Bending stress ratio

The best performance of the individual members of the drill string is obtained when the bending stress ratio of subsequent members is less than 5.5 [38]. Bending stress ratio (BSR) is defined as a ratio of the bending section moduli of two subsequent members, e.g., between the drill collar and the pipe right above it. 

The eyele bending stress seen by the diaphragm eoupling-equipped shaft ean be obtained by a rapid ratio ealeulation... 

Fig.16 S-N fatigue diagram of a bulk diglycidyl ether of bisphenol (DGEBA)/isophoron diamine (IPD) epoxy polymer giving the maximum applied stress as a function of the number of cycles to failure (three-point bending, 25 Hz, stress ratio OminMnax = 0.1) (from [53]). The two dotted lines correspond to theoretical values of the amplitude of the effective tensile stress, Acr, calculated for (a) gross slip condition and (b) under partial slip condition for an imposed displacement ( 10 xm) which corresponds to the experimental contact endurance limit at 105 cycles...

In Canada and the United States, the relationships between the 5th percentile 10-year bending stress and those in tension and compression are based on limited timber testing of the three properties but supported by years of successful experience in construction with visual stress grades of timber (ASTM, 2005J). For tension, it is assumed that the ratio of design tensile stress Ft to design bending stress Fb is 0.45 unless other test data are available for compression the ratio is assumed to be... 

The single edge specimens were loaded under three-point bending at cyclic frequency of 10 Hz, stress ratio of 0.1. The FCGR tests were carried out in the laboratory air at the temperature of 20 °C and 700 °C. Several control tests of the composites were performed at the temperature of 800 °C. Optical and scanning electronic microscopy was used for analysis of microstructure and fracture micromechanisms of the materials. 

T = tension load in outer bolt, lb n) = modular ratio, steel to concrete, use 10 Fh = allowable bending stress. p.si Fy = yield stress, psi fh = saddle splitting force, lb fa = axial stress, psi fh = bending stress, psi f = unit force, Ib/in. 

Ar = area required, base plate, in. f = ultimate 28-day strength, psi fu = bearing pressure, psi fi = equivalent bearing pressure, psi Fb = allowable bending stress, psi Ft = allowable tension stress, psi F, = allowable compression stress, psi E, = modulus of elasticity, steel, psi Ec = modulus of elasticity, concrete, psi n = modular ratio, steel-concrete n = equivalent cantilever dimension of base plate, in. Bp = allowable bearing pressure, psi Ki,2,3 = factor... 

The bend stress relaxation (BSR) technique involves forcing a fiber into a loop of radius (Rq)- After thermal exposure, a creep induced radius of curvature (Rq) is observed in the fiber at room temperature. The salient parameter of the BSR test is the BSR ratio, m = 1 -Rt/R. The higher the value of m, the more creep resistant the material. For a complete description of the BSR technique, see DiCarlo and Dutta, 1995. 

FIGURE 3-14 One-hour bend stress relaxation ratio of polymer-derived SiC fibers and other polycrystalline SiC and AI2O3 fibers. Source Reprinted from Composites Science and Technology, Volume number 51(2), J.A. DiCarlo, Creep limitations of current polycrystalline ceramic fibers, Pp. 213-222. Copyright 1994, with permission from Elsevier Science. 

FIGURE 3-21 One-hour bend stress relaxation ratio for directionally solidified eutectic YAG/alumina fibers grown by edge-defined film growth (EFG), for polycrystalline alumina-based fibers, and for c-axis sapphire fibers. Source Morscher et al., 1995. 

Gelatin sheets were analyzed by means of a dynamic-mechanical analyzer from Perkin-Elmer DMA-7. Three point bending scan were performed using a static-to-dynamic stress ratio of 110% at 1 Hz frequency and a heating rate of 5 °C/min. Samples were maintained in a conditioned room, 50% relative hiunidity and 23 °C, for 10 days before testing. 

An experimental uniaxial stress-strain relationship, determined in tension, would provide the necessary design information for ceramics and hard materials Young s modulus, Poisson s ratio and the tensile fracture strength. However, tensUe data for brittle materials are often unreliable, due to parasitic bending stresses associated with dimensional inaccuracy in machining tensile dog-bone specimens and misalignment of the specimen grips. 

The flexural creep stiffness at loading time t, S t) [or measured flexural creep stiffness, S ,(r)], is the ratio obtained by dividing the bending stress by the bending strain. 

The flexural creep compliance, D t), if needed to be determined, is the inverse of S (t), that is, the ratio obtained by dividing the bending shear by the bending stress. 

Stt = Thread tooth stress intensity, PSI Combined stress, PSI (Tx = Average longitudinal stress, PSI bending stress, PSI V = Poissons ratio (8 = Damping factor... 

Mechanical Properties. The measurement of mechanical properties is concerned with load-deformation or stress-strain relationships. Forces may be applied as tension, shear, torsion, and compression and bending. Stress is the force divided by the cross-sectional area of the sample. Strain is the change in a physical dimension of the sample divided by the original dimension. The ratio of the stress to strain is referred to the modulus. Stress maybe applied continuously or periodically at varying rates for dilferent tests. The characteristic stress-strain curve, stress relaxation, or impact behavior is very important in determining the applications and limitations of a polsrmer. 

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