Compressive Plastic Deformation Research Articles

低合金鋼の空気中および３．５％食塩水中での疲労破面のＸ線フラクトグラフィ

Fatigue crack propagation tests of a low alloy steel (JIS SNCM 439) tempered at 200°C and 600°C were conducted both in air and in 3.5% NaCl solution. The residual stress near the fatigue fracture surface was measured by the X-ray diffraction method. The results obtained are summarized as follows:(1) The residual stress measured on the fracture surface was tension both in air-fatigue and corrosion fatigue. The tensile residual stress increased with the maximum stress intensity factor Kmax in the case of the material tempered at 200°C, while it had a maximum value at about Kmax=30MPa√m in the case of the material tempered at 600°C. When compared at the same Kmax value, the residual stress was lower for a lower stress ratio and in corrosion fatigue.(2) The distribution of the residual stress beneath the fatigue fracture surface was able to be decomposed into two components: the tensile residual stress in the vicinity of the fracture surface caused by monotonic tensile plastic deformation, and the compressive residual stress in the vicinity of the fracture surface caused by stress relief due to roughness and by compressive plastic deformation.(3) The maximum depth of the plastic zone was evaluated on the basis of the residual stress distribution. The depth ωy is related to Kmax by the following equation:ωy=α(Kmax/σY)2where σY is the yield strength obtained in tension tests. α is 0.19 for air fatigue and 0.06 for corrosion fatigue. The small value of α in corrosion fatigue suggests the hardening of the material in the plastic zone due to the environmental effect.

Notch-plasticity effect on closure of short fatigue cracks.

A model is proposed to evaluate the effect of notch plasticity on the development of crack closure for a short fatigue crack propagating from a notch root under the zero mean stress or compressive mean stress. The model assumes that a fatigue crack closes completely at the minimum applied stress and that compressive plastic deformation take place near the notch as if there were no crack. Plastic yielding of the Dugdale type is made from the root of an elliptical notch in an infinite plate. The crack opening stress and the effective stress intensity range are computed as functions of crack length, applied stress, and notch geometry.

Inhomogeneous deformation of grains and roughening of free surface of polycrystalline copper during compressive plastic deformation.

Inhomogeneous deformation at the free surface of copper specimen during compressive plastic deformation is studied. The inhomogeneous deformation of grains in the plane of specimen surface is observed by scanning electron microscope, while the inhomogeneous deformation perpendicular to the surface is studied by measuring surface roughness. It was found that the variations of the measured values of strain in each grain as well as the surface roughness in crease with the applied strain. Discussion is made on the relation between the variations of strain in each grain and the surface roughness.

Energy loss by plastic deformation in radial compression of a cylindrical shell

Energy loss by plastic deformation in radial compression of a cylindrical shell

Evaluation of 50 low and high copper amalgams according to Standards

The content and rationale of Standards for Dental Amalgam Alloys are discussed. The properties of amalgams made from 50 alloys used in Australia were determined according to methods in the Standards and the results are presented to enable comparison between low and high copper amalgams. The limits for the physical tests are discussed in the light of the range of values obtained. In general, the high copper amalgams showed higher one hour compressive strengths, lower creep and plastic deformation than low copper amalgams. No difference in dimensional change was found.

Deformation plastique du systeme biphase fer-argent de composition equivolumique

Plastic deformation in compression has been studied in a two phase Fe-Ag system containing phases of equal concentration (50%) by volume which are closely interconnected. During deformation at ambient temperature and at a given strain rate, the phases are redistributed into alternating layers of iron and silver, normal to the direction of compression. It is believed that the yield strength is controlled by the iron, and that strengthening is governed by the silver at strains greater than about 30%. The redistribution of phases occurs in a different manner at 614°C under a constant tensile stress: the silver phase surrounds the dispersing iron phase. The strain rate increases during deformation.

On the Ductility of the Intermetallic Compound Ni<SUB>3</SUB>Al

Compressive and tensile tests were performed using both single and polycrystal specimens of an intermetallic compound Ni3Al which is usually believed to be brittle, and especially the ductility was examined by comparing the elongation of specimens with fracture surface observations. Main results obtained are summarized as follows.(1) Polycrystalline specimens homogenized after casting do not show any elongation by tension at every temperature, and the fracture surfaces exhibit an intergranular fracture mode. On the other hand, compressive plastic deformation is possible to some extent, though intergranular fracture is also accompanied.(2) Single crystal specimens show about 100% elongation at and below room temperature. At higher temperatures, the elongations markedly decrease with increasing temperature and attain minimum values at the peak temperature of yield stress. Fracture modes are all ductile ones, showing a dimple pattern observable at a large magnification.(3) Polycrystal specimens, which were obtained by recrystallization annealing of the cold rolled single crystals, show about 15% elongation even at room temperature. Fractography shows transgranular as well as intergranular fracture. Thus, the lack of ductility in Ni3Al polycrystals seems to be caused mainly by segregation of impurity atoms to the grain boundary.

Experimental investigation of the structural aspect of fracture initiation in specimens of hard alloys of WC-20% Co loaded in unixial compression

1. In compression tests, fracture and plastic deformation of individual carbide grains occur long before the appearance of the main crack. 2. The carbide grains which undergo plastic deformation are, as a rule, locally loaded in multiaxial compression. 3. Fractured carbide grains are loaded in three-point or cantilever bending or by crack opening.

