Cyclic Bending Moment Research Articles

인공발(Prosthetic Foot) 스프링용 유리섬유강화 적층재의 적층배향에 따른 층간분리거동 해석

It is considered that the application of advanced composite materials to the prostheses for the disables is important to improve their bio-mechanical performance. Particularly, energy storing foot prosthesis is mostly important to restore gait ability of the disables with low-extremity amputation since it could provide propulsion at terminal stance enhancing the disables ability to walk long distance even run and jump. Therefore, the energy storing spring of prosthetic foot keel under cyclic bending moment use mainly of high strength glass fiber reinforced plastic. The main objective of this study was to evaluate the stacking sequence effect using the delamination growth rate(dA_D/dN) of energy storing spring in glass fiber reinforced plastic under cyclic bending moment. The test results indicated that the shape of delamination zone depends on stacking sequence in GFRP laminates. Delamination area(A_D) tums out that variable types with the contour increased non-linearly toward the damage zones.

The fatigue behavior and delamination properties in fiber reinforced aramid laminates

The fuselage-wing intersection suffers from the cyclic bending moment of variable amplitude. Therefore, the influence of cyclic bending moment on the delamination and the fatigue crack propagation behavior in AFRP/ AI laminate of fuselage-wing was investigated in this study. The cyclic bending moment fatigue test in AFRP/ AI laminate was performed with five levels of bending moment. The shape and size of the delamination zone formed along the fatigue crack between aluminum sheet and aramid fiber-adhesive layer were measured by an ultrasonic C-scan. The relationships between da/dN and △K, between the cyclic bending moment and the delamination zone size, and between the fiber bridging behavior and the delamination zone were studied. As results, fiber failures were not observed in the delamination zone in this study; the fiber bridging modification factor increases and the fatigue crack growth rate decrease; and the shape of delamination zone is semi-elliptic with the contour decreasing non-linearly toward the crack tip.

층간분리성장률(dAD/da)과 섬유가교효과인자(FBE)를 이용한 Al/GFRP 적층재의 피로거동 해석

The influence of cyclic bending moment on the delamination and the fatigue crack propagation behavior in Al/GFRP laminate such as the wing section was investigated. The main objective ofbr/ this study was to evaluate the relationship between crack profile and delamination behavior. And a propose parameter on the delamination growth rate(dA_D/da) of Al/GFRP laminates with a saw-cut using relationship between delamination area(A_D) and cycles(N). crack length(a). stress intensity factor range(??K). Also. the fiber bridging effect factor(F_BE) was propose that the fiber bridging modification factor( ?? _fb) to evaluate using the delamination growth rate(dA_D/da). The shape and size of the delamination zone formed along the fatigue crack between aluminum alloy sheet. Glass fiber-adhesive layer were measured by an ultrasonic C-scan image. The shape of delamination zone turns out to be semi-elliptic with the contour decreased non-linearly toward the crack tip. It represents that relationship between crack length and delamination growth rate(dA_D/da) were interdependent by reciprocal action, therefore it's applicable present a model for the delamination growth rate(dA_D)/da) in Al/GFRP laminates.

소컷 및 원공 주위의 피로균열 형태변화와 층간분리거동 (I) - 아라미드섬유 강화 금속적층재의 경우 -

The aramid fiber reinforced metal laminates(AFRMLs) used for the wing part fair flight suffer the cyclic bending moment of variable amplitude during service. The fatigue crack propagation and delamination behavior in AFRMLs containing a saw-cut and circular hole was investigated using the average stress criterion(ASC) model. Mechanical tests were carried out using the cyclic bending moment of 4.9 N . m and delamination was observed by ultrasonic C-scan images. In case of AFRMLs containing a saw-cut fatigue crack propagated in aluminum matrix, inducing delamination. However, in case of AFRMLs containing a circular hole, delamination formed with two types under cyclic bending moment of 4.9 N . m. First, delamination formed along the fatigue crack in aluminum matrix. Second, delamination formed without any fatigue crack around the circular hole. Therefore, delamination was formed depending on the stress distribution near the circular hole.

Combined Bending and Torsional Fatigue of Woven Roving GRP

A study of biaxial fatigue of woven roving glass reinforced polyester (GRP) subjected to in-phase and out-of-phase cyclic bending and torsional moments is presented. To evaluate failure theories for this material, tests were conducted on two fiber orientations [0, 90] and [45, −45] tubes. The results showed that for [0, 90] composites the S-N curves in pure bending and in pure torsion are sufficient to predict life. For [45, −45] tubes, the value of the normal stress interaction component of the strength tensor, H12, has to be obtained. If the ratio of the global flexural stress amplitude, A, to the accompanied global shear stress, B, is less than 2, the value of H12 may be taken as presented by Tsai-Hahn theory. But, if A/B ≥ 2, the value of H12 has to be obtained from [45, −45] pure bending S-N curve, since the failure mode is a combination of interfacial shear and matrix failure. The out-of-phase loading results showed that the life of the specimens at high stress levels is less than that for the in-phase loading with the same peak values A and B.

