Showing papers on "Deformation (engineering) published in 1973"

The Physics of Glassy Polymers

Abstract: (The Nature of Polymer Glasses, Their Packing Density and Mechanical Behaviour).- The Nature of Polymeric Glasses.- The common glassy polymers.- The softening of polymer glasses.- Polymer melts and rubbers.- The crystallisation of polymers.- Amorphous isotactic polymers.- The morphology of amorphous polymers.- Packing Volume in the Glassy State.- The expansion volume of amorphous polymers.- Free volume concepts derived from viscosity theories.- Viscosity and free volume in polymers.- Geometrical factors affecting the possible value of the free volume at Tg.- Bernal's random close packed volume.- The Rigidity of Polymer Glasses.- Large Deformations and Fracture.- References.- 1 The Thermodynamics of the Glassy State.- 1.1 Introductory Thermodynamic Considerations.- 1.2 Glassy Solidification and Transition Phenomena.- 1.2.1 General considerations and transitions of different order.- 1.2.2 Glassy solidification with one or several internal parameters.- 1.2.3 Experimental results.- 1.2.4 Position of the equilibrium curve below the glass temperature.- 1.2.5 Zero point volume of a polymer.- 1.3 Results of the Thermodynamic Theory of Linear Relaxation Phenomena.- 1.4 Glassy Mixed Phases.- 1.4.1 The glassy solidification of polymer solutions.- 1.4.2 The glassy solidification of cross-linked systems. The coexistence of glassy phases with phases in internal equilibrium.- 1.5 The Mobility and Structure of Glassy Phases.- References.- 2 X-Ray Diffraction Studies of the Structure of Amorphous Polymers.- 2.1 Introduction.- 2.2 The Interaction of X-rays With Matter.- 2.2.1 Scattering by a free electron.- 2.2.2 Interference among scattered waves.- 2.2.3 Atomic scattering factor.- 2.2.4 Compton scattering.- 2.3 Order and Orientation in Polymers.- 2.3.1 Order.- 2.3.2 Orientation.- 2.4 Diffraction of X-rays by Amorphous Materials.- 2.5 Small Angle X-ray Scattering.- 2.5.1 Introduction.- 2.5.2 Experimental requirements for SAXS.- 2.5.3 Outline of the theory of SAXS.- 2.5.4 Some applications of SAXS.- 2.6 The Radial Distribution Function for Amorphous Polymers.- References.- 3 Relaxation Processes in Amorphous Polymers.- 3.1 Introduction.- 3.2 Molecular Motion in Polymeric Melts and Glasses.- 3.2.1 General description of relaxational processes.- 3.2.2 Relaxational processes at the crystal melt temperature.- 3.2.3 Relaxations in the amorphous state above Tg and below Tm.- 3.2.4 Relaxational processes at the glass transition.- 3.2.5 Relaxations in the glassy state.- 3.3 Secondary Relaxation Regions in Typical Organic Glasses.- 3.3.1 Secondary relaxation regions in Polyvinylchloride.- 3.3.2 Secondary relaxation regions in polystyrene.- 3.3.3 Secondary relaxations in polymethylmethacrylate.- References.- 4 Creep in Glassy Polymers.- 4.1 Introduction.- 4.2 Phenomenological Theory of Creep.- 4.2.1 Linear theory.- 4.2.2 Nonlinear theory-creep equations.- 4.2.3 Nonlinear theory-superposition rules.- 4.3 Apparatus and Experimental Methods.- 4.3.1 General principles.- 4.3.2 Special experimental requirements.- 4.3.3 Special experiments.- 4.4 Creep Phenomena in Glassy Polymers.