Dynamic Torsion Research Articles

On repeated adiabatic shear band formation during high-speed machining1

Abstract We compare the repeated adiabatic shear band formation that takes place at sufficiently large cutting speeds in a number of materials during high-speed machining operations with the more well-known formation of a single shear band that often takes place at sufficiently large strain rates in dynamic torsion tests on these materials. We show that there are several major differences in the physics of the two deformation processes. In particular, the shear stress in machining over the tool-material contact length is not even approximately homogeneous. Additionally, in high-speed machining, the material flow can become convection-dominated, so that the tool can “outrun” the thermal front generated in the workpiece material by the high-strain-rate cutting process. We demonstrate by means of a one-dimensional continuum model that these differences can lead to repeated oscillations in the plastic flow of the workpiece material during high-speed machining, leading to the repeated formation of adiabatic shear bands.

High energy radiation cure of resin systems for structural adhesives and composite applications

Radiation cure polymerisation of a commercial diglycidyl ether of bisphenol F epoxy resin has been achieved using a 60Co irradiation source, compounding the monomer with few percentage of an onium salt catalyst. The cure process has been monitored by a gamma-calorimetric technique and systems irradiated at doses corresponding to different positions in the gamma-calorimetric curve have been characterised via solubility tests and dynamic mechanical torsion analysis. Changes in both the measured gel fractions and tan δ values were associated with the progress of polymerisation and crosslinking reactions and these were dose dependent. Furthermore, systems irradiated at lower doses exhibited a latent thermal reactivity, undergoing further crosslinking by high temperature treatments, thus suggesting that synergy by the combination of radiation and thermal cure can help to achieve the desired applicative properties of these systems. These results have been discussed in the light of the most accredited radiation-induced polymerisation mechanisms for epoxy resins.

Rheological behavior of cellulose/monohydrate of N-methylmorpholine N-oxide solutions. Part 2. Glass transition domain

Dynamic mechanical experiments performed with original conditions allowed the analysis of a solution containing 15% cellulose dissolved in a monohydrate of N-methylmorpholine N-oxide (NMMO) in the amorphous state. The glass transition zone is studied by dynamic tensile experiments, while dynamic torsion technique is used to determine the viscoelastic behavior in the glassy state. A master curve of the storage and loss modulus versus frequency can be deduced from the isochronal curves measured by both techniques. This work allows one to complete the corresponding master curve obtained for the ‘liquid’ state and presented in a previous work [Rheol. Acta 1998;37: 107]. The measurements below the glass transition temperature exhibit two secondary relaxations. A modeling of the overall viscoelastic behavior, using the Nowick and Berry approach and the quasi-point defect theory, is proposed. Physical parameters deduced from this modeling are then discussed.

Dynamic deformation behavior of an oxide-dispersed tungsten heavy alloy fabricated by mechanical alloying

The objective of this study is to investigate the dynamic deformation and fracture behavior of an oxide-dispersed (OD) tungsten heavy alloy fabricated by mechanical alloying (MA). The tungsten alloy was processed by adding 0.1 wt pct Y2O3 powders during MA, in order to form fine oxides at triple junctions of tungsten particles or at tungsten/matrix interfaces. Dynamic torsion tests were conducted for this alloy, and the test data were compared with those of a conventional liquid-phase sintered (LPS) specimen. A refinement in tungsten particle size could be obtained after MA and multistep heat treatment without an increase in the interfacial area fraction between tungsten particles. The dynamic test results indicated that interfacial debonding between tungsten particles occurred over broad deformed areas in this alloy, suggesting the possibility of adiabatic shear-band formation. Also, oxide dispersion was effective in promoting interfacial debonding, since the fine oxides acted as initiation sites for interfacial debonding. These findings suggest that the idea of forming fine oxides would be useful for improving self-sharpening and penetration performance in tungsten heavy alloys.

Upward modulus trend in NiAl and NiFeAl single crystals

Dynamic Young modulus, torsion modulus and elastic energy dissipation were measured in Ni 56.2Fe 0.3Al 43.1Ta 0.3Mo 0.1 (NiAl crystal) and Ni 56.6Fe 12.3Al 30.2Hf 0.6(Al 2O 3) 0.3 (NiFeAl crystal). The elastic constant C′=( C 11− C 12)/2 has in both alloys a positive temperature derivative: (d C′/d T)>0 from 150 K up to 1300 K. The elastic energy dissipation exhibits a Debye-like peak whose activation energy is 2.36±0.05 eV in NiAl and 1.98±0.09 eV in NiFeAl. The peak is described as a Zener’s pair reorientation.

