Low-cycle Impact Fatigue Research Articles

Effects of low cycle impact fatigue on the residual mode II fracture energy of adhesively bonded joints

Cyclic loading exerts a profound influence on the durability of adhesively bonded joints, particularly under cyclic impact loads. Under normal cyclic loading, adhesive joints typically reach their fatigue limit when subjected to approximately 50% of their maximum static strength. However, the endurance limit is considerably lower for cyclic impact loading, sometimes even falling below 5% of the impact strength. This paper investigates the effects of low-energy cyclic impacts on the fracture energy of an end-notched flexure (ENF) joint bonded with an epoxy-based adhesive. The study includes an analysis of the static fracture energy of the ENF joints prior to subjecting them to repeated impact cycles. Additionally, certain joints were subjected to repeated impact cycles until complete crack propagation occurred. To evaluate the residual critical fracture energy of these joints, certain cyclic impact tests were interrupted, and the joints were subsequently subjected to quasi-static loading conditions. The results reveal the remarkable sensitivity of the fracture energy of adhesive joints to the impact energy level, challenging the assumption of infinite life under cyclic impacts often made in conventional fatigue tests. Stress concentration caused by cyclic impact stress waves leads to a higher density of cracks at the specimen edges. The findings are supported by numerical analysis conducted in this study. These results underscore the importance of comprehensive inspections for bonded structures exposed to low-energy cyclic impacts, as impact fatigue can significantly diminish joint strength. The fracture energy decreases as the number of impact cycles increases, indicating a cumulative effect. The findings contribute to a better understanding of the mode II fracture behavior of adhesively bonded joints under repeated impact loads and provide insights for safe design and inspection practices.

A progressive damage model to predict the shear and mixed-mode low-cycle impact fatigue life of adhesive joints using cohesive elements

A progressive damage model to predict the shear and mixed-mode low-cycle impact fatigue life of adhesive joints using cohesive elements

601 鋼製平滑材及び切欠材の低サイクル衝撃疲労強度(GS-3 衝撃,疲労,疲労設計)

601 鋼製平滑材及び切欠材の低サイクル衝撃疲労強度(GS-3 衝撃,疲労,疲労設計)

浸炭材の低サイクル衝撃疲労特性に及ぼす表層炭素濃度と硫黄含有量の影響

Effect of surface carbon and sulfur on the low cycle impact fatigue properties in carburized steels were studied by using gear impact testing machine and strain gauge. The results obtained are summarized as follows: The low cycle impact fatigue strength was especially improved by decreasing content of the surface carbon and content of sulfur. It was found that increasing the crack initiation life by decreasing content of the surface carbon, and the initial crack length shorten. Furthermore, It was explained that the crack propagation speed decreased with decreasing sulfide. The method for estimating the crack initiation life from tensile properties of carburized layer is proposed by modifying Manson's Universal Slope Method.

浸炭材の低サイクル衝撃疲労特性に及ぼす硬さプロファイルの影響

浸炭材の低サイクル衝撃疲労特性に及ぼす硬さプロファイルの影響

Effect of carbon content and density on rolling contact fatigue of a steel : J. Petersen, P, Beiss. (Aachen University of Technology, Aachen, Germany.)

An experimental investigation has been conducted to study micromechanisms of short crack initiation and propagation in a low carbon steel under low cycle impact fatigue loading. The results indicated that the most favorable site for crack nucleation was grain boundaries. On the other hand grain boundaries were the effective obstruction for short crack growth. The progressive process of crack growing across a grain boundary involved crack tip blunting, plastic flow zone forming, crack branching and only one of the branches growing continuously. Crack nucleation and propagation along slip bands were difficult in the grains with wavy or cross slip bands, and they were easy in the grains with straight slip bands. The short crack growth rate fluctuated periodically until the crack length reached a critical value and then crack growth accelerated.

Micromechanisms of fatigue crack nucleation and short crack growth in a low carbon steel under low cycle impact fatigue loading

An experimental investigation has been conducted to study micromechanisms of short crack initiation and propagation in a low carbon steel under low cycle impact fatigue loading. The results indicated that the most favorable site for crack nucleation was grain boundaries. On the other hand grain boundaries were the effective obstruction for short crack growth. The progressive process of crack growing across a grain boundary involved crack tip blunting, plastic flow zone forming, crack branching and only one of the branches growing continuously. Crack nucleation and propagation along slip bands were difficult in the grains with wavy or cross slip bands, and they were easy in the grains with straight slip bands. The short crack growth rate fluctuated periodically until the crack length reached a critical value and then crack growth accelerated.