- 4.4.1 Typical creep behaviour.- 4.4.2 Creep at elevated temperatures.- 4.4.3 Creep in anisotropic samples.- 4.4.4 Recovery behaviour.- 4.4.5 Creep under intermittent stress.- 4.4.6 Creep under abrupt changes of stress.- 4.5 Final Comments.- References and Bibliography.- 5 The Yield Behaviour of Glassy Polymers.- 5.1 Introduction.- 5.2 Exact Definitions.- 5.2.1 Stress.- 5.2.2 Strain.- 5.2.3 The deformation-rate tensor.- 5.2.4 The yield point.- 5.2.5 Nomenclature for deformation processes.- 5.3 Mechanical Tests.- 5.3.1 The tensile test.- 5.3.2 The uniaxial compression test.- 5.3.3 The plane strain compression test.- 5.3.4 Tests in simple shear.- 5.3.5 Machine elasticity.- 5.3.6 Drawing at constant load.- 5.4 Characteristics of the Yield Process.- 5.4.1 The yield point and the yield stress.- 5.4.2 The yield strain.- 5.4.3 Strain softening and orientation hardening.- 5.4.4 The strain-rate dependence of the yield stress.- 5.4.5 The temperature dependence of the yield stress and the yield strain.- 5.4.6 The effect of hydrostatic pressure on the yield stress and yield strain.- 5.4.7 The effect of polymer structure on the yield stress.- 5.4.8 Volume changes at yield.- 5.4.9 The Bauschinger effect.- 5.5 Inhomogeneous Deformation.- 5.5.1 The reasons for inhomogeneous deformation.- 5.5.2 The principle of maximum plastic resistance.- 5.5.3 The geometry of inhomogeneous deformation.- 5.5.4 Strain inhomogeneities in polymers.- 5.6 Structural Observations.- 5.6.1 Birefringence.- 5.6.2 Electron microscopy.- 5.7 Yield Criteria for Polymers.- 5.7.1 The Tresca yield criterion.- 5.7.2 The von Mises yield criterion.- 5.7.3 The Mohr-Coulomb yield criterion.- 5.7.4 The modified Tresca criterion.- 5.7.5 The modified von Mises criterion.- 5.7.6 Choice of a yield criterion for polymers.- 5.8 Molecular Theories of Yielding.- 5.8.1 Reduction of the Tg by the applied stress.- 5.8.2 Stress-induced increase in free volume.- 5.8.3 Break-down of entanglements under stress.- 5.8.4 The Eyring model.- 5.8.5 The Robertson model.- 5.8.6 The theoretical shear strength-Frank's modification of the Frenkel model.- 5.8.7 Disclinations.- References.- 6 The Post-Yield Behaviour of Amorphous Plastics.- 6.1 General.- 6.2 The Phenomena of' strain Softening'.- 6.2.1 Stress hardening.- 6.3 Plastic Instability Phenomena.- 6.3.1 Plastic instability in tension.- 6.3.2 Plastic instability in different stress fields.- 6.4 The Adiabatic Heating of Polymers Subject to Large Deformations.- 6.4.1 Reversible thermoelastic effect.- 6.4.2 Thermal effects in large plastic deformation.- 6.4.3 The experimental measurement of temperature changes during deformation.- 6.5 Orientation Hardening.- 6.5.1 Orientation hardening as a physical process.- 6.5.2 Factors affecting orientation hardening.- 6.5.3 A model for large polymer deformations.- 6.6 Large Deformation and Fracture.- 6.6.1 Crack propagation as a deformation process.- 6.6.2 Crazing as a plastic instability phenomenon.- 6.6.3 The growth of voids in a polymer glass.- 6.6.4 The nucleation of voids.- References.- 7 Cracking and Crazing in Polymeric Glasses.- 7.1 Introduction.- 7.2 Fracture Mechanics.- 7.2.1 Linear fracture mechanics.