The Impact of a Sphere on a Timoshenko Thin-Walled Beam of Open Section With due Account for Middle Surface Extension

The problem on the normal impact of an elastic sphere upon an elastic Timoshenko arbitrary cross section thin-walled beam of open section is considered. The process of impact is accompanied by the dynamic flexure and torsion of the beam, resulting in the propagation of plane flexural-warping and torsional-shear waves of strong discontinuity along the beam axis. In addition, the process of impact is accompanied by large transverse deformations and large deflection of the beam in the place of impact, with the consequent generation of longitudinal shock waves and large membrane contractive (tensile) forces. Behind the wave fronts up to the boundaries of the contact region (the beam part with the contact spot), the solution is constructed in terms of one-term ray expansions. During the impact, the sphere moves under the action of the contact force which is determined due to the Hertz’s theory, but the contact region moves under the attraction of the contact force, as well as the twisting and bending-torsional moments and transverse and membrane forces, which are applied to the lateral surfaces of the contact region. Simultaneous consideration of the equations of sphere and the contact region motion leads to the Abel equation of the second kind, wherein the value characterizing the sphere and beam drawing together and the rate of change of this value are used as the independent variable and the function, respectively. The solution to the Abel equation written in the form of a series allows one to determine all characteristics of the shock interaction of the sphere and beam.

DYNAMIC BENDING AND TORSION STIFFNESS DERIVATION FROM MODAL CURVATURES AND TORSION RATES

In order to maintain the reliability of civil engineering structures, considerable effort is currently spent on developing a non-destructive vibration testing method for monitoring the structural integrity of constructions. The technique must be able to observe damage, secondly to localize the damage; and finally to give an idea of the severity of the damage. Within the framework of relating changes of measured modal parameters to changes in the integrity of the structure, it is important to be able to determine the dynamic stiffness in each section of the structure from measured modal characteristics.A damaged structure results in a dynamic stiffness reduction of the cracked sections. The dynamic stiffnesses provide directly an indication of the extension of the cracked zones in the structure. The dynamic stiffness reduction can also be associated with a degree of cracking in a particular zone.In an experimental programme, a concrete beam of 6 m length is subjected to an increasing static load to produce cracks. After each static perload, the beam is tested dynamically in a free–free set-up. The change in modal parameters is then related to damage in the beam.The technique that will be presented in the paper to predict the damage location and intensity is a direct stiffness derivation from measured modal displacement derivatives. Using the bending modes, the dynamic bending stiffness can be derived from modal curvatures. Using the torsional modes, the dynamic torsion stiffness can be derived from modal torsion rates.

Non-uniform and dynamic torsion of elastic beams Part 2: The double torsion test

Part 1 of this paper developed a one-dimensional fourth-order partial differential equation for dynamical torsion of rectangular beams. It was then validated against static and dynamic test cases. This concluding part applies the equation to the double torsion fracture test, in which a crack propagates along the plane joining two adjacent torsion beams as they are twisted in opposite senses. The resulting model is extensively validated against experimental and finite element results. It is then used to explain the shape of the curved crack front which is characteristic of this test.

Non-uniform and dynamic torsion of elastic beams Part 1: Governing equations and particular solutions

The double torsion fracture test has been widely used in the past for measuring resistance to crack growth under static loading and, more recently, under high-loading-rate conditions. Specimen deformation in this test is conventionally analysed on the basis of a one-dimensional torsion equation. Under dynamic conditions, it is imperative to establish an accurate torsion equation which can be used to model the double torsion test. The present paper describes the development, in this context, of a dynamic fourth-order partial differential equation for one-dimensional torsion, based on Barr's equation. The equation obtained in this paper accounts for the axial inertia associated with cross-sectional warping and the axial stresses which arise when warping is constrained. The equation can also accommodate non-linear elasticity. The equation is validated, using Barr's own data, for the torsional resonance problem which he studied and, using finite-element analysis, for a problem of constrained static torsion analysed by Timoshenko.

The dynamic properties of a pumiceous sand

The seismic site response analysis of sand deposits requires an understanding of the dynamic properties of the soils involved. Most dynamic soil data available in the literature has been derived for sands which do not contain pumice. Consequently, the relevance of this data to the behaviour of pumice sands is unclear. An extensive experimental investigation of the dynamic response of a pumice sand was therefore undertaken. The liquefaction response obtained from cyclic triaxial tests, and the shear modulus variation with strain amplitude observed in bender element and dynamic torsion tests were examined. The cyclic triaxial test results indicated that the liquefaction response was similar to that observed for quartz sands. However, the low strain shear modulus of the pumice sand was found to be significantly less than that of quartz sands at similar relative densities, and the nonlinear stress-strain behaviour was markedly different from that of other sands, particularly in the mid strain range.