Inelastic Cycles of Axially Loaded Steel Members

Sixteen fixed-ended steel bars of rectangular cross section 1/2 in. x 1 (12.7 x 25.4-mm) and (12.7-mmand of various lengths were tested under 25.4-mm) nder static and dynamic loads to determine the cyclic hysteretic response of steel columns. The specimens were subjected to tensile yielding, post-buckling deflection cycles. Column slenderness ratios ranged from 85 to 210. This research complemented a corresponding elasto-plastic theoretical development; the experimental results generally agreed with theoretical predictions, yet significant deviations were noted. Principal findings were that the buckling load decreased with number of cycles, the columns exhibited net tensile or compressive plastic deformation in a cycle depending on deflection level, and the static and dynamic responses were similar.

On the limit of plastic deformation in compression of circular cylinders

Experiments were conducted to determine the effect of interface friction and speciment geometry on the useful ductile flow limit of 1100 aluminum and 1095 steel at room temperature. The tests consisted of measuring the equatorial strains during simple upsetting of circular cylinders. From the measured strains the surface stress components were calculated. All occurrences of fracture were observed to be the normal type. In some cases no surface cracks were observed and a possible explantation is given in the paper.

Comprehensive plastic deformation of a bulk metallic glass

Compressive plastic deformation experiments between 77°K and 520°K have been conducted on a bulk Pd 0.775 Cu 0.06 Si 0.165 glass. It has been confirmed that plastic deformation in this glass is highly inhomogeneous. This leads, in some cases, to void formation along the stronger shear bands. Above about 200°K, plastic deformation proceeds by jerky flow reflected in serrated stress—strain curves. Below this temperature, serrated flow is suppressed. This effect is reversible with temperature. Localized shear bands are found to be susceptible to preferential etching. It is suggested that this is due to the destruction of “short range” order of the glassy structure. Between 100°K and 520°K the ratio of the flow stress to the elastic modulus is ≈ 1 60 independent of temperature. Some factors that may contribute to the shear yield strength of the present and similar glasses are discussed.

Effective Factors for Crack Propagation under Varying Load Conditions

To clarify the effective factors for the crack propagation under varying load conditions, crack propagation is investigated using V-notched specimens and radial holed ones of 0.55% carbon steel and the following results are obtained. (1) The most important effective factor for the crack propagation under high-low type varying load condition is the essential increase of the stress at the crack tip for the opening of cracked surface caused by the repeated compressive plastic deformation. (2) In the case of steel specimens, there is no effect for the crack propagation under varying load condition caused by structural changing and it is also possible to estimate the crack propagation quantitatively considering the effect of crack opening. (3) It is also possible to estimate almost all the experimental results under varying load conditions qualitatively considering the effect of crack opening and existence of incubation period. (4) The effect of crack opening appears in the case of reversible stress condition but does not appear in the case of pulsating tension stress condition. This can be predicted by the calculation of the actual stress at the crack tip under varying load conditions.

Deformation in wrought Mg−9Wt Pct Y

Considerable tensile-compressive yield strength anisotropy is normally associated with textured wrought magnesium alloys.1 The ease of {1012} twinning is responsible for the lower compressive yield strengths of these materials. In Mg-9 wt pct Y, however, approximately equal tensile and compressive yield strengths of about 50 ksi have been previously reported.2 This investigation was performed to study the deformation of wrought Mg-9 wt pct Y with the purpose of understanding its unusual isotropic behavior. It was found that almost no {1012} twinning occurs in this alloy, thus accounting for the absence of anisotropy. Initial plastic deformation both in tension and compression occurs almost entirely by slip, primarily on the basal plane. Subsequent deformation occurs by a combination of slip and {1121} twinning with short {1012} twins appearing only occasionally.

Recovery of hydrogen permeability of ferritic alloys of iron with molybdenum and nickel

The effect of plastic deformation in compression and of subsequent annealing on the hydrogen permeability parameters of armco iron and its alloys with nickel and molybdenum was studied. In addition, the recovery of electrical resistance and X-ray line broadening was studied and the degree of weakening under conditions simulating those obtaining during the diffusion measurements was determined. It was concluded that the vacancy structure plays a predominant part in determining the hydrogen mobility in the alloys studied.

The effect of plastic deformation on self-diffusion in silver

The self-diffusion coefficient of silver undergoing plastic compressive deformation was measured over temperatures ranging from 810 to 1172°K and at strain rates from 0.00075 to 0.006 hr −1. At all temperatures it was found that the diffusion coefficient is proportional to the strain rate. The results were interpreted on the basis of a model in which two vacancy-production mechanisms and two vacancy-annealing mechanisms are assumed to be operative. At low temperatures, vacancy production is assumed to occur by a geometric, temperature-independent process, and the annealing mechanism is assumed to be the migration of vacancies to fixed sinks. At high temperatures, it is suggested that vacancies are formed by a thermally activated process and that they anneal by combining with a highly mobile defect. Energetic considerations lead to the conclusion that this mobile defect is probably a divacancy.

Density and Hardness Changes Produced by Plastic Deformation in KCl Crystals

A study has been made of the density changes which accompany plastic deformation in compression of potassium chloride crystals and of their annealing. Also hardness changes, their annealing, and slip-line formation have been investigated. Up to about 11% deformation, the slip is predominantly simple with some admixture of double slip, and no change of density is observed. At 11% deformation, multiple slip presumably sets in accompanied by a rapid decrease of density. The rate of formation of vacancies is 3.02 \ifmmode\times\else\texttimes\fi{} ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ per percent deformation. A comparison of this value with the results of the experiments of Ueta and K\"anzig leads to the ratio of about four vacancies per electron trap. Vacancies seem to have no measurable influence on hardness which thus appears to be primarily associated with changes in the dislocation density or their configuration during plastic deformation.