Behaviour of steel-to-concrete connections under combined axial force and cyclic bending

Experimental study is completed on the behaviour of end-plate-type steel-to-concrete mixed connections under combined compressive normal force and cyclic bending. The main focus of the research in on the rotational stiffness of the mixed connection and its cyclic deterioration. The initial elastic stiffness is analyzed under different values of constant compressive axial forces. Interpretation and definition of rotational stiffness are introduced. The compressive axial force significantly increases the rotational stiffness, depending on the structural solution. Characteristics of the ultimate behaviour are determined under increasing cyclic bending moment and constant axial force. The tested mixed connections are classified according to strength and rigidity using the moment-rotation envelope curves. The cyclic characteristics of the moment-rotation response of the joints are analyzed. Early deterioration of the rotational stiffness is observed.

The behaviour of pressurised plain pipework subjected to simulated seismic loading

AbstractA series of simulated seismic tests have been conducted using mild steel and stainless steel plain pipe specimens. These specimens were pressurised and subjected to fully reversed cyclic bending moments at frequencies of about 5 Hz. The bending moments and surface strains on the pipe wall were monitored and are reported here. Significant ratchetting was observed which, in the case of the mild steel specimens, lead to gross swelling and eventual failure. Although ratchetting was observed in the stainless steel specimens it was not so pronounced and failure appeared to be by low cycle fatigue.

Considerations of Gravity Effects on VAWT Rotor Configurations Which Minimize Flatwise Moments and Stresses

Anticipating that composite materials will permit greater freedom when future VAWT rotor blades are configured, this paper further examines the benefits of adopting true Troposkien shapes for blades which do not use horizontal struts. Two parameters are identified which control blade geometry under combined rotational and gravitational loads. Representative zero-bending-moment shapes are calculated, both for constant mass distribution and for several new variable-mass families. The latter include one case whose mathematical solution proves remarkably simple. Steady design stresses are found to be severely affected by deviations from the ideal shape. The concept of “aerodynamic Troposkien,” which preserves zero bending moments in the presence of 1-P cyclic normal forces, is extended to account for gravity as well as inertial effects on blade shape. This concept is limited to unstalled flow and it is found to require unrealistic blade chord distributions near the tower when gravity effects are included. It is noted that both steady gravitational loads and nonsteady aerodynamic normal force loads will become increasingly important in achieving high-cycle fatigue life with larger-scale rotor blades. It is indicated that this achievement will depend primarily on configuring the rotor blades to minimize the cyclic flatwise bending moments and stresses due to the nonsteady normal forces.

ボイラ給水ポンプ軸の寿命診断用小型Ｘ線応力測定装置

Boiler feed water pump shafts are subjected to severe thrust loads and cyclic bending moments. Half-value width and residual stress measurements by X-ray diffraction methods, which are sensitive to fatigue damage, are employed for the fatigue life assessments of pump shafts. In order to establish a damage detection system, a portable, light-weight X-ray diffraction apparatus with a rotating receiving slit and X-ray detector and a small diameter X-ray tube has been developed. Consequently, the residual stress can be measured within 20 minutes which is about half the time required using a conventional apparatus. The X-ray apparatus has been installed in a system with a specially designed mechanical scanner for a pump shaft, and as a result, the fatigue damage can be automatically measured on the pump shaft surface. The system has been applied to more than 150 actual pump shafts in a factory during in-service inspections.

Energy dissipation in R.C. Beams under cyclic loadings

A reinforced concrete beam cross section subjected to unidirectional cyclic bending moment is analysed. A fracture mechanics model explains the hysteretic phenomenon which occurs when the maximum bending moment is greater than twice the bending moment of slippage or yielding of the steel reinforcement. The critical relative crack depth ξ CR above which the hysteretic phenomenon cannot occur can be determined for each value of the parameter N p , N p being a dimensionless number dependent on the mechanical and geometrical properties of the reinforced concrete beam cross section. A numerical procedure can follow the fatigue crack growth and calculate the total energy dissipation until an unstable concrete fracture phenomenon occurs.