- 7.2.2 Measurements of KIC for glassy polymers.- 7.2.3 Crack-opening displacement.- 7.2.4 Energy balance approach.- 7.2.5 Measurements of surface work.- 7.2.6 Fracture stress.- 7.3 Fatigue Fracture.- 7.3.1 Fatigue failure by heat build-up.- 7.3.2 Fatigue crack propagation.- 7.4 Crazing.- 7.4.1 Crazing of glassy plastics in air.- 7.4.2 Environmental crazing.- 7.4.3 Theoretical aspects.- 7.5 Molecular Fracture.- 7.5.1 Kinetic theories of fracture.- 7.5.2 Experimental evidence for bond fracture.- 7.6 Conclusion.- References.- 8 Rubber ReinForced Thermoplastics.- 8.1 Introduction.- 8.2 Rubber Reinforced Glassy Polymers of Commercial Importance.- 8.2.1 Based on polystyrene.- 8.2.2 Based on styrene acrylonitrile copolymer (SAN).- 8.2.3 Based on Polyvinylchloride.- 8.3 Methods of Manufacture.- 8.3.1 Physical blending.- 8.3.2 Interpolymerisation process.- 8.3.3 Latex interpolymerisation.- 8.4 Incompatibility in Polymer Mixtures.- 8.5 Identification of Two Phase Rubber Reinforced Systems.- 8.6 Dispersed Phase Morphology.- 8.6.1 Toughened polystyrene.- 8.6.2 ABS copolymers.- 8.6.3 Polyvinylchloride.- 8.7 Optical Properties.- 8.7.1 Matching of the refractive index.- 8.7.2 Reduction in particle size.- 8.8 Mechanical Properties.- 8.8.1 Tensile properties.- 8.8.2 Dynamic mechanical properties.- 8.8.3 Impact properties.- 8.8.4 Structure-property relationships.- References.- 9 The Diffusion and Sorption of Gases and Vapours in Glassy Polymers.- 9.1 Introduction.- 9.2 Ideal and Non-ideal Sorption and Diffusion of Fixed Gases.- 9.2.1 Ideal diffusion and sorption of fixed gases.- 9.2.2 Non-ideal sorption and diffusion of fixed gases.- 9.3 The Effect of the Glass Transition on Gas and Vapour Diffusion in Polymers.- 9.4 Relaxation Controlled Transport and Related Crazing of Polymeric Glasses by Vapours.- 9.4.1 Introduction ..- 9.4.2 Relaxation controlled transport and solvent crazing.- 9.5 Some Effects of Crystallinity and Orientation on the Transport of Gases and Vapours in Glassy Polymers.- 9.5.1 Effect of crystallinity.- 9.5.2 The effect of orientation.- References.- 10 The Morphology of Regular Block Copolymers.- 10.1 Introduction.- 10.1.1 General.- 10.1.2 Microphase separation.- 10.2 Techniques Used for the Study of the Morphology of Block Copolymers.- 10.2.1 Low angle X-ray scattering.- 10.2.2 Electron microscopy.- 10.2.3 Other techniques.- 10.3 Variables Controlling the Morphology.- 10.3.1 Chemical variables.- 10.3.2 Physical variables.- 10.4 Studies with Specific Systems.- 10.4.1 Systems with liquid.- 10.4.2 The pure copolymers.- 10.5 Theories of the Morphology of Block Copolymers.- 10.5.1 Objectives.- 10.5.2 Principles of calculation.- 10.6 Implications of Theories and Comparison With Experiment.- 10.6.1 Influence of block molecular weight ratio.- 10.6.2 Effect of block molecular weights.- 10.6.3 Molecular orientation in the phases.- 10.6.4 Interfacial region.- 10.6.5 Effect of temperature on domain size.- 10.7 Mechanical Properties and Deformations.- 10.8 Crystallinity.- References.- Appendix I Glass Transition Temperatures and Expansion Coefficients for the Glass and Rubber States of some Typical Polymeric Glasses.- Appendix II Conversion Factors for SI Units.

