Bending Stress Values Research Articles

Effect of Stress Frequency and Chemical Medium on the Corrosion-Fatigue Behaviour of 316L Stainless Steel

Among most used materials in implantology and the manufacture of surgical instruments, one finds the austenitic stainless steel AISI 316L, considered for its well adapted mechanical characteristics, its biocompatibility and in particular its resistance to uniform corrosion. The implants are often subjected to cyclic mechanical loads during normal activity of the human body, but they can also be attacked chemically by the physiological medium, under certain conditions. Between several mechanical and chemical parameters that can influence the corrosion-fatigue behavior of such material, the load frequency parameter is highlighted in this work. The aim is to determinate the effect of load frequency changes on the crack growth rate in corrosion-fatigue and to compare this effect in pure fatigue. To make experimental evidences, notched austenitic steel specimens have been submitted to cyclic bending tests inside a chlorine solution simulating the physiological medium (NaCl 0.9%). The bending stress value was taken equal to 200 MPa with a stress ratio R of 0, at different stress frequency values, respectively of 0.5, 1 and 2 Hz. When immersed in the chemical medium, the mechanical behavior of the steel sheets appears to be worst as the frequency decreases, as long as the crack size remains less than the critical one. In pure fatigue, the mechanical behavior changes with the increase of frequency and becomes detrimental. This corroborates different author works for such material.

Effect of Stress Frequency and Chemical Medium on the Corrosion-Fatigue Behaviour of 316L Stainless Steel

Among most used materials in implantology and the manufacture of surgical instruments, one finds the austenitic stainless steel AISI 316L, considered for its well adapted mechanical characteristics, its biocompatibility and in particular its resistance to uniform corrosion. The implants are often subjected to cyclic mechanical loads during normal activity of the human body, but they can also be attacked chemically by the physiological medium, under certain conditions. Between several mechanical and chemical parameters that can influence the corrosion-fatigue behavior of such material, the load frequency parameter is highlighted in this work. The aim is to determinate the effect of load frequency changes on the crack growth rate in corrosion-fatigue and to compare this effect in pure fatigue. To make experimental evidences, notched austenitic steel specimens have been submitted to cyclic bending tests inside a chlorine solution simulating the physiological medium (NaCl 0.9%). The bending stress value was taken equal to 200 MPa with a stress ratio R of 0, at different stress frequency values, respectively of 0.5, 1 and 2 Hz. When immersed in the chemical medium, the mechanical behavior of the steel sheets appears to be worst as the frequency decreases, as long as the crack size remains less than the critical one. In pure fatigue, the mechanical behavior changes with the increase of frequency and becomes detrimental. This corroborates different author works for such material.

고속철도 레일 표면 결함 관리기준에 관한 연구

레일 표면 결함이 발생할 경우 매우 높은 충격하중이 발생하여 레일 피로 진전 또는 레일 파단에 이를 수 있고 레일이 파단될 경우 열차탈선 등 대형 사고가 발생할 수 있으므로 레일 결함부에 대한 관리기준의 정립이 매우 중요하다. 본 연구에서는 차량-궤도 동적 상호작용 해석 프로그램을 이용하여, 실제 고속철도 자갈궤도에서 결함이 발생한 43개 지점에서 측정된 레일요철을 입력값으로 하여, 요철 깊이에 따른 충격 윤중과 레일 휨응력을 산정하였다. 궤도틀림을 감안하여 윤중 및 레일 휨응력의 한계값을 설정하고, 해석결과로부터 얻은 윤중 및 레일 휨응력 최대값과 결함 깊이 및 폭과의 상관관계를 분석함으로써 레일 표면 결함부에 대한 관리기준을 제시하였다. 분석 결과, 허용할 수 있는 요철 깊이는 충격 윤중에 의하여 발생할 수 있는 레일 두부의 소성 변형을 방지하기 위하여 관리되어야 하며, 엄격한 조건을 평가할 경우 그 값은 0.2mm 정도가 적당함을 알 수 있었다. The rail surface defects can cause the high impact load on the track and lead to the progress of the rail fatigue damage and the rail break. In case of the rail break, there is a great deal of risk for derailment, and thus the maintenance criteria for the rail surface defects are of great importance. In this study, using the dynamic train-track interaction analysis program, the impact wheel loads and rail bending stresses according to the depths of the surface defects have been calculated with the input data of the rail surface irregularities measured at 43 spots with surface defects in the ballasted track of high-speed railway. Considering the irregularity of track geometry, the allowable limits of wheel load and rail bending stress have been set, and the maintenance criteria for the rail surface defects was suggested by analyzing the relationship of the maximum values of wheel load and rail bending stress versus depth and width of rail surface defect. The analysis results suggest that the allowable depth of the surface defect is determined approximately 0.2mm from the limit of the impact wheel load.