A Comparison of Predicted Wind Turbine Blade Loads to Test Measurements

The accurate prediction of wind turbine blade loads and response is important in predicting the fatigue life of wind machines. At the SERI Wind Energy Research Center, a rotor code called FLAP (Force and Loads Analysis Program) is currently being validated by comparing predicted results to machine measurements. The FLAP code has been modified to allow the teetering degree of freedom. This paper describes these modifications and comparisons of predicted blade bending moments to test measurements. Wind tunnel data for a 1/20th scale model will be used to compare FLAP predictions for the cyclic flap-bending moments at the 33 percent spanwise station for three different wind speeds. The comparisons will be made for both rigid and teetering hubs. Currently, the FLAP code accounts for deterministic excitations such as wind shear, tower shadow, gravity, and prescribed yawing motions. Conclusions will be made regarding the code’s accuracy in predicting the cyclic bending moments.

Response of the ligamentous lumbar spine to cyclic bending loads.

The effect of a "pure" cyclic flexion bending moment on the three-dimensional load-displacement behavior of fresh ligamentous lumbar spine was investigated. The load-displacement behavior, for 11 L1-sacrum specimens, pre- and post-cyclic fatigue bending tests were quantified using a Selspot II system. A special fixture was designed to mount the specimen within the MTS system to administer "pure" cyclic flexion bending, under displacement control, for 5 hours. The testing was accomplished in a 100% humidity chamber at 0.5 Hz. The maximum cyclic bending moment, based on the literature dealing with loads experienced by the spine during activities involving lifting, was set at 3.0 Nm. An increase in motion of the order of 10% in the extension loading mode was observed. The increase in motion in other loading modes was not significant. In the extension loading mode, the increase in the anteroposterior displacement (retrodisplacement) in general was higher than the corresponding rotation component. The results suggest that the bending moment of low magnitude, usually experienced by the spine during activities of daily living, alone may not trigger the mechanical failure processes in the disc. The presence of high axial compressive loads on the disc seems to be the main contributing factor in this process. The presence of bending moments and axial twist along with axial compressive load may accelerate the unstable processes leading to low back pain.

Study of the non-uniform growth of a plane crack in a three-dimensional body subjected to non-proportional loadings

A rod with a circular section is subjected to a cyclic four-point bending moment so that a crack initiates from a circumferential V-notch and propagates in the plane of symmetry. By rotating the specimen through arbitrary angles from time to time, complicated crack front shapes are obtained. One of these complicated crack fronts, the evolution of which is experimentally observed, is modelled by using three-dimensional boundary elements. Different virtual crack extensions are simulated in which local extensions correspond to the growth of the crack front along only one element side and global extensions correspond to the uniform or non-uniform growth of the whole crack front. In each case, the strain energy release rate is calculated either from its energetic definition or from the values of the stress intensity factors. The calculations confirm the validity of the maximum energy release rate criterion to predict the crack front evolution.

Ratchetting tests of a stepped beam under steady tension and cycling bending

Seven identical stepped beams, made of a lead alloy, were loaded by steady tension and cyclic bending. Three bending moments superimposing equal hogging and sagging were used in the tests. Six different tensions were also used. After test of 15 cycles, most beams were re-loaded with a greater mean tension and the same cyclic bending moment. Strains were measured in the (circular arc) fillets at the step and in the shank. Ratchetting strains per cycle decreased during each test; steady values were estimated and related to the load magnitudes. The common use of the 0.2 per cent proof stress as the yield stress for an equivalent elastic-perfectly-plastic materials has been shown to be extremely conservative.

鋼構造溶接接合部の低サイクル疲労強度に関する実験的研究 : その 2 理想化された柱はり溶接接合部の疲労強度

In order to clarify the mechanical properties and the low-cycle fatigue strength of the idealized beam-to-column welded joints, this experimental investigation was carried out. Specimens, consisted of JIS SS 41 mild steel plates, were welded by means of CO_2-Gas butt welding or Non-Gas butt welding and fabricated to flat plate shapes which were named A-Type, or crossed shapes named B or C-Type. Three types of specimens were loaded at constant amplitudes from ±0.5% to ±1.5% as the deformations between the gauge length in a manner of quasi-static state. Only the C-Type specimens were subjected to constant bi-axial forces which simulated cyclic bending moments and column axial forces, using a special loading apparatus. The following phenomena were clearly observed from the results of the monotonic tension tests; anisotropy of the mild steel plates in the thickness direction existed and the sensitivity on Lamellar Tearing was quite high. The low-cycle fatigue strength of the A and B-Type specimens is well expressed by the well known Manson-Coffin formulae in terms of the non-dimensional elastic and plastic strain amplitudes and the equivalent fatigue lives. No deteriorations can be remarkable observed from the biaxial fatigue tests using the C-Type specimens in the nondimensional form of fatigue strength, which employed the plastic anisotropy proposed by Hill's yield criteria.