The delamination theory of wear

Abstract: A new theory for wear of metals is considered. The theory is based on the behavior of dislocations at the surface, sub-surface crack and void formation, and subsequent joining of cracks by shear deformation of the surface. The proposed theory predicts qualitatively that the wear particle shape is likely to be thin flake-like sheets and that the surface layer can undergo large plastic deformation. It also predicts a number of experimentally observed phenomena such as the difference in wear particle sizes and the dependence of fretting wear rate on displacement amplitude. All theoretical predictions are supported by experimental evidences. A wear equation is developed based on the proposed theory.

Microstructures and Preferred Orientations of Experimentally Deformed Quartzites

Abstract: An experimental study of the plastic deformation of quartzite has produced microstructures and preferred orientations similar to those found in many natural rocks, and has identified the operative orienting mechanisms in most cases. The microstructures vary widely with conditions and presumably are related to the deformation mechanisms. Below 850°C at 10−5/sec (or 650°C at 10−7/sec), no recrystallization occurs; the deformation of the original grains is very inhomogeneous and deformation lamellae of many orientations are observed. At higher temperatures or slower strain rates, grain boundary recrystallization is present; the original grains are continuously flattened with increasing strain and only basal and prismatic deformation lamellae are observed. Above 800°C at 10−7/sec, recrystallization is complete after low strain. Below 800°C at 10−5/sec (or 600°C at 10−7/sec), a maximum of c axes develops parallel to the compression direction (σ1), while at higher temperatures and slower strain rates, a small-circle girdle of c axes develops about σ1. The opening half-angle of this girdle ranges from 20° to 45° and increases with increasing temperature and decreasing strain rate. Super-imposed on both of these c axis patterns is a tendency for the poles to positive trigonal forms, and the pole to the second order prism to be aligned parallel to σ1. The preferred orientations of the c axes and the prisms are consistent with external rotations produced by the observed intragranular glide. The difference in the preferred orientations of the positive and negative forms is due to mechanical Dauphine twinning. Strong evidence exists that these same orienting mechanisms have operated in many naturally deformed rocks.

The Principles of Engineering Materials

Abstract: 1. The Nature of Materials Science. 2. The Structure of Perfect Solids. 3. The Structure of Real Solids. 4. Equilibrium. 5. Kinetics. 6. Introduction to the Mechanical Properties of Solids. 7. Plastic Deformation in Crystalline Solids. 8. Strengthening Mechanisms. 9. The Relation Between Mechanical Properties and Microstructural Control. 10. Deformation of Amorphous Materials. 11. Electrons in Solids. 12. Electronic Transport. 13. Electrical Properties of Junctions. 14. Magnetic Properties of Materials. 15. Optical Properties.

Computational fracture mechanics

Abstract: Numerical procedures for accurate determination of elastic stress intensity factors for the general two-dimensional crack problem are reviewed. The elastic perfectly plastic state of crack tip deformation is studied by a finite element procedure. Elastic-plastic fields in the immediate vicinity of a crack tip are determined numerically by finite element procedures based on asymptotic studies of crack tip singularities in plastic materials. The small-scale yielding problem is modeled, and expressions for crack tip opening displacement, shear singularity amplitude, and plastic zone extent are derived. A finite element solution to the large-scale yielding of a circumferentially cracked round tension bar is obtained. The three-dimensional aspects of flawed structures and numerical methods of treating them are studied. Ductile fracture mechanisms, in particular crack tip fracture on the microscale, are discussed.

Fatigue at High Temperature

Abstract: This paper reviews the current state of the art of high temperature fatigue. Attention is given to the relative rotes of crack initiation and crack propagation, to damage processes resulting from cyclic strain including that of the substructure, of cyclic strain aging, at grain boundaries, by the environment, from wave shape effects and from plastic instabilities. The phenomenology of high temperature fatigue discussed includes formulation of fatigue equations and material representation, effects of environment, role of frequency, and of wave shape. The state of fatigue life prediction methods is considered with attention given to the most recent approaches to the problem.

Deformation mechanisms in oriented high-density polyethylene

Abstract: The deformation of samples of oriented high-density polyethylene has been analysed in terms of three principal deformation mechanisms,fibrillar slip, lamella slip andchain slip. From a study of small- and wide-angle X-ray diffraction patterns it is possible to deduce which mechanism or mechanisms are operating in particular cases. Material prepared in three different ways has been examined and it appears that in all three cases the primary mechanism for plastic deformation is [001] chain slip.

Model studies on mechanics of jointed rock

Abstract: A generalized physical model is tested triaxially in order to relate properties of the intact material and of the discontinuities to the strength and deformability of a jointed rock mass. The behavior of jointed models can be divided into three characteristic zones. At low confining stresses there is either sliding along preexisting joints or brittle failure through intact material and across joints with strength depending on the number of intersected joints. At intermediate confining stressed sliding or failure may occur again, but the failure mode changes from brittle to ductile. At high confining stresses no sliding and only ductile failure occurs. The three zones and the upper and lower bounds of strength are easily obtained by a few confined compression tests on the intact material, by sliding tests along joints, and by a direct tension test. If this characteristic behavior is valid for other materials, as seems likely because of the basically similar underlying mechanism, it may become possible to determine the behavior of a jointed rock mass by relatively simple experiments.

