Rotating Bending Fatigue Testing Machine Research Articles

√area法を用いたアルミダイカスト合金の疲労限度予測

In order to evaluate quantitatively the effects of casting defects on the fatigue properties of aluminum die-casting alloy, a fatigue limit estimation for aluminum die-casting alloy (JIS ADC12) containing large casting defects was proposed by means of √area method. Fatigue tests were performed in ambient air by means of a dual spindle type rotating bending fatigue testing machine for two types of the specimen; one is an hourglass type specimen and the other is a smooth specimen having four artificial drilled holes whose √area were ranged from 300 to 2000 μm on the surface. After fatigue tests, fracture surfaces and artificial defects were observed using an optical microscope and a scanning electron microscope (SEM). As results, all hourglass type specimens failed from casting defects. In the case of the smooth specimen having four artificial drilled holes, fatigue limit tended to decrease as artificial defects became large. According to the fatigue limits of the hourglass type specimen and of the straight type specimens having four artificial drilled holes, fatigue limit estimation for aluminum die-casting alloy was proposed by means of modified √area method. In addition, it was clarified that the proposed equations for JIS ADC12 could estimate fatigue limits of another type aluminum die-casting alloys, JIS ADC10-T6.

Design of Threaded Fatigue Test Specimen for Machining

Design and machining of the fatigue test specimens have significant effects on the duration and reliability of fatigue test. Fatigue test specimens essentially consist of three parts: the center or critical test section, which is the region where required conditions are simulated as closely as possible, and the two ends, which serve to transfer the load from the grips to the center section. When high strength materials are used for a complex geometry, such as a thread need to be tested, design and manufacturing of the specimens become more influential on the reliability and duration of the tests. Threaded fatigue test specimens were designed, machined, and tested in a four-point rotary bending fatigue testing machine. An innovative threaded fatigue test specimen that consistently fails at the critical test section was designed, machined, and tested successfully to give the required fatigue notch factor. Because of full scale fatigue testing with threaded parts is very expensive and sometimes dangerous, evaluated threaded fatigue specimen can be used in fatigue testing and it reduces duration of the experiment more than 60% for machined threaded specimens.

Effects of pretreatment and HVOF sprayed cermet coating on fatigue properties of TC21 titanium alloy

The effects of grit blasting (GB), shot peening (SP) pretreatment and high velocity oxygen fuel(HVOF) sprayed WC-17Co cermet coating on the fatigue properties of the novel ultra-high strength TC21 titanium alloy were investigated with a rotating bending fatigue test machine. The basic properties and surface integrity of the coating were investigated by using X-ray diffraction (XRD), surface roughness meter, microscopic hardness tester, scanning electron microscopy (SEM) and X-ray stress test instruments. The results showed that the residual compressive stress could be introduced into the surface of TC21 alloy by GB and SP pretreatment, and that HVOF sprayed WC-17Co coating was compactly bonded with TC21 alloy substrate and it significantly improved the surface hardness of the substrate. However, there was a certain residual tensile stress in the sublayer of the coating. SP could significantly increase fatigue resistance of TC21 alloy due to the surface residual compressive stress. There was no significant effect on fatigue resistance by GB treatment due to the offset between the influence of surface residual compressive stress and the surface notch effect. The fatigue resistance of TC21 alloy was significantly reduced by HVOF WC-17Co coating prepared with GB pretreatment. This could be attributed to the relaxation of surface residual compressive stress during the HVOF heating process, pore defects and residual tensile stress distribution in the WC-17Co coating with low toughness, and the surface notch induced by GB. The fatigue resistance of TC21 alloy was slightly reduced by HVOF WC-17Co coating prepared with SP pretreatment. This was attributed to the offset between the advantage effect by SP and disadvantageous effect of WC-17Co coating and high temperature factor during the HVOF process.

OS1301 高清浄度弁ばね鋼SWOSC-Vの超高サイクル域における内部疲労破壊メカニズムに関する研究

In order to investigate the effects of residual stress and surface roughness on very high cycle property of high cleanliness spring steel (SWOSC-V), 3 kinds of surface finished specimens (electrochemical polished, shot-peened and electrochemical polished pre-treated with shot peening) were prepared. Fatigue tests were performed using a rotating bending fatigue testing machine. Some specimens failed in interior-induced fracture mode in very high cycle regime. However, non-metallic inclusions were not observed at the crack initiation site, but singular defects were observed. The mechanism of interior-induced fatigue fracture was discussed from viewpoints of fractography by measuring slopes of the defects on the basis of observation of fracture surface.

