Loading Fatigue Tests Research Articles

Proposal of an evaluation method of equivalent fatigue load for small wind turbine blade

This study is carried out for the purpose of collecting data that is based on the evaluation of the equivalent fatigue load for a small wind turbine. The equivalent fatigue load is indicated as the method of designing load calculation in IEC 61400-2 ed.2 DLC1.1. In this study, it is performed fatigue load test for the commercial model of the small wind turbine, and it is evaluated the applicability of S-N diagram as material specification and the material factor “m” for S-N diagram model. It is cleared that S-N diagram as material specification is able to apply to the evaluation for blade fatigue load. Moreover, it is indicated experimentally the material factor “m” of 10 to a single material of G-FRP that is composed as general small wind turbine's blades. Furthermore, it is suggested the estimated method of the equivalent fatigue load by using the fatigue load function of Simplified Load Model (SLM) and it is made a trial calculation by this method.

Individual Blade Pitch Control of a Spar-Buoy Floating Wind Turbine

The spar-buoy floating wind turbine is one of the three main floating wind turbine concepts and one of the first to proceed to a full-scale prototype stage. Multiobjective linear state feedback controllers are implemented on the spar-buoy floating wind turbine with individual blade pitching (IBP). The spar-buoy's deep draft results in a low platform pitch and roll natural frequencies. The low-frequency pitch and roll modes interact with other low-frequency modes of the system (i.e., surge and sway, respectively). Therefore, the linear state-space model used for control design must include the surge and sway degrees of freedom. Furthermore, a low platform pitch natural frequency limits the effectiveness of IBP at regulating the platform pitch around the first tower fore-aft (FA) resonant frequency. Simulations using a high-fidelity model are carried out according to design load case 1.2 of the IEC-61400-3 standard for fatigue load testing under normal operating conditions. Simulation results relative to a gain-scheduled proportional-integral controller show that a multiobjective state feedback controller is able to reduce tower FA and side-side bending fatigue loads by an average of 9%. This improvement is mainly due to IBP despite its limited effectiveness around the first tower FA resonant frequency.

통신 항법용 다중대역 안테나 내장 스킨구조의 지상시험평가

This paper suggests a test and evaluation procedure of conformal load-bearing antenna structure(CLAS) for high speed military jet application. A log periodic patch type antenna was designed for multi-band communication and navigation antenna. Carbon/Glass fiber reinforced polymer was used as a structure supporting aerodynamic loads and honeycomb layer was used to improve antenna performance. Multi-layers were stacked and cured in a hot temperature oven. Gain, VSWR and polarization pattern of CLAS were measured using anechoic chamber within 0.15~2.0 GHz frequency range. Tension, shear, fatigue and impact load test were performed to evaluate structural strength of CLAS. Antenna performance test after every structural strength test was conducted to check the effect of structural test to antenna performance. After the application of new test and evaluation procedure to validate a new CLAS, a design improvement was found.

Acoustic emission signal for fatigue crack classification on reinforced concrete beam

Fatigue crack classification on reinforced concrete beam is significantly vital. Acoustic emission (AE) signals were analysed to identify the classes of reinforced concrete (RC) beam corresponding to a specific crack mode. Third point loading fatigue test was carried out based on various range of maximum fatigue loading. The classification of crack for each phase of loading allowed the identification of the cracks mode of the beam namely tensile crack and shear crack. Average frequency and RA value were computed corresponding to channel basis and located event of AE signal and used to classify fatigue crack. The relationship between average frequency and RA value indicated clear trend with respect to crack classifications. Using this relationship trend, estimation of the crack monitoring can be made.

Design and Testing of Shock Transmission Device for Bridge Protection

The design of the shock transmission unit (STU) was based on the maximum displacement, nominal load, lock up velocity and other parameters. The STU was subjected to a series of tests for checking its behavior. During the slow movement test, the resistance force is 10kN; during the simulated dynamic test, the deflection between the point of zero load and the point of maximum load is 4mm, and the deflection during the sustained load portion of the test is 5mm; during the fast movement test, the STU locked up within 1mm, the deflection from the point of lock-up to the maximum test load is 5mm, and the stiffness of STU throughout the force range from lock-up to maximum test load in tension and compression is 7.72% and 3.6% respectively. During the overload test and the fatigue load test, the STU shows no sign of leakage or binding.

Fatigue Stiffness Analysis of Corroded RC Beams

In order to study the influence on RC beam fatigue stiffness with different corrosion rates, fatigue load tests have been taken on a set of different corrosion ratios, and the changes in stiffness to the related beams also been calculated based on the deflection of the test beams. And then, the corresponding test analysis is achieved. The results show that: the rate of increase to the deflection of specimen tends to increase and stiffness drastically reduces with the increase in the extent of corrosion under fatigue loads.