Effects of Moisture Content and Urea Fertilizer on Bending and Shearing Properties of Canola Stem

Bending stress, specific shearing energy, and Young's modulus of canola (Brassica napus L.) stems were investigated. The specific shearing energy using pendulum method and bending force were measured for four moisture content levels (35%, 43%, 50%, and 57%, w.b.), three varieties (Zarfam, Opera, and Okapi), and three nitrogen fertilizer levels (250, 400, and 550 kg ha-1). The results of data analysis showed that the specific shearing energy increases and, bending stress and Young's modulus of canola stems decreased as the moisture content increased. The maximum value of the specific shearing energy was 3.94 MJ mm-2 for the Opera stems, while Zarfam with 3.27 MJ mm-2 had the minimum. The maximum value of the bending stress was 48.1 MPa for the Opera stems while Zarfam with 44.83 MPa had the minimum. The average of Young's modulus was found to be 3.80, 4.15, and 3.84 GPa for Zarfam, Okapi, and Opera varieties, respectively. The specific shearing energy decreased as the amount of nitrogen fertilizer increased. The maximum and minimum values of bending stress occurred with 400 and 550 kg ha-1 levels of nitrogen fertilizer, respectively.

Some Mechanical Properties of Safflower Stalk

General physical properties, bending stress, modulus of elasticity, compressive strength, shearing stress, and specific shearing energy were determined for safflower (Carthamus tinctorius L.) stalks. Test specimens were taken from two locations of the stalk: from the bottom and from the top region. Experiments were conducted in five different moisture contents of stalk. The bending stress decreased with increasing moisture content. The average bending stress value varied between 54.02 and 13.81 MPa. The modulus of elasticity in bending decreased with increases at the moisture content and the modulus of elasticity increased towards the top region. The average modulus of elasticity varied between 439.49- 95.62 MPa. The modulus of tangent in compressing decreased as the moisture content increased. The average tangent modulus varied between 31.39-6.35 daNmm-1. The shearing stress and the specific shearing energy increased with increasing moisture content. The maximum shearing stress and the specific shearing energy were 1.37 MPa and 94.64 mJmm-2, respectively. Both the shearing stress and specific shearing energy were found to be higher in the bottom region of the stalk.

Direct Force Measurements and Kinking under Elastic Deformation of Individual Multiwalled Boron Nitride Nanotubes

Individual multiwalled boron nitride nanotubes of different diameters (40−100 nm) were bent inside a 300 kV high-resolution transmission electron microscope (TEM) using a new fully integrated TEM−atomic force microscope (AFM) piezodriven holder under continuous recording of force−piezodisplacement curves. The tubes were gently compressed in situ (i.e., inside the electron microscope) between a piezomovable aluminum wire and a silicon cantilever. Typically, bending stress values ranging from ∼100 to ∼260 MPa, and corresponding to elastic moduli of 0.5−0.6 TPa, were estimated. Tube gross failures were absent up to very large bending angles (in excess of 115°). Extending the bending angles beyond 30−40° resulted in the elastic deformation of BN nanotubes, which proceeded through the propagation of consecutive momentary kinks. These had the effect of accumulating a bending curvature rather then uniformly curl the tube under the compression load. These kinks were found to be entirely reversible on reloading wi...