Investigating the fretting fatigue life of thin film titanium nitride coated aerospace Al7075-T6 alloy

Application of surface modification methods is expected to be a supreme solution to diminishing fretting damage. In this study, our aim was to improve the fretting fatigue life of Al7075-T6 alloy by covering it with a TiN thin film hard coating using the magnetron sputtering technique. Coated specimens with the best surface hardness, adhesion strength and roughness were tested with a rotating bending fatigue test machine. The fatigue results indicate that fretting was significantly detrimental and reduced the fatigue life of uncoated specimens, while a slighter decrease was observed for coated samples with high surface hardness and adhesion. The fretting fatigue lives of coated specimens with high surface hardness and adhesion strength improved 61% and 16% at high bending stress and 39% and 77% at low bending stress, respectively, in comparison to the uncoated specimens. In addition, the lowest surface roughness resulting from thin film TiN coating improved the fretting fatigue life of specimens by 18% at low cyclic fatigue, while at high cyclic fatigue the result was reversed.

Evaluation of stress life of aluminum alloy using reliability based approach

In the present investigation the characteristic fatigue life prediction of A 356.2 T6 aluminum alloy has been statistically analyzed by log normal distribution. Fatigue tests were conducted on aluminum alloy specimen on rotary bending fatigue testing machine at six different stress levels. A step wise procedure is outlined to determine the number of specimen required at predetermined stress amplitudes. Details of generation of S-N curve for A 356.2 T6 aluminum alloy using a regression analysis is delineated. ANOVA is performed in order to check the significance of regression equation. The adequate sample size required for evaluating the average fatigue life of A 356.2 T6 with an acceptable error at 50 % probability and 90 % confidence level using log normal distribution is established from this study. The experimental results are presented in the form of R-S-N curves, which are helpful for designers.

FATIGUE PROPERTIES OF SUS304 STAINLESS STEEL AFTER ULTRASONIC NANOCRYSTAL SURFACE MODIFICATION (UNSM)

The changing of materials surface properties method always was taken into improving the fatigue strength. In this paper, an ultrasonic nanocrystal surface modification(UNSM) technique was used on the SUS 304 stainless steel to form a nanostructured surface layer with different static load(70N, 90N, 110N, 130N) and the vibration strike number was about 20,000times/mm2. The untreated and different condition specimens fatigue strength was all tested by a dual-spindle rotating bending fatigue test machine. SPring-8(a large synchrotron radiation facility) was used to test the surface nanocrystallization components. The X-ray diffraction (XRD), the scanning electron microscopy (SEM), optical microscope and a micro-Vickers hardness tester (MVK-E3, Akashi) were separately used to get the surface residual stresses, fracture surface after fatigue testing, metallographic structure and the microhardness of the nanostructured surface layer. The result showed that martensite transformation took place on the surface of specimens, the surface residual stresses had only a small increase and some cracks occurred between the martensite layer and the austenite layer, but the fatigue strength of 90N improved 81%.

쇼트 피닝의 압력변화에 따른 A7075-T651재의 VHCF 피로특성

In this paper, the fatigue characteristics of shot peened A7075-T651 alloy were compared with those of the specimens without the shot peening. The multi-spindle and single-spindle rotating bending fatigue testing machines were employed for the evaluation. Shot peening (SP) with various pressure (5 psi, 10 psi, 15 psi, 25 psi and 35 psi) were used in this test. In order to investigate the effect of the applied pressure during the SP, we carried out the surface roughness test, compressive residual stress test, hardness test, tensile test, VHCF (Very high cycle fatigue) test and SEM observation. SP induced the formation of remarkable compressive residual stress from the surface to certain depth of sample by means of the plastic deformation. The surface hardness and the fatigue characteristics of the specimens were also modified by the SP. According to the S-N curves, fatigue lives of shot peended sample with 25 psi measures 50 times higher than that of the untreated sample. The fatigue lives of shot peened sample with 15 psi and 35 psi measure approximately 10 times higher than that of the untreated ones.

Experiment Research on the Influence of Fretting on Crack Propagation

In order to investigate the influence of fretting induced by a shrink-fit shaft and hub subjected to rotating bending on crack propagation on different position, small specimens consisted of shaft and hub were tested on the four point rotating bending fatigue test machine. The experimental result shows that the fretting fatigue life of specimen with notch outside the shaft-hub contact is shortest, and the fretting fatigue life of specimen with notch inside the shaft-hub contact is longest.