Experimental Research on Residual Strength of Concrete under Fatigue Loading and Corrosion of Magnesium Nitrate

At Present, stress corrosion and corrosion fatigue causing durability degradation of concrete structure in the field of civil engineering become an important problem,and thus become a hot topic to study. But the research on it at home and abroad is still in stage of theoretical exploration. This paper using self-designed corrosion fatigue loading test device, studied in magnesium nitrate solution of concrete under the action of erosion strength increasing regularity, results show that the concrete strength by corrosion fatigue than fatigue specimen attenuation extent.

Impact of Repeat Overweight Truck Traffic on Buried Utility Facilities

Increasing overweight truck traffic, as evident by a rapid increase of permits issued for such traffic in Texas, tends to accelerate the deterioration of pavement structural integrity. However, it is less known to what degree buried utility facilities along and across the right-of-way are affected by these overweight loads, especially if these facilities are aged or placed under an exception to the Texas Utility Accommodation Rules (UAR). In this study, researchers evaluated the damage potential of buried pipe subjected to repeat overweight traffic loads. Based on a review of technical design and engineering requirements for utility accommodation in Texas, a large-scale laboratory test was conducted to investigate fatigue behavior of polyvinyl chloride (PVC) and concrete pipe. The result of both static and fatigue load tests indicated that pipe deformation in terms of vertical diameter reduction was less than 5% of pipe diameter, the maximum allowable value. However, fatigue damage was observed for the concrete pipe even though the deformation level was very minimal. A sensitivity analysis based on the finite-element method was conducted to validate the findings of the laboratory test. The study concludes that the current UAR appear adequate with respect to the likelihood of fatigue damage to buried pipes attributable to repeat overweight loads.

Static Fatigue Experimental Research on Orthotropic Deck with Composite Pavement Layer

The experimental results show that the deck of the bridge displays obviously orthotropic features; shear nails with reasonable density can increase the binding capability of each part of deck pavement and overall mechanical performance. The results of fatigue test on the two groups of specimen indicate that the composite deck pavement added with the shear nails and the transition layer of steel fiber concrete has no sign of fatigue failure after 8.3 million fatigue loading tests, and its fatigue resisting property is obviously better than the deck pavement where the asphalt concrete is directly paved on the surface of deck, that is to say the service life of the deck pavement can be extended by the use of steel fiber concrete layer.

J056035 小形風車ブレード試験による等価疲労荷重評価(〔J056-03〕再生可能エネルギー(風力発電)(3))

This study is carried out for the purpose of collecting data that is based on the evaluation of the equivalent fatigue load for a small wind turbine. The equivalent fatigue load is indicated as the method of designing load calculation in IEC 61400-2 ed.2 DLC1.1. In this study, it is performed fatigue load test for the commercial model of the small wind turbine, and it is evaluated the applicability of S-N curve as material specification and estimated the material factor "m" for S-N curve model. It is cleared that S-N curve as material specification is able to apply to the evaluation for blade fatigue load. Furthermore, it is able to estimate the material factor "m" of 10 to a single material of G-FRP that is composed as general small wind turbine's blades. Furthermore, it is suggested the estimated method of the equivalent fatigue load by using SLM fatigue load function and it is made a trial calculation by this method.

Inclusion size evaluation and fatigue strength analysis of 35CrMo alloy railway axle steel

The axial loading fatigue tests of 35CrMo alloy railway axle steel were carried out with the untreated specimens and those treated by nitrocarburization. It is found that the untreated 35CrMo steel specimens fracture from surface, while those of the treated specimens fracture from internal inclusions. In order to investigate the inclusion size in the material, the ultrasonic fatigue tests were conducted for the 35CrMo steel by applying large risk volume specimens with straight section after nitrocarburization. The results show that the cracks of all the specimens initiate from the internal inclusion. The statistics of extreme values (SEV) method was applied to evaluate the maximum inclusion size in the large volume material and the full-scale axle. Based on the evaluated maximum inclusion sizes and the fracture mechanics, different fracture behaviors of axial loading specimens and full-scale axle as well as the effect of inclusion size on fatigue strength of full-scale axles were analyzed based on the fracture mechanics.

