Residual Strain Distribution Research Articles

Prediction of massive hydraulic fracturing from analyses of oriented cores : Logan, J M; Teufel, L W Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V1, P340–344. Publ Reno: University of Nevada, 1978

An attempt has been made to predict the orientation of massive hydraulic fractures stimulated between depths of 2316 and 2464 M within the Muddy J formation of the Wattenberg Gas Field, Colorado. Predictions were based upon a study of the properties of 3 oriented cores and 2 unoriented cores. A preferred orientation of fractures induced in point-load tests is found for all 5 wells. The second phase involves investigation of the composition, grain size, microfracture orientation, crystallographic orientation, grain dimensional orientation, and residual strain. It is concluded that the fractures oriented at 335 on the east and west sides of the field are primarily controlled by the dimensional orientation of quartz grains, while those in the center of the field having an orientation of 110 are controlled primarily by the residual strain. Subsurface geology shows a buried fault trending northeast through the center of the field, postulated to have influenced the distribution of residual strain. In the eastern and central wells, good agreement was found with the predictions from the core analysis. 10 references.

New Measuring Method of 3-Dimensional Residual Stresses Based on Theory of Inherent Strain

The authors have already proposed the general principles in measurement of residual stresses. In this paper, the authors developed a new method for selection of observing positions of strains to ensure highly accurate measurement by using the theory of inherent strain, which is based on one of these principles.By this selection method, it is seen that the more number of measurements ensures the better average accuracy of estimated values. However, there are many positions where observed values scarcely influence the accuracy of measurement. These positions can be excluded from the measurements for reasons of economy and comparatively small number of observing positions can be selected by the present theory, which still secures a high accuracy of measurement.Furthermore, in order to measure three dimensional residual stresses in multipass welded joint, the proposed measuring method can be simplified by using the characteristics of the distribution of its inherent strains. According to this theory, three dimensional inherent strains can be divided into the components of inherent strains contained in the sliced cross section of the weld line and the longitudinal inherent strains contained in sliced plates parallel to the surface of the joint, and the measurement of three dimensional welding residual stresses has become practically possible.By this theory, the distributions of residual stresses and longitudinal inherent strains in multipass welded joint have been measured for the first time. And the estimated residual stresses show a good coincidence with the directly observed stresses on its surfaces.This implies that the present theory is reliable and applicable to measure such complex internal residual stresses.

Investigation of the deformation and failure of polypropylene under indenters of different shapes

In order to study the residual strain distribution in a nontransparent polymer (polypropylene) under identers of various shapes (sphere, cone, cylinder) multilayer colored specimens with a predetermined distribution of the layers were used. By cutting along selected planes it was possible to estimate the residual strains in the interior of the specimen, both qualitatively and quantitatively. By this means we investigated the relations between the reversible and residual strains in polypropylene as a function of the indenter penetration depth and, moreover, the relations between the deformed and failed volumes of polymeric material under indenters of different shapes. It was shown that a change in indenter shape may produce a considerable change (by a factor of 3 or more) in the relations between the penetration, strain propagation, and failure volumes, which should be taken into account both in determining the hardness of polymeric materials by different methods and in selecting the shape of sealing elements.

ステンレス鋼円板の点加熱による塑性ひずみ

The distributions of residual strain produced by spot heating are studied on an austenitic stainless steel plate. The relations between dimensions of plastic region and heat input are clarified experimentally to obtain the fundamental properties of welding deformation.Various diameters of concentric circles are previously marked on the surface of specimens for measuring the strain (Fig.2). The specimens are spot heated at their center with different heat inputs by means of a TIG arc welding set. The thermal cycle of each specimen is observed at several locations, and then the specimen is cut into concentric rings to release the residual stresses. In this procedure the changes in diameter of marked circles due to heating and cutting are measured and the components of residual strain on the concentric circles in the plates are calculated.The results obtained are as follows: The thermal cycle at any point of the plate can be presumed using the equation of heat conduction for instantaneous line heat source (Figs. 4, 5 and 6). The components of the total, elastic and plastic strains in circumferential and radial directions can be calculated from the changes in diameter of the concentric circle (Figs. 8 and 9). A plastic region is produced around the heated point and it causes residual tensile stresses, which are roughly equal to the proof stress of the material. The plastic region is extended in radius with an increase of heat input (Fig. 12). The observed maximum temperature at the boundary of plastic region is about 20 to 30°C, which is lower than the expected value. The measured results of residual stresses well agree with those derived in accordance with the inherent stress theory from the plastic strain distributions (Fig.10).