Design of a Cantilever - Type Rotating Bending Fatigue Testing Machine

This research is centered on the design of a low–cost cantilever loading rotating bending fatigue testing machine using locally sourced materials. The design principle was based on the adaptation of the technical theory of bending of elastic beams. Design drawings were produced and components/materials selections were based on functionality, durability, cost and local availability. The major parts of the machine: the machine main frame, the rotating shaft, the bearing and the bearing housing, the specimen clamping system, pulleys, speed counter, electric motor, and dead weights; were fabricated and then assembled following the design specifications. The machine performance was evaluated using test specimens which were machined in conformity with standard procedures. It was observed that the machine has the potentials of generating reliable bending stress – number of cycles data; and the cost of design (171,000 Naira) was lower in comparison to that of rotating bending machines from abroad. Also the machine has the advantages of ease of operation and maintenance, and is safe for use.

OS0613 SCM435鋼の超高サイクル回転曲げ疲労試験におけるコーキシング効果に関する研究(OS6-3 材質および熱処理の影響,OS-6 金属材料の超高サイクル疲労と信頼性評価)

In order to investigate the coaxing effect, rotating bending fatigue tests were carried out on SCM435 steels with four different heat treatments by means of dual-spindle rotating bending fatigue testing machine. Experimental results thus obtained were quantitatively evaluated by the Miner's rule. As a result, the coaxing effect was confirmed for quenched specimen and specimens tempered at 300 ℃ under every stress changing cycles of 10^5, 10^6, 10^7 and 10^8. However, such a coxing effect was not confirmed for specimens tempered at 500℃ except for a stress changing cycles of 10^8.

OS0605 高清浄度弁ばね鋼の超高サイクル回転曲げ疲労特性に関する研究(OS6-2 内部破壊とそのメカニズム,OS-6 金属材料の超高サイクル疲労と信頼性評価)

In order to investigate the very high cycle fatigue properties of high cleanliness valve spring steel, rotating bending fatigue tests were performed by means of dual-spindle rotating bending fatigue testing machine. Fracture surfaces of failed specimens were observed by a scanning electron microscope (SEM) and fracture mechanisms of this material were discussed from view points of fractography and fracture mechanics. As results, it was found that the interior-initiated fracture would occur even for specimens without non-metallic inclusions inside the material. This fact suggests that the interior clack takes place at a certain kind of microstructural defect.

Fatigue behaviour of friction welded medium carbon steel and austenitic stainless steel dissimilar joints

This paper reports the fatigue behaviour of friction welded medium carbon steel–austenitic stainless steel (MCS–ASS) dissimilar joints. Commercial grade medium carbon steel rods of 12mm diameter and AISI 304 grade austenitic stainless steel rods of 12mm diameter were used to fabricate the joints. A constant speed, continuous drive friction welding machine was used to fabricate the joints. Fatigue life of the joints was evaluated conducting the experiments using rotary bending fatigue testing machine (R=−1). Applied stress vs. number of cycles to failure (S–N) curve was plotted for unnotched and notched specimens. Basquin constants, fatigue strength, fatigue notch factor and notch sensitivity factor were evaluated for the dissimilar joints. Fatigue strength of the joints is correlated with microstructure, microhardness and tensile properties of the joints.

FATIGUE PROPERTIES OF ALUMINUM ALLOY (A6061-T6) WITH ULTRASONIC NANO-CRYSTAL SURFACE MODIFICATION

The corrosion resistance of aluminum can be improved by adding alloy elements or using a surface heat treatment process. The machine quality can be confirmed by analyzing the surface roughness, the surface hardness and the residual stress. In this paper, the fatigue characteristics of A6061-T6 aluminum specimens were obtained and compared with those of the treated specimens with the UNSM (Ultrasonic Nano-Crystal Surface Modification) technology and the untreated ones by using a multi-spindle rotating bending fatigue testing machine. The fatigue crack initiation and fatigue lives of the treated specimens with the UNSM technology was delayed and extended by the UNSM effects that are the increase of surface hardness, and the reduction of the surface roughness.

Characterization of fretting damage in a press-fitted shaft below the fretting fatigue limit

In this paper, the characterization of contact surface damage due to fretting in a press-fitted shaft below the fretting fatigue limit is proposed by experimental methods. A series of fatigue tests and interrupted fatigue tests on the small scale press-fitted specimen were carried out by using rotating bending fatigue test machine. Macroscopic and microscopic characteristics were examined using scanning electron microscope (SEM), optical microscope or profilometer. It is found that fretting fatigue cracks were initiated even under the fatigue limit on press-fitted shafts by the fretting. The fatigue cracks of press-fitted shafts were initiated from the edge of contact surface and propagated inward in semi-elliptical shape. Furthermore, the fretting wear rates at the contact edge are increased rapidly at the initial stage of total fatigue life. After steep increasing, the increase of wear rate is nearly constant under the load condition below the fretting fatigue limit. It is thus suggested that the fretting wear must be considered on the fatigue life evaluation because the fatigue crack nucleation and propagation process is strongly related to the evolution of surface profile by fretting wear in the press-fitted structures.

