Values Of Normal Stress Research Articles

Human errors versus stress

Abstract This paper discusses human errors in a man-machine system with the dependence on different stresses. A method is presented for defining ranges of normal stress values, based on the construction of the membership function from the fuzzy set theory. This method is applied to a stress analysis for a sample of station foremen in the railway traffic system of Slovenia. The results of this analysis are given.

SIMPLE DETERMINATION OF POWER LAW FLOW CURVES USING A PADDLE TYPE MIXER VISCOMETER

ABSTRACTA simple and accurate procedure to determine the flow properties of powerlaw fluids using a paddle type mixer viscometer is described. The approach considers the mixer as analogous to a concentric cylinder system and incorporates the inclusion of end effects in modeling. The procedure significantly reduces data collection because calibration with standard fluids is not necessary to estimate average shear stress and shear rate values.

Source Mechanism of the Cachar Earthquake of December 30, 1984, NE India from the Synthesis of Body Waves

Abstract Wave forms modelling of P and S wave data is done to study the seismic source parameters of a moderate earthquake of December 30, 1984 (mb = 5.6), which occurred in NE India. A combination of thrust and strike slip faulting is determined with fault plane striking N 12° E, dipping 50° west, slip 32° and focal depth of 20 km. The total source time duration is found to vary from 5 to 6 seconds. Average value of seismic-moment, fault radius, stress-drop, apparent stress, dislocation, strain energy and strain drop are 2.25 x 1025 dyne-cm; 8.1 km; 23 bars; 16 bars; 14 cm; 1.45 x 1020 ergs and 0.24 x 10-4 respectively. The axis of maximum compression (pressure axis) is acting a1most horizontal in southeast-northwest direction and axis of minimum compression (tension axis) in northeast-southwest direction. This earthquake possibly resulted from the westward overtbrusting of Burmese arc and the simultaneous counter-clockwise motion of NE Indian wedge, driven by the general plate motion of the Indian subcontinent.

The extensional properties of M1 obtained from the Carri-Med elongational viscometer

The extensional flow properties of the “round robin” fluid M1 were examined using the Carri-Med elongational viscometer at 20 ° C. With this particular fluid, use of a spinneret caused flow of a pulsating nature or a distortion of the filament, or both. Consequently, flow of the fluid was directly out of the tube. The filament was stretched using the rotating drum operating at various speeds. The amount of die swell observed depended upon the take-up speed. The measured diameter profile and the calculated strain rate curve showed distinct differences from those obtained with most other polymer solutions previously examined. The apparent extensional viscosities were determined, and showed Trouton ratios in the range 300–10 000. As a function of total strain, the fluid appeared to strain harden up to a strain of about 2.5, and then pass through a maximum, before strain thinning slightly. Average values of stress and strain rate were also determined using a two-point method. The results from this showed the apparent extensional viscosity to increase as a power law function of strain rate, although the value of the power law index did depend upon the choice of the two points selected. The particular collection of flow characteristics observed in this fluid are, if not unique, then certainly unusual in a number of aspects. Overall, the material is undoubtedly strain hardening, although the exact form which this takes, particularly at low strains, would appear to be a direct consequence of the relaxation time of the fluid.

Effects of X-ray beam collimation on the measurement of residual stress distribution in a Si3N4/steel joint.

X-ray collimation and diffraction conditions were optimized to evaluate the detailed distribution of residual stress quantitatively around the ceramic/metal interface, and the results were applied to the Si3N4/Cu/steel system. The residual stress value increased and finally saturated as the collimation and irradiation area decreased in the Si3N4 region close to the interface of the joint. The normal stress value across the interface saturated below 0.2 mm2 to 240 MPa for Si3N4/t0.2 mm Cu/steel, and to 400 MPa for Si3N4/steel. It is recommended that φ0.1 mm collimation is suitable to evaluate its detailed distribution along the interface in which the irradiation area is 0.016-0.031 mm2. Several characteristic features of distribution were successfully observed along the joined interface of Si3N4/t0.2 mm Cu/steel having a lapped surface; first large tensile normal stresses at both edges, secondly the minimum stress points 1-2 mm inside the edge which was originated by stress relief through a localized plastic deformation of the Cu buffer, and thirdly the maximum normal stress across the interface in the center region of the specimen which had never been predicted and could be caused by the three dimensional effect of the joined plate.