Low-Cycle Impact Fatigue of SiC<SUB>w</SUB>/7475Al Composite

Important uses in the future for metal-matrix composites are in aerospace, weaponry, and high-speed power plants in which the inertial force produced by great acceleration is a load of high strain rate. Therefore close attention is given to the mechanical behavior of a composite at high strain rates. This paper reports a study of the behavior and mechanisms of a SiC w /7475 composite in low-cycle impact fatigue (LCIF). The LCIF and impact tension tests were conducted by using the push-pull impact fatigue apparatus developed by the authors, in which the loading assembly was actually a combination of a Hopkinson’s pressure bar and an extension bar. In the apparatus the trapezoidal stress wave loads were produced. The strain rates in specimens may reach 400 s -1 .The results show that for a SiC w /7475 composite, the strain-rate effects on yield stress, ductility, cyclic hardening and softening, δ e /2-N f relation, and transition life were slight. In low-cycle impact fatigue the cracks often initiated within or near the SiC particles, which mingled in the composite. The SiC w /7475 composite was found to be less ductile than its alloy matrix; in low-cycle fatigue brittleness appears. Therefore great attention must be given to the behavior of the composite when it is used as a structural material.

Effect of strain rate on low-cycle fatigue behaviour and mechanism of SiCp/Ly12 composite

A study has been made of the behaviour and fracture mechanism of SiCp/Ly12 composite in low-cycle impact fatigue (LCIF). The results showed that in LCIF in conditions of lower strain range-higher fatigue life, a cyclic stability, even cyclic softening, happened in the composite. In the LCIF test the fatigue life of the SiCp/Ly12 composite was sensitive to the content of SiC particles so the LCIF test is an almost unique method to distinguish small differences in ductility among these brittle materials. As the composite fractured first in the SiC particles a break, smash or interface separation occurred, then in the matrix a cavities coalescence fracture was induced. Finally it is seen that under many circumstances the SiC particles were really a weakening phase while increasing the rigidity of the composite, therefore when the composite is used as a structural material great attention must be paid to its behavior.

High strain-rate low-cycle impact fatigue of a medium-carbon alloy steel

A push-pull impact fatigue testing apparatus and relevant testing procedure designed by the authors are presented. Based on the principles of Hopkinson's bar, the specimens are subjected to trapezoidal wave loads. The strain rates in the specimens may reach 400 s −1. In this study low-cycle impact fatigue tests were carried out on quench-tempered 40Cr steel, while ordinary low-cycle fatigue tests were conducted in parallel. The results showed that there was no obvious overstress under impact loading. Reversal impact loading did not produce an apparent Bauschinger effect, which reveals a deformation mechanism different from ordinary low-cycle fatigue. The high strain rates in low-cycle impact fatigue make the steel brittle and amenable to early failure. Therefore low-cycle impact fatigue is considered more dangerous than ordinary low-cycle fatigue.

Low-cycle impact fatigue of mild steel and austenitic stainless steel

A study has been made of the low-cycle impact fatigue behaviours of low-carbon steel and austenitic stainless steel including cyclic stress-strain behaviour, cyclic hardening and fatigue life. Similarities and dissimilarities in cyclic deformation and fatigue fracture between low-cycle impact fatigue and ordinary low-cycle fatigue of the materials are discussed. This gives evidence for the presence of a considerable strain rate effect in low-cycle fatigue.

ＳＭ５０鋼の低サイクル衝撃疲労強度におよぼすイオン窒化処理の影響

Ion-nitriding treatment has been brought into greater use as a surface hardening technique, for it offers such potential advantages as saving energy, clean procedure and so forth. Though the fundamental mechanical properties of ion-nitrided specimens have been investigated from various points of view, there exist few papers on their fatigue behavior under repeated impact load. In the present study, a series of low cycle impact fatigue tests were carried out on the ion-nitrided SM50 steel specimens by using the Matsumura type impact fatigue testing machine. The results obtained at four impact energy levels of 0.2, 0.3, 0.4 and 0.5 kgf·m indicated that the surface hardened layer of the ion-nitrided specimen behaved in a brittle manner, that is, surface cracks initiated at the first impact regardless of the impact energy level. It was concluded that such brittle cracks shortened the fatigue lives of the ion-nitrided specimens, when compared with the results for the annealed SM50 specimens. Furthermore, the above mentioned fatigue properties were discussed in relation to the fracture mode in monotonic tensile tests.

Effect of plastic surface deformation on the kinetics of failure of high-strength steel in low-cycle fatigue

1. Ultrasonic strain-hardening of high-strength steel 35KhN2MFA increases its low cycle impact fatigue resistance at the stages of fatigue crack nucleation and propagation. 2. The lower the level of cyclic stresses is, the greater is the degree to which the increase of endurance of steel after USSH in impact bending is determined by the decrease of the fatigue crack growth rate. 3. Plastic surface deformation of high-strength steel increases considerably the length of the period of slow fatigue crack growth and has practically no effect on the length of the period of accelerated fatigue crack growth.