Fatigue damage in GFRP

PurposeComposite materials are increasingly used in the structural and mechanical fields, thanks to their high strength‐to‐weight ratios and the possibility of tailoring them to meet specific requirements. This study is focused on the damage to a glass fiber reinforced composite under different loading conditions. The aim is to find, by coupling mechanical tests with thermal analyses, a damage parameter, able to define the damage initiation in the studied material.Design/methodology/approachThe object of this work is a glass‐fiber reinforced plastic (GFRP) laminate. To study the damage of this material under different loading conditions, static, dynamic and fatigue tests were carried out. During these tests, the surface temperature of the specimens was monitored by means of an IR‐camera. In the dynamic tests, a D‐mode (dissipation mode) analysis was also performed allowing the dissipated energy to be determined.FindingsIn the literature, thermography is an experimental technique which has always been applied to the study of homogeneous materials. Results obtained from the proposed experimental tests on this GFRP composite show how this practice can be applied also to this kinds of materials, to identify their damage initiation. From these observations, the results can be used to definite a stress corresponding to the damage initiation, which can be related to the fatigue behavior, and useful in design stage with these materials.Originality/valueThis paper provides for a useful tool to understand and predict fatigue behavior of a GFRP composite, from thermographic observations. Applications of thermography to the study of composite materials is an innovative research field, and the presented results seems satisfactory and promising for further experimental investigations.

New Structural Joint by Rebar Looping Applied to Segmental Bridge Construction: Fatigue Strength Tests

The objective of this research has been to design, develop, and evaluate experimentally a modified type of construction joint of limited length between concrete slab segments. The design concept is based on an anchorage hook of reduced development length stiffened by transverse reinforcement bars. The purpose of this paper is to investigate the mechanical behavior of the joint in terms of stiffness and strength for an application that requires high durability, which often leads to serviceability problems such as cracking and water leakage at transverse joints. This can regularly appear in bridges. Additionally, bridge decks are structures that are subjected to repeated loading such as traffic loads, making it necessary to evaluate the behavior of joints under fatigue load. Therefore, studies focusing on the strength, stiffness, and serviceability of the joints must be carried out. This paper investigates experimentally the fatigue behavior and strength of loop joints with regard to the loop bar diameter, loop joint width, and applied load ranges. These results were compared with the behavior of RC slabs without joints. A total of eight slabs were fabricated for fatigue loading tests, and the failures of the different specimens (with loop joints and without) were obtained. From the test results, the mechanical behavior of the slabs with loop joints was confirmed to be similar to that of the slabs without joints. The experimental loop joint design was found to perform correctly under fatigue loads.

내화패널이 부착된 프리캐스트 PSC 풍도슬래브의 정적/동적하중에 관한 실험연구

In the longway tunnel and underground traffic road, the structure of transverse ventilation system is constructed by the airpit slab. In this study, the full scale specimens of the PSC airpit slab that attached fire resistance panel are performed the static and dynamic loading tests for evaluation of bending capacity. The first of all, it confirmed the evaluations about the fundamental efficiency of the fire resistance panel and PSC slab by the 3-point bending test and pull-off test. The tests are performed for evaluation of the bending resistance under ultimate static load and the bonded capacity under dynamic fatigue load. A fatigue test is performed for an investigation of the effect on wind pressure that is developed by transit of traffic. The damage or debonding on surface between fire resistance panel and PSC slab was not developed in dynamic fatigue load test, also the behavior of the specimens is very stable and the debonding of the fire resistance panel attached at the bottom surface of PSC slab was not developed in static load test, too. Therefore, the crack or debonding of the fire resistance panel will be not developed by external loads during the construction or completion of the precast fire resistance system.

Effect of inclusion on high cycle fatigue response of a powder metallurgy tool steel

The high cycle fatigue response of a high V-alloyed powder metallurgy tool steel (AISI 11) with different inclusion sizes was studied. Two materials of this grade at a similar hardness of about HRC 60 were subjected to axial loading fatigue tests, tensile tests and fracture toughness measurements to investigate their mechanical properties. Large inclusion above 70 μm is indicated to be responsible for the tensile fracture which happens before yielding. The fatigue strength obtained up to 107 cycles is found to decrease from approximately 1 538 MPa to 1000 MPa with the inclusion size increasing above 30 μm. The internally induced crack initiation is mainly attributed to the surface compressive residual stress of 300–450 MPa. Fractographic evaluation demonstrates that the crack initiation and propagation controlling factors of the two materials are almost the same, indicating that the two factors would be insignificantly affected by the inclusion size level. Paris sizes of the two materials both show a tendency to decrease as the ratio of stress intensity factor of crack origin to factor of fish-eye increases. The investigation into the relationship between stress intensity factors and fatigue life of the two materials further indicates that the high cycle fatigue behavior of AISI 11 is controlled by crack propagation.

PS 강봉으로 일체화된 강합성 라멘교의 거더-교대 접합부에 대한 피로 성능 평가

Integral and rigid frame bridges have advantages in bridge maintenance and structural efficiency by eliminating expansion joints and bridge supports. However, the detail of typical girder-abutment connection is rather complex and increases construction cost depending on construction detail. For the purpose of compensating disadvantages such as complexity and additional cost, a new type of bridge is proposed in this study, which improves the efficiency of construction by simplifying the construction detail of girder-abutment connection. The proposed bridge has the connection detail of steel girder and abutment integrated by prestressed PS bar installed in the connection. In this study, finite element analysis and fatigue load test are conducted to evaluate the fatigue capacity of the proposed girder-abutment connection. The results of the finite element analysis revealed that the possibility of the fatigue damage in the girder-abutment connection is very low. The results of the fatigue load test verified that the integrity of the girder and abutment connection is maintained after 2,000,000 cycles of fatigue loading.