Heavy Axle Load Wheel-Rail Contact Stresses and Their Tread-Crown Curvature Relationships

This paper presents a theoretical/design analysis of wheel-rail contact stresses and geometries for U.S. freight cars of 70, 95, 100, and 125 ton freight capacities operating on various crown rails. After discussing various types of rail stresses, it is pointed out that the contact stresses are the major factor and the only parameter that enables a designer to improve or optimize the rail life and performance. In order to determine the most suitable diameters for the heavier cars, an engineering lower bound analysis of the contact has been completed. It uses in a two-dimensional Hertzian analysis, the field information of well worn-out wheel and rail contacts which are almost rectangular and of 1 in. width. The lower engineering bound values of maximum normal contact stresses for the 100 and 125 ton cars using wheels of diameters from 33 to 42 in. are given. This stress for the current 100 ton car with 36 in. diameter wheels is 98.35 ksi. To approach this value for the 125 ton car it is necessary to use 42 in. diameter wheels which is strongly recommended for the U.S. railroads. A Hertz theory based analysis of the contact stresses with varying wheel diameter, tread profile radius and rail crown radius for the 70, 95, 100, and 125 ton cars has been presented. Using the field information that the difference in radii of curvature of worn wheel and rail is approximately 5 in., choice of radii of rail and wheel profile curvatures is made so that the design radii difference is always 5 in. or more. Wheel diameter and wheel profile radius ranges used for this analysis were 33 to 44 in. and 15 to 35 in., respectively. The rail crown radius range was 10 to 30 in. It was concluded that a rail crown radius of 15 to 20 in. and wheel tread profile radius of 22 to 30 in. are good initial ranges for further analysis of design.

A critique of bond strength measurements

The lack of consistent values for dentine bond strengths in shear or in tension from what are superficially identical experimental procedures has led to ambiguities in the interpretation of the data. These variations in bond strength are usually considered to be related to different adhesive procedures. However so far little attention has been paid to the detail of the test procedures used. In this study the sensitivity of bond strengths to changes in testing conditions has been calculated using finite element stress analysis. It is shown that tensile and shear bond strengths are highly dependent on the geometry of the test arrangement and the materials involved. It is concluded that the concept of ‘average stress’ for the measurement of bond strength does not stand up to close examination. The measurement does not provide a material property as its value is dependent on local conditions and the actual stresses have little relationship to the average stress value. This demonstrates that there is a need for the standardization of test procedures for the measurement of bond strengths so that a universally valid comparison between different bonding agents can be performed.

Cotton Water Stress Under Trickle Irrigation

ABSTRACT Cotton was trickle irrigated two to three times weekly in 1984 and 1985 using buried perforated tubing under each row. Water application rates were about 0.6, 1.0, and 1.3 times estimated consumptive use (CU). The cotton was monitored for water stress using the crop water stress index (CWSI), soil water content, and yield. Significant differences in seasonal average crop water stress values, average soil water contents, and yields were obtained for the three water treatments. The wettest treatment with average CWSI values near 0.1 gave the highest yield and had the highest soil water contents before irrigation. The yield increased nearly linearly with decreasing CWSI while the water use efficiency (yield per unit of water) was highest for the 1.0 CU treatment.

The predictive value of quantitative computed tomography for vertebral body compressive strength and ash density

