High Modulus Materials Research Articles

Deformation of self-reinforced polymers in weak mechanical fields during heating

It is known that the self-ordering ability is a characteristic trait of polymers forming a liquid-crystal phase. The processes of self-orientation of mesomorphic polymers in the liquid state are due to factors such as concentration of the solution or the temperature of the melt. In solid polymers the same role may be played by the temperature and the level of deformation (in a loaded specimen). It was shown in (1) that when some critical deformation is attained, it leads to the formation of structures with high thermal stability in polyamides (PA) obtained from a lyotropic solution, and in thermotropic polyester. Improved thermal stability manifests itself during extension, a consequence of which is also increased rigidity of the material and its self-reinforcement in the mechanical field. In our present work we obtained results enabling us to characterize processes of spontaneous deformation of aromatic PA both along the axis of orientation and transversely. The cause of deformation is the effect of a thermal field, and weak mechanical fields are used solely for fixing the specimen in a certain position; there the small loads applied to high-modulus materials barely bring about their deformation. In our work we chose infrared (IR) spectroscopy as directmore » method of investigating structural changes in spontaneous deformation. In distinction to x-ray structure analysis IR spectroscopy yields more complete information on the orientation of the crystalline as well as of the amorphous phase of polymers, and also on the molecular mobility.« less

Fiber-reinforced-superconductors with high-elastic modulus and low thermal prestrain on Nb/sub 3/Sn layers for high-field pulsed magnet

We have been developing a new type of Nb/sub 3/Sn superconductor, a fiber-reinforced-superconductor (FRS), to make an attempt at the application of high-field pulsed superconducting magnets. FRSs have high elastic modulus fibers such as tungsten so that the strain on superconducting layer caused by hoop stress can be reduced. Such high elastic modulus materials however, tend to have lower thermal expansion coefficient compared with Nb/sub 3/Sn. The resultant tensile prestrain on Nb/sub 3/Sn at liquid helium temperature brings about the degradation of superconducting characteristics. In this paper, it is shown that the strain characteristics of FRS can be largely improved by adopting a tungsten alloy, keeping high elastic modulus of pure tungsten.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Generalized Method For The Optimal Design Of Beams Under Flexural Vibration

A generalized method is developed for the design of a cantilever of circular cross-section in flexural vibration. The dynamic rigidity of the overhang bar can be increased if the root portion of the bar is made of high elastic modulus material while the free end portion is composed of low density material. Hence, the method developed is for a beam composed of two materials at different ends, but the method applies to a beam of a single material as well. The variational statement is written, and a set of non-linear boundary value equations are obtained. By solving these equations, the shape of the bar and the material length ratio (length of the material at root portion over total overhang length) which would result in a highest first mode natural frequency is determined. The optimal shape, material length ratio and flexural rigidity of the overhang bar composed of two materials under various constraints are discussed.

Hybrid Nanocomposite Materials—between inorganic glasses and organic polymers

AbstractThe sol–gel process, with its associated mild conditions, offers a new approach to the synthesis of composite materials with domain sizes approaching the molecular level. Transparent organic–inorganic composites can be prepared by dissolving preformed polymers into sot–gel precursor solutions, and then allowing the tetraalkyl orthosilicates to hydrolyze and condense to form glassy SiO2 phases of different morphological structures. Alternatively, both the organic and inorganic phases can be simultaneously formed through the synchronous polymerization of the organic monomer and the sol–gel precursors. Depending upon such factors as the structures of the organic and inorganic components, the phase morphology, the degree of interpenetration, and the presence of covalent bonds between the phases, the properties of these composites can vary greatly and range from elastomeric rubbers to high–modulus materials.

Analytical stress intensity solution for the stable Poisson loaded specimen

An analytical calibration of the Stable Poisson Loaded (SPL) specimen is presented. The specimen configuration is similar to the ASTM E-561 compact-tension specimen with displacement controlled wedge loading used for R-curve determination. The crack mouth opening displacements (CMOD's) are produced by the diametral expansion of an axially compressed cylindrical pin located in the wake of a machined notch. Due to the unusual loading configuration, a three-dimensional finite element analysis was performed with gap elements simulating the contact between the pin and specimen. In this report, stress intensity factors, CMOD's, and crack displacement profiles, are reported for different crack lengths and different contacting conditions. It was concluded that the computed stress intensity factor decreases sharply with increasing crack length thus making the SPL specimen configuration attractive for fracture testing of brittle, high modulus materials.