Flexural and interlaminar mechanical properties of unidirectional liquid crystalline single-polymer composites

New single-polymer composites were obtained by combining two types of wholly aromatic copolyester liquid crystalline fibres having melting points differing by about 40 °C. Vectran ® M and HS fibres were co-wounded on an open square metal frame in order to obtain a unidirectional preform with an equal volume fraction of both fibres. In a second stage, the preform was consolidated under pressure at temperatures ranging from 260 up to 285 °C. Under the selected processing conditions, one component (Vectran ® M) formed a continuous matrix while the other one (Vectran ® HS) retained its fibrous form and most of the original mechanical properties. In the longitudinal direction, the bending modulus resulted to be substantially independent of the consolidation temperature ( T c) with an average value of about 39 GPa, while the maximum stress sustained in the outer layer increased from 157 MPa, at T c = 260 up to 259 MPa, at T c = 285 °C. Concurrently, all the matrix related properties such as the transversal bending modulus, the transversal maximum stress in the outer layer, and the interlaminar shear strength (ILSS) markedly improved as the consolidation temperature rose. In particular, both the maximum transversal bending stress and ILSS values increased by a factor of 2.8 as T c increased from 260 up to 285 °C. Moreover, the consolidation temperature resulted to slightly affect the Charpy impact resistance of the investigated composites that, up to T c = 280 °C, oscillated around an average value of 79 kJ/m 2. On the other hand, the consolidation temperature markedly influenced the energy absorbing mechanisms. In fact, the ductility index showed a maximum value of 9 at T c = 265 °C and then it monotonously decreased down to a minimum value of 4.5 at T c = 285 °C.

Studies on Bending Moment of Bolt Shank Caused by Tightening of Threaded Fasteners

The bending acts on the bolt further with tension and torsion by tightening of the threaded fasteners. The bending moments of the bolt shank caused by the asymmetric shape of the screw threads and the tightening on the inclined bearing surface are examined analytically and experimentally. The value of bending stress within the bolt which produces by the asymmetric shape of the screw threads is very small. However, the maximum value of the bending moment of the bolt shank caused by the tightening on the inclined bearing surface increases proportionally to the angle of inclination. The value of that bending moment is large. The validity of the analyzed result is confirmed by some experiments. Furthermore, it is revealed that the bending moment of the bolt shank influences the torque coefficient for tightening of the threaded fasteners.

Bending and Shearing Characteristics of Sunflower Stalk Residue

Bending stress, modulus of elasticity, shearing stress and specific shearing energy were determined for sunflower (Heliantus annus L.) stalk. The bending forces were measured by a cantilever test in the field at different moisture contents and the bending stress and the modulus of elasticity were calculated from these data. For measuring the shearing forces, the stalk specimens were severed by using a computer aided cutting apparatus. The specific shearing energy was calculated by using the area under the shearing force versus displacement curve. The bending tests were conducted at four different moisture contents. The bending stress decreased as the moisture content increased. The average bending stress value varied between 37.77 and 62.09 MPa. The modulus of elasticity in bending also decreased as the moisture content and diameter of stalks increased. The average modulus of elasticity varied between 1251.28 and 2210.89 MPa. The shearing stress and the specific shearing energy were also determined at five moisture contents according to the stalk regions. The results showed that the shearing stress and the specific shearing energy increased as the moisture content increased. The maximum shearing stress and specific shearing energy were 1.07 MPa and 10.08 mJ mm(-2), respectively. Both the shearing stress and the specific shearing energy were found to be higher in the lower region of the stalk due to structural heterogeneity.

Experimental study of prefabricated funicular shell units

Prefabricated funicular shells were constructed using a stretched membrane as a mould. Forty-five shells with various rises and different types of reinforcement were loaded to failure and their behaviour in the elastic and non-linear range was investigated. The experimental values of membrane and bending stresses in the elastic range along diagonal sections of funicular shells subjected to uniform loading were calculated and compared with the results of numerical analysis. The results are generally found to be in close agreement with theory. Experimental values of vertical deflections along the longitudinal and transverse sections of the shells also compare favourably with the theory. The experimental failure and crack loads are obtained. Empirical equations expressing the relation between rise and reinforcement type with failure and crack loads are given.

Experimental study of prefabricated funicular shell units

Prefabricated funicular shells were constructed using a stretched membrane as a mould. Forty-five shells with various rises and different types of reinforcement were loaded to failure and their behaviour in the elastic and non-linear range was investigated. The experimental values of membrane and bending stresses in the elastic range along diagonal sections of funicular shells subjected to uniform loading were calculated and compared with the results of numerical analysis. The results are generally found to be in close agreement with theory. Experimental values of vertical deflections along the longitudinal and transverse sections of the shells also compare favourably with the theory. The experimental failure and crack loads are obtained. Empirical equations expressing the relation between rise and reinforcement type with failure and crack loads are given.