THE LOW CYCLE IMPACT FATIGUE PROPERTIES OF PEARLITIC PLAIN CARBON STEELS

AbstractThe results of Stan ton and Bairstow (1908) have been reanalyzed to yield information on the composition dependence of the low cycle impact fatigue properties of pearlitic plain carbon steels. It has been found that the energy absorbed per impact, Ei, and the number of impacts are failure, Nf, are related by the equation:In this equation q is determined by the carbon, manganese and silicon contents of the steel; Eo is the impact endurance limit; and C and D are constants. The curve represented by this equation intersects that representing the Johnson‐Keller high cycle impact fatigue equation at a value of logeNf equal to 1/C. Thus, the transition from low to high cycle impact fatigue occurs at this value of logeNf.

Effect of phase composition for nickel steel on low-cycle impact fatigue resistance

1. The optinum amount of residual austenite in the structure of nickel steel 44N14, providing the greatest resistance to impact fatigue, increases with a reduction in the level of cyclic stresses. 2. With an increase in the amount of residual austenite in the structure of nickel steel, the relative duration of the fatigue-crack initiation period also increases, and this occurs to a greater extent with a lower level of cyclic stresses.

Low-cycle impact fatigue strength of steel N18K9M5T with a biphase?+? structure

1. The stabilization of dispersed retained austenite evenly distributed in the martensitic matrix due to TCT increases the resistance of steel N18K9M5T to low-cycle impact fatigue. 2. The effect of retained austenite is due to the development of the deformational γ → α transformation in the crack tip, which promotes relaxation of stresses from the external load and increases the energy absorbed in the process of failure. 3. With increasing cyclic stresses the effect of the deformational γ → α transformation on the resistance to low-cycle impact fatigue decreases. 4. The stabilization of retained austenite in the structure of the steel during TCT is due to diffusional redistribution of alloying elements during heating and also to the small size of the crystals of γ phase. 5. TCT can be recommended to increase the structural strength of parts made of maraging steels that are subject to cyclic impact loads in operation.

Effect of Notch on Impact Fatigue Strength of Mild Steels

In order to study the effect of notch on its impact fatigue strength of mild steels, low-cycle impact fatigue tests were carried out on the specimens of 0.2% carbon steel having various circumferential notches under repeated impact tensile loads. The experimental results are summarized as follows:(1) The impact low-cycle fatigue strength σ, in the case of notched specimens, is expressed byσNfm*Tn*=D*where Nf is the life of rupture, T is the loading time and m*, n* and D* are material constants.(2) The relations of m* and n* with the stress concentration factor α are given bym*=m0αa, n*=m0αbwhere m0, a and b are experimental constants.(3) The fatigue notch factor β is related to the stress concentration factor α byβ=α-cexpm0(αa-1)lnNfwhere c is an experimental constant.

Kinetics of crack growth in maraging and medium-alloy steels during low-cycle impact fatigue tests

1. The duration of the period of crack nucleation in steels N18K9M5T and 30KhN2MFA varies little with the magnitude of cyclic stresses. 2. A period of slow crack growth is observed in steels 30KhN2MFA and N18K9M5T at σmax=165 kgf/mm2 and is characterized by fatigue microbands in the fracture-ductile in the maraging steel, brittle in the medium-carbon steel. With increasing crack length (period of accelerated crack growth) the area occupied by microbands in the fracture decreases and the percentage of dimpled fracture increases. 3. At high cyclic stresses (σmax=260 and 360 kgf/mm2) the period of slow crack growth is absent in steels 30KhN2MFA and N18K9M5T. 4. The rate of crack growth determined by the difference of electrical potentials is in satisfactory agreement with the width of fatigue microbands, particularly in the period of slow crack growth. In the period of accelerated crack growth it is somewhat higher than the width of microbands. 5. The high regularity of fatigue microbands in the fractures of steel N18K9M5T indicates greater evenness of the properties determining the resistance to fracture at high cyclic impact loads than for steel 30KhN·2MFA.

Low Cycle Impact Fatigue on Pure Aluminum

To investigate the influence of the surface layer rataining the roll effect on the low cycle impact fatigue properties of pure aluminum plate, the tensile impact fatigue tests were carried out within 100 impact blows using the two types of specimens. The specimen of the first type had the surface layer which retained the roll effect, and the specimes of the second type were fully annealed ones and were consisted of the grains of about 30μ diameter. Observations were made on the impact stress pattern and the elongation of the specimens during the tests. The surface deteriorations due to the plastic strain were also examined by means of an optical microscope and by an X-ray diffractometer. From these results, the impact fatigue behaviors of both types of specimens were compared and discussed from various view points.