On the tensile testing of high modulus polymers and the compliance correction

AbstractThe application of a method to determine and correct for the influence of non‐specimen extension in tensile testing is reviewed and demonstrated using two different thermotropic liquid crystalline polymers. In the tensile testing of high modulus polymer extrudate, where the amount of specimen extension is inferred from the crosshead travel, the error associated with system compliance can be significant and parameters such as modulus and elongation will be in error. The need to apply the correction depends on the magnitude of the product of the sample modulus and cross‐sectional area, divided by the test gage length, relative to the system compliance value. Its application is not necessarily restricted to high modulus materials, and can be extended to samples of larger cross‐sectional area and lower modulus. Guidance to assist in the choice of a suitable gage length to avoid compliance correction and a method to quantify the error contribution is presented.

Enhancement of dynamic stability of cantilever tooling structures

The least rigid components of machining systems are cantilever tools and cantilever structural units of machine tools (rams, spindle sleeves, etc.). These components limit machining regimes due to the development of chatter vibrations, limit tool life due to extensive wear of cutting inserts, and limit geometric accuracy due to large deflections under cutting forces. Use of high Young's modulus materials (such as sintered carbides) to enhance the dynamic quality of cantilever components has only a limited effect and is very expensive. This paper describes a systems approach to the development of cantilever tooling structures (using the example of boring bars) which combine exceptionally high dynamic stability and performance characteristics with cost effectiveness. Resultant success was due to: (1) a thorough survey of the state of the art; (2) creating a “combination structure” concept with rigid (e.g. sintered carbide) root segments combined with light (e.g. aluminum) overhang segments, thus retaining high stiffness and at the same time achieving low effective mass (thus, high mass ratios for dynamic vibration absorbers, or DVAs) and high natural frequencies; (3) using the concept of “saturation of contact deformations” for efficient joining of constituent parts with minimum processing requirements; (4) suggesting optimized tuning of DVAs for machining process requirements; (5) development of DVAs with the possibility of broad-range tuning; (6) structural optimization of the system; and (7) using a novel concept of a “Torsional Compliant Head”, or TCH, which enhances dynamic stability at high cutting speeds and is suitable for high rev/min applications since it does not disturb balancing conditions. The optimal performance and interaction of these concepts were determined analytically, and then the analytical results were validated by extensive cutting tests with both stationary and rotating boring bars, machining steel and aluminum parts. Stable performance with length-to-diameter ratios up to L/ D = 15 was demonstrated, with surface finish 20–30 μm with both steel and aluminum at L/ D = 7–11. Comparative tests with commercially available bars demonstrated the advantages of our system.

Tensile failure load and fiber diameter as stochastic variables in the determination of fiber strength statistics

The combined effect of treating failure load and fiber diameter as stochastic variables, on reliability is examined. The approach assumes specific distributions for diameter and failure load to determine the reliability of the system, through a joint probability distribution function defined over a two-dimensional region of feasibility. It is shown that neglecting diameter variations results in a lower probability of failure making the prediction for the system potentially unsafe. This effect is significant for high Weibull modulus materials.

Field studies on dynamic properties of reinforced earth

The concept of reinforced earth has not become popular in the case of foundations for buildings. Presumably, the practical difficulties in application and the exorbitant cost have outweighed the beneficial aspects of ‘Reinforced Earth’ in such applications. Block foundations which are usually provided for machines to take care of the dynamic loads are small and compact and the improvement of the base with reinforcements should not be a difficult or impractical proposition. In this investigation, the feasibility of improving the dynamic properties of soil b ase by applying high modulus materials, such as steel wires and low modulus materials as geotextiles, and a combination of both have been studied in a standard forced vertical block resonance test. The feasibility and the supremacy of the ‘Reinforced Earth’ with the reinforced bases of (i) mild steel frame stiffened with high tensile wires (ii) sand coated geotextiles with the inclusion of a thin layer of frictional sand and (iii) sand coated geotextiles stiffened with welded mesh, have been brought out.

Fracture Toughness of Nuclear Graphites

Nuclear graphite materials behave as a brittle material during their fracture, so that, properties of higher fracture toughness and crack extension resistance have been required for graphites. The knowledge of fracture behavior of graphites must be needed for its modification, however, those behavior of graphites has not been examined in detail considering to its mechanical and physical properties.In this paper, fracture toughness tests were performed for nuclear graphites and properties of fracture toughness and crack extension resistance of graphites were examined as a function of mechanical and physical properties of graphites. From the results, the following conclusions were derived:(1) 3-point strength of graphites increases as Young's modulus increases.(2) Relationship between density and Jic was not found.(3) Jic increases as Young's modulus increases for lower Young's modulus materials, however, for high Young's modulus materials, Jic decreases as Young's modulus increases.(4) The graphites consisted of larger grain have larger crack extension resistance.(5) The value of JICE/π σsb2 is related to mean grain size of graphites, where E and σsb were Young's modulus and 3-point bending strength respectively.