Whole lumbar vertebral sections (L 2 and L 3) were obtained from 30 elderly individuals aged 43–95 years, mean 81 years (13 females, 17 males). None of the subjects had had malignant diseases. Quantitative computed tomography (QCT) was performed on an EMI 7070 scanner. One 8 mm slice parallel to the end-plates was obtained from the center of each vertebral body. The trabecular bone mass in each slice was outlined interactively by means of a tracer-ball. A CT-histogram was recorded inside this area, and average CT-values were expressed in Hounsfield Units (HU). The whole vertebral body (L 2) was compressed in a materials testing machine. From the central part of L 3, vertical cylindrical pure trabecular bone specimens were obtained. The biomechanical competence of these specimens was also assessed by means of a materials testing machine. Finally, all bone specimens were incinerated for determination of apparent ash-density. Highly significant positive correlations were found between average CT-values and (a) stress values of the trabecular bone ( r = 0.81, p < 0.001) and (b) ash-density of the pure trabecular bone ( r = 0.81, p < 0.001). Furthermore, a significant positive correlation was found between CT-values and (a) total vertebral body load ( r = 0.72, p < 0.001), (b) total vertebral body stress (load/cross-sectional area) ( r = 0.55, p < 0.001) and (c) ash-density of the whole vertebral body ( r = 0.76, p < 0.001). It is concluded that quantitative computed tomography gives valid predictions of both vertebral trabecular bone mass and mechanical competence. The predictive value for whole vertebral body load, stress and ash-density, although less marked, is still highly significant.

Modelling of stress patterns along the western part of the north anatolian fault zone

The stress field before and after strong ( M ≥ 6) earthquakes in the western part of the North Anatolian Fault Zone is modelled. Assuming an initially homogeneous state of stress, the elastic co-seismic stress-drops, the inelastic post-seismic stress variations and the increase of stress due to plate motion are taken into account, using the theory of dislocations. The model consists of an elastic layer (upper crust) above a half-space which is described by elastic properties and alternatively by a standard linear solid. The results of the latter inelastic model differ only slightly from that of the purely elastic one. One of the main results is that most of the earthquakes fall into regions for which the model calculations predict high stress levels prior to the events. At present, the highest stress values are obtained for an area around 34° E to 35° E. They are higher than the average pre-seismic stress value for the series of eight earthquakes investigated in this study. All results are critically dependent on the assumption of the initial stress field being homogeneous along the western part of the North Anatolian Fault Zone.

The formation of areally-averaged roughness lengths

It is argued that the best area average of the roughness length zo in heterogeneous terrain is that which, if it applied in homogeneous terrain, would produce the correct spatial average value of the surface stress. A heuristic argument is presented to show that this effective value of z0, zeff0, can be obtained by averaging drag coefficients based on a ‘blending’ height. The blending height of about L/200, where L is the horizontal scale of the roughness variations, is the characteristic height at which the flow changes from equilibrium with the local surface to independence of horizontal position. These calculations are compared with numerical simulations of planetary boundary layer flow over variations in roughness length and show good agreement. The values of surface stress which result are always greater than those which would be deduced by assuming a local flow equilibrium through the whole depth of the boundary layer. For variations of z0 on short length scales, zeff0 approaches the largest values of z0 within the averaging area.

Stress distribution in multilayered composite material with curved structures (model of a piecewise homogeneous body)

In the case of single-phase (antiphase) curvature in the structure of the composite under consideration, an increase of concentration of the filler entails a decrease (increase) of the values of the self-balanced normal stresses and, conversely, an increase (decrease) of the values of the self-balanced tangential stresses. With η(2) ≤ 0.1 (where η(2) is the concentration of the filler) a decrease of the parameter k=2πH(2)/l (where 2H(2) is the thickness of the layer of filler, l is the wavelength of the forms of curvature) entails a monotonic increase of the self-balanced tangential stress in the case of single-phase curvature. This means that with fixed wavelength of the forms of curvature (with fixed thickness of the layer of filler) a decrease in thickness of the layer of filler (an increase of the wavelength of the forms of curvature) entails a monotonic increase of the tangential stress. The correlation between the self-balanced normal stresses and the parameter k in the case of antiphase curvature with all the considered values (0.02 ≤ η(2) ≤0.5) is nonmonotonic. It follows that with fixed l there exists such a thickness of the layer of filler H(2) at which the self-balanced normal stress σnn has its maximal value. With increasing ratio of the moduli of elasticity of the material of the filler and of the matrix, and also with increasing parameter e=L/l (where L is the length of the sagitta), the values of the self-balanced normal and tangential stresses in both cases under consideration increase. When the curvatures in the structure of the investigated composite materials are very small, the normal stress (in the case of antiphase curvature) and the selfbalanced tangential stress (in the case of single-phase curvature) may be a multiple of the normal stress σ11(1)0 in the matrix which acts in the direction of the Ox1 axis and is balanced by the external forces 〈p〉.