簡易測定法（ＩＤ法）で得られた残留応力の組織による変化―アスペクト比の異なるＡｌ２Ｏ３セラミックスの場合―

Recently, an indentation (ID) method using a Vickers hardness tester has been specified as a standard by the Society of Materials Science, Japan (JSMS-SD-4-01) as the method for practical use. This method determined a base value (KC) while measuring residual stress by the ID method. Porosity and other factors have been reported to cause problems when using the ID method on Al2O3, Si3N4 and ZrO2 as structural ceramics, a fact which motivated the establishment of this new method. The value measured by this method might change not only in response to microstructural factors such as grain size and aspect ratio, but also with different types of materials. However, this problem has received little attention to date.In this study, a prescribed bending moment was loaded on Al2O3 ceramics that differed in microstructure (grain size and aspect ratio). The bending stress value was considered to establish the level of residual stress, and was compared to the value obtained by the ID method. The variation of that relationship was examined as a function of the aspect ratio. The stress ratio φ' was defined as the ratio of the value determined by the ID method and the way that tensile stress σT or compressive stress σC varied with the aspect ratio. This alteration appears commonly in the case of tensile stress. It was thought that the origin of changing φ' (stress ratio) values was interaction across crack faces by grain bridging during cracking, which varied with the aspect ratio, making the crack propagation resistance value different in various materials.

Wave-generated fractures in river ice covers

The breakup of the ice cover in northern rivers is a brief but crucial event in the life cycle of many aquatic species and can trigger extreme ice jam events with major socio-economic impacts and significant climate change implications. An important, but vaguely understood, breakup process is the fracture of the winter ice cover by low-amplitude water waves. Previous work on this subject has been based on the assumption of an infinitely long wave propagating under an infinitely long and “edgeless” ice cover. This configuration does not account for structural constraints imposed by the proximity of an ice edge or a transverse crack. Consequently, it only furnishes approximate values of bending stresses, and tells little about the spacing of cracks that may be generated by an advancing wave, which is the only visual evidence that can identify the relevant fracture mechanism in the field. Herein, edge proximity is taken into account by making plausible simplifications to the ice response equation, and using wave forms of limited extent. It is shown that such conditions generally produce higher bending stresses than does the infinite wave/edgeless cover configuration. The distance of the peak bending stress from the edge, which defines the spacing of cracks, varies with wavelength and is less than 100 ice thicknesses or so. This is comparable to that of high-amplitude, single waves (or surges) that result from ice jam releases, but much less than fractures generated by bending on horizontal planes, caused by the meandering river plan form. Comparison of the present results with the limited available evidence indicates that wave-generated fractures occur during the passage of ice jam release surges.

INFLUENCE OF PROVENANCE VARIATION ON WOOD PROPERTIES OF TEAK FROM THE WESTERN GHAT REGION IN INDIA

The three major teak provenances of the Western Ghats in India were characterised in terms of mechanical and anatomical wood properties. Within the same age of 21-year-old plantations, teak from the North Kanara provenance, generally known to display slow growth, had the lower values of static bending (modulus of rupture and modulus of elasticity) and longitudinal compressive stresses than the Malabar provenance (Nilambur). The weaker timber of North Kanara provenance was attributed to its relatively high percentage of parenchyma and low percentage of fibres in the narrower rings, probably as an adaptation to nutrient-rich soil condition. Observations of 65-year-old plantations reveal that there was a trend for bending stiffness (modulus of elasticity) and maximum stress (modulus of rupture) of the timber to be highest towards the southernmost geographic location (Konni) within the latitudinal range of 9° to15° S with a greater percentage of cell wall (with higher lignification) despite the slower growth rate and well defined ring-porosity with wider bands of earlywood parenchyma tissue. The study thus underlines the need to recognise the provenance source of variation to explain the varied growth-structure-property relationships of teak and to utilise the Indian genetic resources to the optimum in future teak improvement programmes.