Effect of Pyrolytic Temperatures on the Longitudinal Strength of Dry Douglas-Fir

Abstract: Compressive and tensile strength of dry Douglas-fir was measured through rapid constant deformation rate tests at temperatures from 25 to 288°C, at initial thermoequilibrium and after 2 h of heating. The tensile strength decreased slowly with increasing temperatures to 175°C. Above 175°C, the tensile strength reduces rapidly. This is attributed to alteration of the cellulosic fraction of wood. The compressive strength decreases more uniformly with temperatures increasing to 288°C due to changes occurring in all three basic wood components with change in temperature. A first-order reaction equation for bond rupture/formation was adopted to describe the response. Including only terms for bond rupture resulted in good correlation to the observed strength response at reaching thermoequilibrium.

Thermal Instability Strain in Dynamic Plastic Deformation

Abstract: When a metal is deformed slowly, geometrical and material effects combine to limit the plastic deformation. It can be shown that for a given deformation geometry the limiting, or necking, strain will be a function of the workhardening exponent, n,* in the constituitive relation.

On a finite strain theory of elastic-inelastic materials

Abstract: An attempt is made to develop a theory of inelastic behavior of crystalline materials subjected to arbitrary deformation. The introduced concept of elastic motion leads to a simple decomposition rule: the total velocity gradient is the sum of the elastic velocity gradient and the inelastic velocity gradient. The important role of rotations and relevant constitutive relations is discussed and illustrated by an example of a tensile test of a single crystal. The assumption usual in plasticity that plastic deformation does not change the volume of the body follows in the present theory as a consequence of the second law of thermodynamics and material symmetry.

Relation between hysteresis and the dynamic crack growth resistance of natural rubber

Abstract: Under cyclic deformations in which natural rubber is allowed to relax fully, the minimum energy for the growth of cracks by a tearing process is about 0.04 kN/m. It does not involve hysteresis. For natural rubber held at constant deformation the corresponding energy is about two orders of magnitude higher. This increase is attributed to hysteresis caused by strain-induced crystallization. The energy requirements for growth when the rubber is subjected to dynamic deformations where incomplete relaxation occurs are found experimentally to be intermediate. A theoretical explanation is proposed which accounts for the experimental observations. It takes into consideration the effective crack tip diameter and the extension and retraction stress-strain curves which have a maximum close to break.

Quantitative characterization of the substructure of AISI 316 stainless steel resulting from creep

Abstract: The substructure of AISI 316 stainless steel resulting from creep deformation has been quantitatively characterized using transmission electron microscopy. The specimens were tested at temperatures and stresses ranging from 593° to 816°C and 8000 to 35,000 psi, respectively. Subgrains whose boundaries are predominantly (111) twist boundaries were formed in all tests at and above 704°C but were observed very infrequently at 650°C and were completely absent after creep at 593°C. The subgrain diameter,d, and the mobile dislocation density, ρ, were found to vary with the applied stress, σa, according to:d =kσa-1 and ρα σa2. Subgrain misorientation varys from less than 0.1 to 1 deg in each specimen seemingly independent of all parameters evaluated. A double triple node dislocation configuration was frequently observed in all specimens. Its relation to the deformation process is discussed in a mechanism involving the breaking of attractive dislocation nodes.

The plastic deformation of NiAl single crystals between 300°K and 1050°K: I. Experimental evidence on the role of kinking and uniform deformation in crystals compressed along ⟨001⟩

Abstract: Single crystals of stoichiometric NiAl have been compressed in the temperature range 300°K to 1050°K. Contrary to previous work it has been found that in this range of temperature the flow stress o...

Non-elastic deformation of concrete under cyclic compression

Abstract: Synopsis It is shown that, in comparison with a static stress, cyclic loading accelerates the non-elastic deformation of concrete. The resulting creep can be expressed as the sum of a mean-stress component and of a component which is dependent both upon the range of stress and upon the value of the mean stress.