Characteristics of Fretting Wear in a Press-Fitted Shaft Subjected to Bending Load

This paper presents the results of an experimental investigation of fretting wear characteristics on the contact surface of press-fitted shaft subjected to a cyclic bending load. A series of interrupted fretting wear tests with press-fitted specimens were carried out by using a rotating bending fatigue test machine. The evolution of contact surface profile of press-fitted shaft due to fretting wear were measured with a profilometer. The local wear coefficient during the running-in period is discussed from experimental results and FE analysis. It is found that the maximum depth of fretting wear by repeated slip between shaft and boss occurred at the close of contact edge at the early stage of fatigue life and the regions of worn surface are expanded to the inner side of contact edge as increasing number of fatigue cycles. The initial fretting wear rate at the early stage of fatigue life increased rapidly at all loading condition. After steep increasing, the increase of wear rate is nearly constant in the low bending load condition. The local wear coefficient in running-in period decrease dramatically at the early stage of fretting wear.

Fatigue behavior of (graded) (Ti, Al)N-coated 1Cr11Ni2W2MoV stainless steel at high temperature

The high-cycle fatigue properties of graded (Ti, Al)N- and Ti 0.7Al 0.3N-coated 1Cr11Ni2W2MoV at 500 °C have been investigated using a rotating bending fatigue testing machine. The results show that fatigue strength and life of 1Cr11Ni2W2MoV stainless steel were apparently increased by the presence of Ti 0.7Al 0.3N coating. The fatigue life and strength was also improved to some extent by the presence of the graded coating at higher stress levels (475 MPa–525 MPa). The fracture morphologies were analyzed by SEM. It is concluded that the presence of the coatings, which were well adhered and have high compressive stress, restricted plastic deformation of the substrate, thus improved the fatigue properties of the steel.

高Si硬引線の回転曲げ疲労強度に及ぼすショットピーニングの有無と微小ストレート切欠きの影響

In late years a study of advantageous high Si hard-drawn wire is pushed forward in comparison with oil tempered wires on a cost side. In this study, influence of the minute notch which gave it to rotary bending fatigue strength of the high Si hard-drawn wire and influence of the shot peening were investigated. The test bar which we gave shot peening treatment and notch to was prepared, and each hardness, residual stress, fatigue strength were investigated. A Nakamura-type rotary bending fatigue testing machine was used in fatigue test. SEM was used for fracture surface and organization evaluation. The fatigue limit of shot peening materials rose 45% in comparison with untreated material. When the linear notch of the 30 degrees〜90 degrees notch angle was given, in the case of notch angles less than 60 degrees, the fatigue limit of untreated material and the electrolytic grinding material became equal to smooth specimen. Influence of the wire drawing structure is considered as a reason.

S0305-6-1 SCM435鋼の回転曲げ疲労試験におけるコーキング効果に関する研究([S0305-6]微視組織)

In order to investigate the coaxing effect, rotating bending fatigue tests were carried out on SCM435 steels with four different heat treatments by means of dual-spindle rotating bending fatigue testing machine. Experimental results thus obtained were quantitatively evaluated by the miner's rule. As a result, coaxing effect was confirmed for T-0, T-160 and T-300 specimens. However, it is not confirmed for T-500 specimen.

Effect of alumite surface treatments on long-life fatigue behavior of a cast aluminum in rotating bending

Alumite treatment is one of surface treatments for aluminum alloy and it provides an oxide layer (Al 2O 3) on the surface by anodizing. The oxide layer is called “alumite” in Japanese industry. This method has been widely used for aluminum alloy because the alumite possesses characteristics such as high hardness, wear resistance, and electrical resistance. In order to examine the effect of alumite layer on the fatigue behavior, fatigue tests were carried out on aluminum alloy specimens with two different alumite treatments by means of a dual-spindle rotating bending fatigue testing machine. Tests were also conducted on untreated specimens for comparison. Fracture surfaces of all the failed specimens were examined in a scanning electronic microscope (SEM). Fatigue fracture mechanisms are discussed in the light of fractography and fracture mechanics. As results of fatigue tests, significant deteriorations of the fatigue strength for alumite-treated specimens having each thickness of the alumite layer were observed in comparison with the results for untreated specimen in the short life regime. However, in long-life regime of >10 7, the fatigue strength of alumite-treated specimen having 3 μm alumite layer becomes a little higher than the results for untreated specimen.