On the optimal performance of long-rod penetrators subjected to transverse accelerations

The paper deals with theoretical considerations on the conception and optimization of long-rod penetrators with regard to bending strain and penetration efficiency. In a first step we describe a method allowing to design long penetrators in such a manner that given values of bending stress and deflection are met if the rods are subjected to lateral forces. On the assumption of a constant lateral acceleration this results in rods with various dimensions; the aspect ratio remarkably does not remain constant. Then these penetrators are examined for maximum penetration efficiency while considering rods of equal energy. For the case studied the procedure results in an optimum velocity of about 2700 m/s. This demonstrates a fundamental difference in comparison to the optimization process with L/D-scaled penetrators where a much lower optimum velocity (2300 m/s) is obtained. In comparison to the reference penetrator (L/D=34, v=1800 m/s) the optimum penetrator — still at constant stress level and at an impact velocity of 2700 m/s — has of course a reduced mass, but also a reduced length and diameter showing an aspect ratio of 40. The perforation power could be increased by some 17%. On the other hand, the linearly scaled penetrator at constant energy only shows an increase of about 7% in penetration capability if the impact velocity reaches its optimum value at 2300 m/s. The optimization procedure of the energy-efficient penetration of constant-stress projectiles leads to an optimal velocity well in the hypervelocity regime. Furthermore, the special design of the penetrators with constant stress level results in a gain of penetration efficiency.

Compressive/Tensile Stresses and Lignified Cells as Resistance Components in Joints between Stem Segments of Opuntia fulgida and Opuntia versicolor (Cactaceae)

Many species of Cactaceae, a diverse group of plants with a wide variety of morphologies and reproductive strategies, have segmented stems in which terminal stem segments may be separated from main stem segments with varying amounts of resistance. Terminal stem segments that are removed with little resistance may easily form adventitious roots to produce new plants asexually, whereas other species with high resistances to stem segment removal may predominately reproduce sexually. The purposes of this study were (1) to quantitatively determine the stresses at joints between stem segments of two species of Opuntia (Opuntia fulgida [jumping cholla] and Opuntia versicolor), (2) to determine whether lignified cells of the xylem cells in joints provide the major source of resistance to these stresses, and (3) to determine whether the resistances are related to whether species reproduction is correlated with resistance stresses. The overall concept of this study is that lignified xylem tissues are the main tissue of resistance to mechanical stresses (especially tensile stress) at stem segment joints since all other tissues have relatively thin‐walled cells. This condition is analogous to reinforcing rods in concrete. The computer‐aided design package, coupled with a geometric evaluation of relative positions of stem segments, provides adequate estimates of joint‐stress parameters among stem segments. Bending stresses at joints were more than 10 times greater than any other stresses. Expressing joint stress as a function of area of lignified xylem cells is a valid way of expressing the mechanics of joint integrity. Areas of lignified xylem cells were about two times greater for tensile tissues than they were for compressive tissues, and tensile joint portions exhibited a greater percentage of lignified xylem tissues closer to the external surface. Stresses at joints as a function of area of lignified xylem cells were about four times greater for O. fulgida than for O. versicolor, and the relatively high bending stress values ($$\mathrm{mean}\,=2955$$ kPa) at joints of O. fulgida coincide with its ability to have terminal stem segments removed easily and its ability to reproduce asexually by rooted stem segments. In contrast, lower bending stress values ($$\mathrm{mean}\,=1021$$ kPa) at joints of O. versicolor coincide with its greater ability to retain stem segments and its characteristic of reproducing predominately by seeds.

The rheological performance of wet-process sprayed mortars

This paper, which reports on part of a three-year research project into wet process sprayed concrete for repair, examines the influence of rheology on the pumping and spraying of mortars. The performance of seven commercially available prepackaged repair mortars and six laboratory-designed fine mortars was examined using the Tattersall two-point and Viskomat rotational viscometers, the pressure bleed test, the slump test, a build test and a vane shear strength test. These tests were used to form a rheological audit of each mortars. The two-point apparatus was successful with low-workability mortars, and their flow resistance and torque viscosities were determine. These parameters were also obtained with the Viskomat, although problems were encountered owing to the low workability of the mortars. The pressure bleed test measured both the rate and the total volume of liquid emitted from the mixes, while the vane shear strength test provided an instantaneous reading of the shear strength of the mortars and is compared with their slump. The mortars were pumped and sprayed through a worm pump to assess their suitability and to measure their adhesion to a substrate by build thickness. This value is a measure of sprayability and is converted into values of maximum shear and bending stress, which are then compared with the workability parameters in order to determine their interrelationship.