Design &amp; fabrication of an advanced, lightweight, high stiffness, railgun barrel concept

The integrated thermal, electrical, and structural (static and dynamic) analysis performed on several candidate barrel configurations have led to an electromagnetic launcher (EML) design that satisfies the ARDEC (US Army Armament Research, Development, and Engineering Center)/DARPA (Defense Advanced Research Projects Agency) design goals. An advanced lightweight, high-stiffness, easily maintained, 9-15 MJ launcher has been designed, and its fabrication is nearing completion. A 1 m prototype using all the full-scale components, except for a shorter barrel length, is currently under test validation. The design features of the barrel show that utilization of high modulus materials, application of optimal barrel geometry, and application of active prestressing provides a barrel with high stiffness and utility. >

Special features of the electron structure of ultradisperse powders of cubic boron nitride

ing factors. The quantum dimensional effect determined by the absence of the long-range order in the volume of the particle leads to extensive changes in the EES in comparison with the thick material, especially to a reduction of the width of the valency band and appearance of new energy states forbidden in the thick materials [2]. The electrons with the sp-symmetry are more sensitive to the dimensional effect than the electrons of the d-symmetry, and the structure of the EES of the small particles simulates to a certain degree the EES of the surface of the thick crystal. However, these effects are detected at particle sizes smaller than i0 nm. The second factor is a reduction of the interatom spacing and deformation of the crystal lattice in small particles under the effect of surface tension which may cause corresponding deformation of the EES [4]. The third factor is a high Laplace pressure inside the small particles. For high-modulus materials with a higher surface energy (such as, for example, diamond, dense modifications of BN, refractory carbides and nitrides) with particles of 0.i ~m this pressure exeeds 1GPa and can cause barich changes in the EES [4, 5]. The final factor is an increase of the relative contribution on the free surface to the overall pattern of the EES of the material with a reduction of the particle size. It is well-known that the EES on the surface reflects the states of structural vacancies and is characterized by the presence of high-density nonbonding states in the area of the ceiling of the valency zone [6, 7]. As a result of theseEES changes, the material in the ultradispersed state assumes special physicochemical properties [2], especially lower sintering temperatures and higher sintering rates [i, 8], and a high catalytic activity. The most informative methods of experimental examination of the EES of the surface in the thick crystals are electron spectroscopy with angular resolution and electron Auger spectroscopy. However, for materials in the ultradisperse state it is more efficient to use ultrafine x-ray spectroscopy (with a slightly greater depth of excitation of the spectrum) because the efficient cleaning of the surface of a set of ultradisperse particles to remove adsorbed impurities associated with considerable difficulties and the surface state provides a relatively large contribution to the total spectrum of the valency bands of the materials. In [3] this method was used successfully for examining the EES of the UDP of a monoatomic refractory material (diamond). The EES in the ultradispersed polyatomic chemical compounds has not as yet been studied by the spectral methods. In this work, the method of ultrafine x ray emission spectroscopy based on K-bands of boron and nitrogen was used to examine the EES in the populated part of the valency band of the UDP of cubic boron nitride of the El'bor grade. The powders were synthesized from hexagonal BN with a graphite-like structure in industrial high-pressure systems; magnesium diboride was used as a catalyst/solvent [9]. The BNcu b crystals were separated from the rem

Determination of the stress intensity factor by methods of photoelastic simulation

Various methods of determination of stress intensity factors from the patterns of the isochromes, the isopachs, and the absolute differences in shape at the tip of a notch are analyzed. The range of extrapolation of the values of KI within which the theoretically obtained stress distributions coincide with the stresses measured experimentally on a model with a finite radius of the stress raiser tip is established. Determination of the parameter KI from the patterns of absolute differences of the shape is significantly more complex than from the patterns of the isochromes and isopachs but is justified on models of a high-modulus material when increased accuracy, reliability of the results, and an analysis of the stressed and strained state of a specimen with separation of the main stresses are necessary.

High-performance materials from gel-like spherulites of ultra-high-molecular-weight polyethylene

A new method using gel-like spherulites will be presented for obtaining high-performance materials of ultra-high-molecular-weight polyethylene (UHMW-PE), which is available for the production of high-strength and high-modulus materials having a large cross-sectional area, for example, rods and thicker tapes. Such high-performance organic materials were not known until the development of this method in 1983. Ultra-drawability and characteristics of UHMW-PE produced by this method are discussed, based on the fine structure of gel press sheet.