Characterization of unidirectional carbon fibre reinforced plastic laminates

The purpose of the present paper is to outline a set of recommended tests in order to characterize the behavior of carbon fibre reinforced plastic laminates. The tests outlined in this contribution are classification of visual defects, dimension and density, fibre and resin content, tensible strength, apparent interlaminar shear strength, in-plane shear modulus, dynamic torsion property, static bending property, dynamic bending property, and thermal expansion coefficient. As a selected example, results of two tensile tests on CFRP laminates are reported.

Covariant quantization of the Volovich-Katanaev model

The Volovich-Katanaev model of two-dimensional gravity with dynamic torsion is considered in terms of the Batalin-Vilkovysky quantization and in the framework of the background field method.

The rate-dependent deformation and localization of fully dense and porous Ti-6Al-4V

The rate-dependent deformations of the titanium alloy Ti-6A1-4V are investigated using a combination of standard testing machines and compression and torsional Kolsky bars. Both homogeneous and localized deformations of both non-porous (‘fully dense’) and porous (7.6% porosity) versions of the alloy are studied. The microstructures of the two materials were made similar through heat-treatment, with the primary difference being the presence of the porosity. The fully dense Ti-6Al-4V (for this Widmänstatten microstructure) is found to show negligible strain hardening in compression (either quasistatic or dynamic), while the porous Ti-6Al-4V shows significant strain hardening in compression (both quasistatic and dynamic). The difference is believed to be because of the progressive compaction of the pores with increasing compressive strain. Both the fully dense and porous Ti-6Al-4V are observed to be rate-sensitive, with an increase in flow stress of ~ 30% over a six decade increase in strain rate. The strength-reduction due to porosity is ~ 20% for both quasistatic and dynamic strain rates. The constitutive response of the fully dense Ti-6Al-4V alloy in torsion is consistent with data in the literature, and again shows negligible strain hardening. The porous Ti-6Al-4V also shows negligible strain hardening in torsion, in contrast with the strong hardening evident in the compression data. This influence of the stress state on the behavior of the porous metal is due to the sensitivity of the pores to the mean (hydrostatic) stress. Specimens of the fully dense Ti-6Al-4V develop a deformation instability (during compression) in the form of a localized shearing failure in a plane at about 45° to the compression axis. The localized shearing failure in the fully dense metal consists of ‘deformed’ shear bands 3–10 μm in width which develop after a critical strain of 8–10%. In contrast, the porous Ti-6Al-4V specimens never fail in compression, showing homogeneous deformation even up to 30% strain. The relative stability of the porous metal is believed to be a result of the hardening mechanism afforded by the progressive compaction of the pores with increasing compressive strain. Shear bands are developed in both the fully dense and porous Ti-6Al-4V alloys after dynamic torsion. The critical shear strains to failure are ~ 14% for the fully dense metal and ~ 7% for the porous metal. Thus, the presence of the porosity destabilizes the deformation in shearing, but appears to stabilize the deformation in compression.

Some Poincaré gauge theory Lagrangians with well-posed initial value problems

Two four-parameter subclasses of the Poincaré gauge theory of gravity with dynamic torsion are shown to have a well-posed initial value problem. Each describes, in addition to the usual spin 2 massless graviton, one extra spin 0 dynamic torsion mode. These classes are counterexamples to certain recent claims.

Investigation on Ceramic–Metal Joints for Shaft–Hub Connections in Gas Turbines

This paper shows possibilities for joining ceramic rotors to metal shafts. The investigations presented include exemplary joining methods for shaft–hub connections for ceramic rotors in gas turbines, as positive, permanent locking, or a combination of both. Active brazing as well as the combination of brazing or adhesive bonding and positive locking are discussed. Different shaft–hub connections were tested. The results of experimental investigations as static shear, bending, and torsion tests as well as dynamic torsion tests will be presented. In addition to the experimental investigations, finite-element analyses were made. Elastic calculations on simple geometries have shown the influence of different parameters like the thermal coefficients and the geometry at the joint face. Calculations were done to reduce the induced tensile stress in the joint and to increase carrying capacity. The calculations were also transferred to the shaft–hub connections to optimize the geometry of the joint faces.