TO THE QUESTION OF CRACK PROPAGATION IN THIN WALLED CONSTRUCTION ELEMENTS

Abstract Most analytical and experimental studies in fracture mechanics are devoted to the development of methods for material crack resistance determination in the case of mode I cracking. For mode 111 cracking there are no practical investigations. In this paper an initial investigation of bending stress (or strain) components ahead of the crack have been performed in thin-walled specimens and full-scale structural elements using holographic interferometry and strain gauging. It is shown that in many cases the values of bending stresses exceed conforming values of net stresses in structural elements.

Growth hormone is not able to counteract osteopenia of rat cortical bone induced by glucocorticoid with protracted effect.

Osteopenia and inhibited longitudinal growth in childhood are serious side effects during glucocorticoid therapy. The effects of glucocorticoids on bone have been confirmed in animal experiments. Long-term glucocorticoid administration to rats results in reduced body weights, reduced bone growth (length and cross-sectional area), and bone strength. Glucocorticoid treatment also resulted in a reduced bending stress, indicating reduced bone quality. Growth hormone, on the other hand, increased body weights, bone dimensions, and bone strength. The aim of the present study was to evaluate if growth hormone administration would have an anabolic effect on rat bone when given to animals also receiving a high dosage of glucocorticoid. Five groups of female rats, 3.5 months old, were treated as follows: (1) saline control; (2) glucocorticoid (prednisolone: Delcortol 5 mg/kg/day); (3) growth hormone (recombinant human growth hormone 5 mg/kg/day); (4) glucocorticoid and growth hormone; and (5) food restriction, consisting of restricted access to food to reduce their weight gain to match that of the glucocorticoid injected rats. After 80 days of hormone administration the animals were sacrificed. The right femur was removed and tested biomechanically in a three-point bending procedure. The left femur was used for determination of bone dimensions. Biomechanical parameters (ultimate load and ultimate stiffness) were then normalized to diaphyseal cross-sectional diameters of the femur, giving the values of ultimate bending stress and Young's modulus. administration of both hormones simultaneously could not reverse the decrease in body weights, bone length, and diameters, or the decreased bone strength induced by glucocorticoid administration. In conclusion, growth hormone cannot prevent cortical osteopenia in female rats induced by a high dose of glucocorticoid with protracted effect.

In vitro determination of the curvatures and bending strains acting on the leaflets of polyurethane trileaflet heart valves during leaflet motion.

Leaflet tears originating from the free leaflet edge and calcification around the commissural region are common modes of failure exhibited by explanted bioprosthetic trileaflet heart valves. These may be a result of the cyclic bending and high levels of curvature that affect the leaflets within these areas during normal valve operation. These high levels of curvature occur in a short time period (approximately 20 ms) during rapid leaflet opening and to a lesser degree during leaflet closure. The curvatures that occur at the free leaflet edge of two designs of polyurethane trileaflet heart valve were determined in vitro at various stages during a cardiac cycle using a high-speed video camera (1000 frames/s). Significant deformations at the free leaflet edge were observed and bending radii as low as 0.55 +/- 0.125 mm (mean +/- standard deviation) were present during leaflet opening, 0.76 +/- 0.24 mm during leaflet closure and 1.01 +/- 0.27 mm while the valve was fully open during peak systole. The values of curvature were used to determine the values of bending strain and bending stress acting at the free leaflet edge using thin shell bending theory. The calculated values of bending strain were a maximum during the leaflet flexure associated with valve opening. These high levels of bending strain, which occur for short periods of time, are likely to be an important determinant of the valve's durability. It has been shown that the method of manufacture significantly influenced the level of bending strain in the valve leaflets. Valves manufactured using a dip-casting technique resulted in open leaflet bending strains up to 31 per cent lower than valves manufactured from solvent-cast sheets of polyurethane.