サブマージアーク溶接におけるひずみ挙動

As a basic research of strain characteristics in automatic arc welding process, which is executed in considerably higher arc current and welding speed than those of manual arc welding, the investigation has been experimentally carried out on submerged arc welding of mild steel plate under different heat inputs (Fig.1 and Table 2). Detailed observation covers the welding thermal cycles, the progress of longitudinal and transverse strains in base metal during welding and cooling as well as the distributions of the longitudinal total, elastic and plastic strains, the transverse shrinkage and the angular distortion after welding. Main results obtained are as follows.The transient mechanical strains of longitudinal and transverse directions occur respectively in tension and compression conversely to each other during the former stage of welding and, afterward, change into compression and tension according to the thermal expansion and shrinkage of the weld zone, which are inferable from the thermal cycles (Figs.3 and 8).From the distributions of longitudinal total strain and transverse shrinkage after welding, it is clear that the welded plate expands longitudinally in its middle and contracts in its outer portions, that is, the half of plate on either side of the weld line deforms into fan-shape, these rotational deformation being re-markable in case of large heat input (Figs.5 and 10). And also, the large heat input reduces the magnitudes of longitudinal plastic shrinkage occurring in the weld zone, extends transversely the region of its occurrence and consequently reduces the inherent shrinkage (Figs.11 and 12). The observed distributions of longi-tudinal residual stress and plastic strain along the transverse center line of welded plate, in case of low heat input, well agree with those theoretically derived (Tables 4 and 5).

Residual Strain Distribution in Layered Rings

Residual Strain Distribution in Layered Rings

Determination of Residual Stress of Aluminum Alloys by X-Rays

The distribution of residual lattice strains or lattice spacings and residual stresses in plastically extended aluminum alloys were measured by various characteristic X-rays. Then, the scattering of the distribution of the residual lattice strains vs. sin2ψ were investigated precisely in each stage of plastic strains, and the wave length and lattice plane dependency of the residual stresses were discussed.Hot rolled sheets of Al-1.2 Mn (3003) and Al-4.5 Cu-1.5 Mg-0.6 Mn (2024) alloy were used in this experiment. The shape and dimensions of specimens are shown in Fig. 1. The chemical composition, heat treatment and mechanical properties are indicated in Table 1, 2. To prevent the diffraction lines of these specimens from becoming spotty, the specimen holder8) was equipped with horizontally and vertically oscillating mechanism, by which sufficiently continuous diffraction patterns were obtained (Fig. 2).In order to make sure of the wave length and diffraction plane dependency of the residual stress, the data for several planes by CuKα, CoKα and CrKα radiation were sought and obtained (Fig. 5). On the observation of the distribution of residual lattice strains by sin2ψ method, the direction of the incident X-ray beam to the specimen surface ψ0 is devided at intervals of 5°in the range of 0°∼45°and their diffraction lines on the side of ψ0+η were observed (Fig. 3, 4). The results obtained in this study are summarized as follows.(1) In order to examine the detailed distribution of the lattice strains or lattice spacings, it is necessary to obtain many lattice strains vs. sin2ψ and to observe always only the sharp diffraction lines on the side of ψ0+η precisely.(2) It is confirmed that the distributions of the lattice strains vs. sin2ψ of annealed specimens are nearly linear, but scatter evidently in the early stage of the plastic strain about 2%, and aproach linear relation again with increase of the plastic strain. From these configuration, it is considered that the stress of a second kind9) in terms of Heyn intergranular stress takes place in the residual lattice strain.(3) The residual stresses are independent of the wave length but depend mainly on the lattice planes.

Lattice Strain Measurements on Deformed FCC Metals

AbstractIn this work experiments have been undertaken to determine the type of residual stresses of plastically deformed polycrystals of aluminum, copper, and nickel which cause a shift of the X-ray interference lines. In order to get accurate stress values, the lattice strain distribution has been measured in special planes of the deformed specimens, using the sin2 ψ technique. The surface stresses were determined as a function of the macroscopic plastic strain of cylindrical specimens. With increasing strain, the residual surface stress component parallel to the direction of deformation increases. The stresses observed are compressive ones after tension and tensile ones after compression.The changes in the residual lattice strain distributions which arise on progressive thinning of the plastically deformed specimens have been measured. From the stress values determined in each new surface layer, the stress distribution originally present in the uodestroyed specimen was calculated. Tensile stresses in the interior of the specimens are in equilibrium with compressive stresses in the surface areas. The formation of residual stresses on specimens with a work-hardened surface layer is found to be quite different from that of well-annealed samples.The results of this work seem to show that in uniaxially deformed cylindrical specimens, residual macrostresses arise which may be a consequence of a macroscopic inhomogeneity of work-hardening between the surface layers and the interior of the polycrystals.