Combined Lagrangian multiplier and penalty function finite element technique for elastic impact analysis

A new finite element procedure which combines the Lagrangian multiplier method and the penalty function method for dynamic contact analysis with friction is presented in this paper. As a result of this combination, the whole contact system can be analyzed as one body in both contact and separation states. No displacement constraints are required on the striker and no extra stress due to gap elements is created. Coulomb's friction law is employed to set up sliding and sticking conditions and discrete impact and release conditions are implemented. A two-dimensional analysis for the longitudinal impact of two rods is solved as a numerical example. The average values of stress and the time durations are very close to the theoretical solution.

The formation of areally‐averaged roughness lengths

AbstractIt is argued that the best area average of the roughness length zo in heterogeneous terrain is that which, if it applied in homogeneous terrain, would produce the correct spatial average value of the surface stress. A heuristic argument is presented to show that this effective value of z0, zeff0, can be obtained by averaging drag coefficients based on a ‘blending’ height. The blending height of about L/200, where L is the horizontal scale of the roughness variations, is the characteristic height at which the flow changes from equilibrium with the local surface to independence of horizontal position. These calculations are compared with numerical simulations of planetary boundary layer flow over variations in roughness length and show good agreement. The values of surface stress which result are always greater than those which would be deduced by assuming a local flow equilibrium through the whole depth of the boundary layer. For variations of z0 on short length scales, zeff0 approaches the largest values of z0 within the averaging area.

Non-linear viscoelasticity of polysaccharide solutions. 2: Xanthan polysaccharide solutions

The viscoelastic properties of aqueous solutions of the microbial polysaccharide xanthan have been studied using a wide range of rheological experiments including small deformation oscillatory, steady and transient shear techniques. Part I of this series described the classic ‘random-coil’ polymer response of guar galactomannan solutions under these experimental regimes. The high sensitivity of xanthan solutions to strain and to shear (strain) rate confirm previous observations that its rheological properties are more akin to those of a ‘weak gel’ than of a more conventional entanglement polymer solution, as exemplified by guar. In particular the strain at the peak shear stress γ ∞ (‘overshoot strain’) was found to be around 0.5, and with a minimal peak in the normal stress at γ N ⋍ 1 compared with values of γ ∞ around 2–3 and very high normal stress values of γ N for entanglement coupled semi-dilute solutions (including guar/water) and synthetic polymer melts/solutions. Stress relaxation measurements reveal extremely long (gel like) modes of residual stress in the relaxation spectrum. The observations are consistent with earlier data, and the postulated model of more specific inter-chain couplings between xanthan molecules occurring in solution.

The effects of plant moisture stress on red pine (Pinusresinosa) seedling growth and establishment

Red pine (Pinusresinosa Ait.) 2-0 and 3-0 bare-root and 1-0 containerized seedlings were subjected to five different watering regimes (drying cycles). Overall, moisture stress as measured with a pressure bomb was highly correlated with seedling growth and survival. While shoot elongation during the drought period was unaffected, stressed seedlings showed pronounced decreases in cambial activity, secondary needle elongation, subsequent bud formation, root length, and number of active mycorrhizal root tips per centimetre compared with control treatments. This resulted in reduced top and root dry-matter production. Watering treatments with average seasonal internal moisture stress values in the range of −8 to −11 bar (1 bar = 100 kPa) showed no measurable reductions in seedling growth. Consistently, less internal moisture stress in the containerized seedlings indicate they are better able to avoid drought. Overall, performance of the 2-0 bare-root seedlings was superior to that of the 3-0 and containerized stock.