Investigation of wave processes in a Timoshenko thin-walled beam of open section caused by the shock subjection of an elastic sphere upon its surface.

The problem on the normal impact of an elastic sphere upon an elastic Timoshenko beam of thin-walled monosymmetrical open section is considered. The process of impact is accompanied by the dynamic flexure and torsion of the beam, resulting in the propagation of plane flexural, shear, and torsional waves of strong discontinuity along the beam axis. Behind the wavefronts the solution is constructed in terms of one-term ray expansions. During the impact the sphere moves under the action of the contact force which is determined due to the Hertz’s theory, but the contact region moves under the action of the contact force, and the bending-torsional moment and transverse forces, which are subjected to the lateral surfaces of the contact region and are determined using one-term ray expansions. The joint consideration of the equations of sphere and the contact region motion leads to the Abel equation of second kind in the rate of change of the value of the sphere and beam drawing together. The solution to the Abel equation written in the form of a series in terms of this value allows one to determine all characteristics of the sphere and beam shock interaction.

Tool for dynamic analysis of concrete box tubes subjected to torsion

A microcomputer-based software system DSBT (dynamic solver for reinforced concrete box tubes) is developed. The program is coded in C and can be conveniently executed on a personal computer. The theoretical background for this program includes three parts: (1) the truss model theory for the primary curves of box tubes, (2) the analytical model of the hysteresis loops, which describes the behavior of the box tubes under repeated loading and unloading, and (3) the dynamic model used for dynamic analysis. The combination and implementation of these three components forms a useful tool for the dynamic analysis of such box tubes. Using this tool, three examples are analyzed: a box tube under static torsion, a one-storey box tube and an eight-storey box tube subjected to dynamic torsion.

Vibration and flutter of stiff-inplane elastically tailored composite rotor blades

Aeroelastic response, blade and hub loads, and shaft-fixed aeroelastic stability is investigated for a helicopter with elastically tailored stiff-inplane composite rotor blades. A free wake model for nonuniform rotor inflow is integrated with a recently developed finite-element-based aeroelastic analysis for helicopters with tailored composite blades. Pitch-flap and pitch-lag elastic couplings, introduced through the anisotropy of the plies in the blade spar, have a significant effect on the dynamic elastic torsion response. Positive and negative pitch-flap couplings reduce vertical hub shear forces approximately 20% in the high vibration transition flight regime, however, negative pitch-flap elastic coupling significantly increases inplane hub shear forces at all flight speeds. The influence of pitch-flap, pitch-lag, and extension-torsion elastic couplings on the rotating frame blade bending moments is small. Ply-induced composite couplings have a powerful effect on blade stability in both hover and forward flight. Positive pitch-flap, positive pitch-lag, and positive extension-torsion couplings each have a stabilizing effect on lag mode damping. Negative pitch-lag coupling has a strong destabilizing effect on blade lag stability, resulting in a mild instability at moderate flight speeds.

The solution of dynamic Point-Ring-Couple in an elastic space and its properties

The solution of dynamic Point-Ring-Couple at the origin, on z=0 plane, in an elastic space is presented and its properties are discussed. Let shocking loads be uniformly distributed, along the direction of circumference at a circle, on z=0 plane, with radius a and centered at the origin. Then, the solution of our problem is obtained via integral calculation for a→0. When the intensity of this dynamic Point-Ring-Couple is varied with sinωt, the cones in the elastic space with apex at the origin and the z-axis be its symmetric axis, become zero stressed surfaces at any time instance. The solution of dynamic torsion problem of revolution solids with these cones as boundary under the application of torque varied with sin ωt is found.

Dynamic analysis of ocular torsion in parabolic flight using video-oculography

Dynamic ocular torsion was investigated in a group of healthy subjects during the course of parabolic flight by means of our video-based eye movement recording method—video-oculography. This technique enables a non-invasive dynamic measurement of all three dimensions of eye movement in a harsh experimental environment such as parabolic flight. The test subjects were positioned so that the changing resultant gravito-inertial field in the aircraft was aligned with their interaural ( y) axis, primarily stimulating the utricular organs. The analysis of the torsional component of eye movement during the change of gravity between 1.8-0 and 0–1.8 g demonstrated a static component—well known as the ocular counter roll—and a dynamic component, which leads to a slight overshoot in the torsional response. These static and dynamic component of ocular torsion correlate with previous neurophysiological findings.