Shaft Failure of Large Axial Flow Pumps

Failure of shafts driving large axial flow pumps was found to be caused by intake flow pattern. Extensive tests on prototype pump and laboratory model were used to identify and correct the problem. Strains measured on the shaft during pump operation showed the existence of a cyclic bending moment sufficiently large to cause a fatigue failure. The bending moment was not a critical speed phenomenon and was assumed to be caused by hydraulic forces acting on the impeller. Laboratory model tests identified a vortex in the pump intake. The vortex was not centered below the pump impeller and generated an unbalanced force on impeller blades as these passed through the irregular water flow. Changing the shape of the intake eliminated the vortex and large bending moment in the shaft.

A Reference Stress Approach to Creep Bending of Straight Tubes

Reference-stress parameters, based on the Norton constitutive equation, are developed for creep bending of circular and elliptical tubes. The parameters are presented in the form of a design chart. The reference stress methods apply also to other simple constitutive equations of the power law, exponential and hyperbolic sine forms, and also to two complex equations describing creep behaviour over the entire range from primary to tertiary. In these equations the functions of stress and time are not separable and reference stress techniques provide a convenient method of evaluating stationary stress distributions and investigating the variation of these stresses with time. Aluminium alloy tubes were creep tested with cyclic uniform bending moments. Creep strains to fracture were measured by an end-rotation method. The creep behaviour of the tubes was well predicted by reference-stress cyclic tensile creep tests.

Work Bounds and Associated Deformation of Cyclically Loaded Creeping Structures

In this paper the deformations of a beam subject to cyclic bending moment and a thick-walled cylinder subject to cyclic internal pressure are investigated for an elastic/time hardening/perfectly plastic material. Bounds [1, 2] are computed on the work done by the applied loads over a cycle when the material has reached a cyclic state of stress. The bounds provide the extreme states when the cycle time is either large or small compared with a characteristic time of the material. It is found that the difference between the bounds is generally very small. This result is discussed in relation to recent work by Williams and Leckie [3].

軸圧をうける鉄筋コンクリート部材の弾塑性曲げ変形性状に関する研究 (III) : 交番繰返し曲げ : 曲げモーメント-曲率関係

In the previous papers, Part I and II, there were analyzed on the transverse moment-curvature and load-deflection relationships of reinforced concrete members subjected to constant axial load and compared with test results in the elasto-plastic range. Here, in this paper, the moment-curvature relationships and axially accumulated strains of reinforced concrete members subjected to transverse cyclic bending moment under constant axial load are presented. They are shown in Figs. 6 : (a-1) under the variation of several constant curvature amplitudes and several constant axial load ratios. It is discussed the influences of reinforceing indices β_s・p=σ_y/F_c・p of 0.10, 0.20 and 0.30 constant axial load ratios of 2/3 N_0, 1/3 N_0, 1/6 N_0 and 0 N_0, and constant curvature amplitudes upon the behaviours mentioned above. The hysteresis loops, m-ψ, show perfect elastic perfect plastic process under the axial load ratios of 2/3 N_0 and 0 N_0, S-figure process with smaller and slipped process with larger curvature amplitude under the axial load ratios of 1/3 N_0, and binary step slipped perfect elastic-perfect plastic process under the axial load ratios of 1/6 N_0. Axially accumulated strains are most remarkable under the higher axial load ratios but not so remarkable under lower axial load ratios and smaller curvature amplitudes. In the foregoing analysis, to simplyfy the calculation, it is assumed that, the concrete area of a cross section of a reinforced concrete member is divided into three parts, each of which is considered to be concentrated on the positions of the reinforcing steels in top and bottom and of the centroid cross section.

Low-endurance fatigue of an aluminium alloy and a stainless steel in plane bending at ambient and elevated temperatures

Flat uniform specimens were cyclically bent over formers. At room temperature two strain ratios were used, R = −1 and 0, i.e. reversed symmetrical and asymmetrical strains, respectively, the strain ratio being defined as the ratio of the minimum to the maximum strain in a cycle. The increase in the value of the strain ratio was found to decrease the fatigue life of the aluminium alloy and to increase it for the stainless steel. For room temperature tests and at R = −1, the bending moment at maximum strain was found to increase in the early part of the test and was then followed by a decrease until fracture occurred, whilst for R = 0 a continuous decrease occurred throughout the tests. The effect of test temperature on fatigue life was found to be considerable and throughout the tests at elevated temperature the cyclic bending moment decreased.