Performance of a scaled FRP deck-on-steel girder bridge model with partial degree of composite action

The applications of FRP decks have been increasingly implemented in the United States since the mid-1990s. Although extensive research has been conducted on stiffness and strength evaluations of various types of FRP decks, studies on FRP deck-on-steel girder systems are limited. The performance of the FRP deck-on-steel girder system depends substantially on the connectors used. Recently, a prototype shear connector was developed and its advantages were illustrated through both laboratory study and field applications, where partial degree of composite action could be achieved between the deck and stringers. This paper aims to study the effectiveness of the shear connector at bridge-system level, including the static and fatigue performance of the shear connector and the bridge system, the degree of composite action of the system; and more importantly, the influence of the partial degree of composite action on load distribution factor and effective flange width since no provision is provided in AASHTO Specifications. For this purpose, a 1:3 scaled FRP deck bridge model was tested, with an FRP sandwich honeycomb deck connected to steel girders using the prototype shear connector. The test program consisted of three phases: Phase I and Phase II included static and fatigue load tests on the scaled bridge model. In Phase III, a T-section was cut-out from the bridge model and then loaded under three-point bending until failure. A Finite Element model was constructed to simulate the tests. It was shown that the shear connection was able to provide partial composite action of about 25%, and sustain a cyclic fatigue loading equivalent to 75year bridge service life span. It is shown that AASHTO Specifications can still be applicable for load distribution factor, while the effective flange width needs to be re-defined for bridge-system with partial degree of composite action. The findings from this paper can be used for design purposes.

OS1601 展伸マグネシウム合金の超高サイクル疲労強度特性に及ぼす応力比の影響

To discuss an effect of stress ratio on very high cycle fatigue properties of the extruded magnesium alloys, axial loading fatigue tests have been performed under three conditions of stress ratio, R, of 0, -1 and -1.5 in laboratory air at room temperature using hourglass shaped specimen of three kind of alloys. Specimens tested under R=-1 and -1.5 showed a step-wise S-N curve on which two knees appear while under the test of R=0 clear fatigue limit existed on the S-N diagram. From the detail observation of fracture surface, It is suggested that fatigue crack initiation mechanism changed from the twin-induced failure mode at high stress amplitude level to the slip-induced one at low stress amplitude level. This transition was occurred by the relation between the minimum stress during a cycle and the compressive yield stress at which deformation twin occurred. The deformation twin is formed during fatigue process when the minimum stress exceeds the yield stress in compression that is smaller than that in tension.

G040033 590MPa級自動車用鋼板を毋材とするスポット溶接継手の局所ひずみ挙動に基づく累積疲労損傷評価手法の検討

To establish the fatigue life evaluation method on the spot welded joints under the practical circumstance, random loading fatigue tests were conducted for the joints using a 590 MPa-class automobile base metal. In this study, the fatigue life of the spot welded joints was evaluated using two approaches, which are the external loading and local strain approaches. In the external loading approach, the cumulative damage value satisfied the standard of the automobile industry using the modified fatigue life curve considered with the mean load effect. On the other hand, the cumulative damage value was improved with approximately 20% in maximum compared with the result of the external approach in the case of the local strain approach. To investigate the relationship between the local strain behavior on the surface and near the edge of the slit, the validity of the proposed method should be clarified in future.

Establishment of the Fatigue Cumulative Damage Evaluation Based on the Applied Load for the Spot Welded Joints Using 590 MPa-Class Automobile Steel

In this paper, fatigue tests were carried out under the repeated two-step and random loading condition using the spot welded joints which had the base metal categorized into 590MPa class in order to consider the effect of their loading condition on fatigue characteristics of the joints. As the results of fatigue tests under the repeated two-step loading condition, it was found that the fatigue limit of the spot welded joints was vanished. Therefore, we found that it was necessary to consider the effect of the damage caused by the loading below the fatigue limit on the fatigue damage of the spot welded joints. When the random loading fatigue tests were carried out, it was confirmed that evaluation of the cumulative damage value considered with the mean loading effect had validity though the result of them considered without it indicated the un-conservative estimation. Thus, it was necessary to estimate the mean loading effect on the cumulative damage value of the spot welded joints under the random loading condition. Moreover, for considering the local mean stress involved with the deformation of the spot welded joints, it will be achieved to make the precise cumulative damage value evaluation.