Wave propagation from an explosive source

The model proposed describes the radiation of the primary seismic pulse from an explosive source. The model incorporates a viscous Voigt liquid in description of the nonelastic rock deformation that the explosion causes. The problem is solved in the frequency domain, followed by Fourier synthesis to obtain waveforms. Comparisons of the theoretical results with field data in three sedimentary environments of shale, sandstone, and marl indicate good quantitative agreements in shape and duration of transient pulses. Values of angular normal stress obtained at the deformed boundary suggest a dynamic tensile strength of rocks that decreased with duration of the tensile stress transient. The radius of the deformed zone (B) scales with the charge size Q approximately as [Formula: see text] where n is [Formula: see text] or larger.

Flow Characteristics for the Complex Stress State in Metal Cutting

Although it is generally believed that shear flow stress is always independent of the normal stress on the shear plane (a condition assumed in slip line field analysis), this is not the case. Under the special conditions involved in metal cutting (high values of concentrated shear strain and moderate values of compressive stress on the shear plane) localized defect areas occur which give rise to a real sound area (A R ) that is less than the apparent area (A). This gives rise to an instability resembling that in a uniaxial tensile test of a ductile metal at the point of necking. A defect area is avoided only when the normal stress on the shear plane is large relative to the flow stress at large strains or if the strains involved are relatively small (ɛ ≂ 1.0) for relatively low values of normal stress on the shear plane. All of this is discussed in terms of experimental data. It is found that if no defect area is involved, a single linear stress-strain curve is obtained. However, when a defect area develops as in metal cutting, the normal stress on the shear plane plays a significant role. The reason for the maximum flow stress and apparent negative strain hardening in cases involving a defect area is discussed as well as a method of correcting shear stress-strain curves with defects and different levels of normal stress into the corresponding defect free stress-strain curve.

Use of inhomogeneous finite elements for the prediction of stress in rope terminations

An inhomogeneous element method of solving the strain and stress distribution of a cone‐like synthetic rope termination, which is designed and manufactured to enhance the strength of end connection of the rope, is described. The 8‐node quadrilateral isoparametric axisymmetric element was used. Different material constants were specified at different Gauss sampling points, so as to simulate the non‐homogeneity of the termination. The results indicate that maximum axial stress value in strand is much larger than the element average stress value. This element proved to be useful in calculating stresses and strains in reinforcing fibre strand embedded in resin matrix. The results obtained give some insight into the non‐uniformity of the stress distribution and will be meaningful to the designer of the rope end termination.

Behaviour of a lyotropic-smectic liquid crystal between mica surfaces A study of the fully hydrated egg-lecithin

The behaviour of three egg-lecithin (EL)—water (W) mixtures, 60% (w/w):I, 50% (w/w):II and 30% (w/w):III, squeezed out or sucked in between two mica surfaces was investigated using an apparatus designed by J.N. Israelachvili. Mixture I is a lyotropic-smectic liquid crystal (LSLC), in contrast to II and III in which the LSLC is in equilibrium with a separated phase of excess water. The force F applied to the micasheet holders, the “separation” D between the mica surfaces and the average refractive index were measured for 1 < D < 200 nm. A stepwise-thinning process was mainly observed on compressing mixtures I and II from separation 30 < D < 60 nm down to the minimum reproducible separation D min , 9.0 ± 0.7 nm, which corresponded to the flattening of the mica surfaces. The steps Δ D were equal to multiples of λ = 5.5 ± 0.4 nm for sample I and of λ = 5.3 ± 0.3 nm for sample II. The contact area of the flattened-mica sheets increased with the force F at separation D min . Assuming that an effective elastic parameter can be defined for our composite system (mica sheet + glue), we interpret the F —contact-area dependence using the theory of Johnson et al. and deduce values of average normal pressures or stresses of the order of 10 mN m −2 on the flat mica—mica contact. At such pressures the values of λ and the repeat distance of the LSLC formed by EL + W and measured by X-ray diffraction are similar. The refractive index n of I is independent of separation for D min < D < 50 nm but its value increases when D decreases for II and III. It appears that excess water is selectively extruded when F increases and D decreases. We suggest that, at maximum stress and D min = 9 nm, the two mica surfaces are separated by two poorly hydrated EL bi-layers, while the EL polar groups in contact with the mica surface are almost completely dehydrated.