Preparation of thick stress-free molybdenum films for a resistively heated ion source

In order to deposit thick, adherent and crack-free thick films of high modulus materials it is necessary for the deposited material to be stress free. In this paper we describe the use of a pressure cycling technique in a post cathode magnetron sputtering system for depositing thick (5 μm) stress-free films of molybdenum. The pressure cycling technique utilizes the fact that sputter-deposited materials typically have high tensile stresses when deposited at high sputtering gas pressures and high compressive stresses when deposited at low gas pressures. By cycling the pressure from the high pressure regime to the low pressure regime during deposition nearly stress-free films can be deposited. The film thickness distribution in the post cathode magnetron sputtering configuration can be changed by varying the magnetic field conditions. The electrical resistivity and thermal coefficient of resistivity of the deposited films are functions of the substrate surface condition and the magnetic field conditions during sputter deposition.

Nonlinear bending and vibration of symmetrically laminated orthotropic elliptical plate with simply supported edge

This paper deals with the static large deflection and the large amplitude free flexural vibration of a symmetrically laminated orthotropic elliptical plate with a simply supported immovable edge. A unified approximate solution of the dynamic von Karman-type equations of the plate in terms of the deflection and two inplane displacements is presented by use of a modified Galerkin procedure. Two inplane equations of equilibrium and the associated inplane boundary conditions are satisfied exactly. Numerical computations are performed for static and dynamic responses of homogeneous and symmetric cross-ply elliptical plates with different axes ratios, numbers of layers and high-modulus material properties. In the static and dynamic linear cases, present results are compared with available data.

Microstructural evaluation of rapidly solidified Al-Li-Be alloys

Aluminium-lithium-beryllium alloys are a group of low-density, high-modulus materials that potentially have technological importance in aerospace structures. In this paper, a series of such alloys has been produced using rapid solidification processing via melt spinning. The microstructures of the alloys have been investigated in the as-melt-spun condition, after consolidation and heat treatment to peak hardness, and after tensile testing in the heat-treated condition. In particular, changes in the size and distribution of primary beryllium particles and Al3Li precipitates are described after consolidation and processing. The mechanical properties of the alloys in the heat-treated condition are also presented.

Studies on the Transient Shear Flow Behavior of Liquid Crystalline Polymers

An understanding of the flow behavior of liquid crystalline polymers (LCP's) is of immense practical value because of the potential to form high modulus materials from these polymers. These fluids exhibit a high degree of structure even in the quiescent state, as evidenced by their ability to transmit polarized light. In an effort to understand how the structure changes during flow, we have carried out a study on the transient shear flow properties of two thermotropic copolyesters of 60‐ and 80‐mole % para‐hydroxybenzoic acid (PHB) and polyethyleneterephthalate (PET) and a lyotropic system of poly‐p‐phenyleneterephthalamide (PPT) in 100% sulfuric acid. In one of the first theories concerned with the flow behavior of liquid crystalline fluids, which was proposed by Ericksen, the transient flow properties are all predicted to be due to changes in orientation of a director which describes the orientation of packets of rod‐like molecules. Stress growth, interrupted stress growth, and stress relaxation experiments are carried out on the three LCP's and at first sight are in qualitative agreement with the predictions of Ericksen's theory. However, wide angle X‐ray scattering analysis of quenched samples subjected to shear flow along with annealing experiments on oriented samples indicate that these materials do not orient readily in shear flow. Furthermore, orientation generated during extensional flow relaxes at a rate much faster than is indicated by the interrupted stress growth experiments. It is concluded that the stress growth response of LCP's is due to a disruption of a domain structure which exists within the fluid rather than to orientation changes of the domains of rod‐like molecules.

The effect of double layer coatings of high modulus on contact stresses

Abstract In an earlier paper (Van der Zwaag and Field 1982), we investigated, using finite element methods, the effect of a thin, hard coating on the stress field generated by a spherical indenter on a uniform halfspace. Of particular practical interest was the reduction in the maximum (radial) tensile stresses in the substrate solid as the modulus and thickness of the coating increased. Experimental support for the theoretical predictions was given by Van der Zwaag and Field (1983). In the present paper, the investigation is extended to examine the potential of double layer coatings of two different high modulus materials. It is shown that a suitable selection of the properties of the two layers can reduce the tensile stresses in the substrate solid compared to the values in an uncoated substrate. Two particular systems are examined in detail. Potential benefits of monolayer and multilayer coatings are discussed critically. The results have application to a range of practical problems.

Study of the stress-strain state of three-layer conical shells with skins made of high-modulus composite materials

Study of the stress-strain state of three-layer conical shells with skins made of high-modulus composite materials