evaluated. Tests results are presented, as well as composite curves, showing the comparison between various types of strain gages.     

A image encryption scheme based on dynamical perturbation and linear feedback shift register

Because low-dimensional chaotic precision degradation has seriously affected the security of encryption, compound chaotic function is designed. It is based on two new one-dimensional chaotic functions. By the definition of Devaney chaotic, the properties of compound chaotic functions are rigidly proved. Based on the compound chaotic function and linear feedback shift register (LFSR), a new pseudo-random sequence generator is designed to generate a more random sequence and expand the key space. The properties of compound chaotic functions and LFSR are also established. In the scheme, a dynamic block division of the 3D baker and dynamical perturbation are illustrated using the compound chaotic map to derive the confusion image. The new pseudo-random sequence generator expands the key space and improves the security of image encryption scheme. The results of entropy analysis, difference analysis, weak-key analysis, statistical analysis, cipher random analysis, and cipher sensitivity analysis show that the encryption scheme has a better security. Compared with traditional encryption scheme and one-dimensional logistic chaotic map, the new image encryption scheme has a better performance in speed, complexity, and security. This paper illustrates how to solve the problem of short periods and low precision of one-dimensional chaotic function by perturbation and LFSR together.     

Behavior of surface flaws in reactor pressure vessels under thermal-shock loading conditions

A pressurized-water, nuclear-reactor pressure vessel can be subjected to a severe thermal shock in the event of a loss-of-coolant accident (LOCA). If at the time of the LOCA there is a crack-like defect on the inner surface of the vessel, the crack may propagate as a result of the thermal shock. This paper discusses the conditions necessary for crack propagation during a LOCA, the detailed behavior of the cracks under these specific conditions, and an experimental program designed to determine the validity of the method of analysis (linear-elastic fracture mechanics) used to predict the behavior of flaws under severe thermal-shock loading conditions. A detailed fracture-mechanics analysis of the LOCA thermal shock was performed to help establish the scope of the experimental program. The results of this analysis indicate that present-generation and future PWR vessels will not experience excessive crack propagation. This is also true of earlier PWR vessels, which contain rather high concentrations of copper and, thus, are more susceptible to radiation damage, provided a phenomenon referred to as warm prestressing is effective. Eventually, the experimental program will include investigations of all the major fracture-mechanics phenomena predicted to occur under adverse LOCA-ECC conditions. Two of the experiments conducted thus far were designed for the study of long axial flaws that would penetrate no more than 20 percent of the wall of thick-wall steel test cylinders (533-mm OD×146-mm wall×914-mm length). During one of these experiments, no fast fracture took place, as predicted using LEFM. In the other experiment crack initiation and arrest were expected and took place, with a total penetration of ～16 percent. The agreement between experimental results and the LEFM analysis was very good, indicating that the LEFM analysis is valid at least for shallow flaws in thick-wall steel cylinders subjected to severe thermal shock.     

Investigation of the length and wave structure of the gas-dynamic section in straight and spreading gas jets

The results are given of an experimental investigation of the wave structure of straight and spreading gas jets. Dependences are obtained for the calculation of the length of the gas-dynamic part of straight and spreading gas jets.     

Multi-scale Measurement of (Amorphous) Polymer Deformation: Simultaneous X-ray Scattering,Digital Image Correlation and In-situ Loading

This paper presents a method to investigate the behaviour of polymers on different scales during deformation using simultaneously collected synchrotron X-ray scattering, digital image correlation (DIC) and tensile loading. The method is demonstrated through experiments made on specimens of amorphous polycarbonate. Deformation is measured in-situ, simultaneously across different scales from the macroscopic deformation, measured using sensors on the tensile machine, to the full-field mesoscopic deformation, measured using DIC, down to the deformation of the nano-scale structure, studied using small and wide angle X-ray scattering (SAXS/WAXS). The DIC reveals highly inhomogeneous deformations that render conventional techniques for measuring deformation, such as extensiometers, virtually useless. The X-ray scattering is measured in several spatial points during continuous loading giving the evolution of the microstructure with respect to both spatial location and load level. The spatial mapping of the scattering reveals characters that would not be observed when only measuring at the centre point or measuring on a large area of the specimen, e.g. wide beam SAXS/WAXS or small angle neutron scattering (SANS). With these data, the macroscopic and the mesoscopic deformation can be correlated to the behaviour of the microstructure providing relevant information when developing micro-mechanical based constitutive models. The experimental results shown here indicate a direct correlation between the major principal strain direction and the maximum anisotropy direction of the SAXS patterns. The current approach can be extended to any kind of polymeric materials or polymer-based nano-composites.     

An electromagnetic shear-stress gage for large-amplitude shear waves

In many materials, especially plastics, ceramics and rocks, large-amplitude shear-wave propagation studies could provide valuable information for the development of constitutive equations. A newly developed electromagnetic-gage configuration provides an output voltage which is directly related to the dynamic shear stress in the material. The electromagnetic shear-stress gage has been used to make direct measurements of shear-wave stresses in PMMA and Solenhofen limestone. Large-amplitude shear waves were obtained with a new plate-impact technique which generates shear waves by a controlled-reflection process. The configuration of the stress gage permits it to be used simultaneously with more conventional electromagnetic velocity gages, thus providing both types of data in one experiment.     

Measurement of strain fields near coldworked holes

Residual strains near coldworked holes were measured for several degrees of radial expansion. Moiré-grating photography created magnified replicas of deformed gratings. Fringe patterns with sensitivity multiplication and S/N improvement were obtained by optical data processing and by using slotted apertures for photography. Computer data reduction and plotting provided the required strain maps.