Transverse field effects in nematic liquid crystals

Abstract: A novel electro‐optic effect has been observed in thin homeotropic nematic layers. Electrodes, such as a pair of parallel lines, are located on a planar surface in contact with the liquid. Deformation of the homeotropic ordering occurs when the applied field exceeds a threshold strength. Induced optical birefringence and diffraction have been observed, and electrically controlled optical transmission and reflection have been attained. Experimental data are given for a cyano‐aniline mixture with e∥ − e⊥ > 0 and for negative‐anisotropy materials.

An electron microscopy study of chip formation

Abstract: Chip formation or metal cutting is a unique large strain, high strain rate plastic deformation process. Almost all the previously reported studies of chip formation have examined the problem from the point of view of the mechanics of the deformable bodies using the mathematical theory of plasticity. This study, recognizing the heterogeneous nature of chip formation as encountered in course of machining metals, examines the problem from the metal physical or metallurgical view point. Electron microscopy studies were carried out on steel as well as nonferrous metal chips produced by shop machining conditions and compared to those chips produced by ultramicrotomy. This thin film orthogonal cutting process was employed to produce chips for microscopic examinations under well controlled and repeatable experimental conditions. The experiments carried out were designed to clarify the details of the heterogeneous plastic deformation activity occurring on the microscopic level during machining. The morphological (external surface) characteristics of the chips observed with the scanning electron microscope were correlated with the internal, dislocated structure of the chips observed by transmission electron microscopy methods. The effect of a stacking fault energy (SFE) change in an Ag-Sn alloy on chip thickness ratio(ν t) is presented for the first time, demonstrating that this deformation process is sensitive to changes in SFE. The essentially discontinuous nature of the chip formation process observed by scanning and transmission electron microscopy is analyzed with a model involving dynamic dislocation behavior in a metal in the presence of large energy dissipation arising from plastic flow to account for the observed instability.

Precise measurement of plastic behaviour of mild steel tubular specimens subjected to combined torsion and axial force

Abstract: In the present paper, as an investigation for obtaining detailed information about the plastic behaviour of real materials, precise measurement of plastic deformation of thin-walled tubular specimens of initially-isotropic mild steel was performed under combined loading of torsion and axial force having trajectories consisting of two straight lines at a constant rate of the effective strain. From the experimental results, it is found that the effect of the third invariant of the strain tensor appeared even for proportional deformation consisting of torsion and axial force. Moreover, it may be seen that the effective stress drops suddenly with increasing effective strain, and coaxiality between the stress deviator and the plastic strain increment tensor is seriously disturbed just after the corner of the strain trajectory. However, these local disturbances are recovered along the second branch of the trajectory. The effect of the third invariant of the strain tensor was eliminated from the experimental results by the introduction of the modified local stress space for isolating the influence of anisotropy due to the deformation history. This permits a systematic evaluation of the influence of anisotropy for various types of combined loading.

The plastic deformation of NiAl single crystals between 300°K and 1050°K

Abstract: The experimental results detailed in the preceding paper are interpreted in terms of glide and climb of disolcations of b = (100). It is shown that the same slip systems operate both when hard crystals deform uniformly and when kinking occurs. In the case of uniform deformation climb also causes significant plastic strain. The localized deformation associated with kinking is shown to be due to geometrical softening. On the basis of these conclusions the fact that a change of temperature, or change of strain rate, can give rise to kinking in a specimen which would otherwise deform uniformly (as shown in I) can be simply explained.

Relationship between deformation twinning and the stress-strain behavior of polycrystalline titanium and zirconium at 77 K

Abstract: The 77 K stress-strain curves of high purity Zr, commercial purity Zr, high purity Ti and commercial purity Ti, which are all significantly different, were analyzed by the Crussard and Jaoul method. The evolution of the mechanical twin structure in these specimens was also studied using quantitative optical microscopy. It was generally observed that changes in the nature of the twin structure development correlated with changes in the C-J deformation stages. Constant work hardening rate stages tend to appear at higher strains if the rate of increases of the twin volume fraction is large.