Cyclic Stress Response Behavior Research Articles

Cyclic Fatigue Fracture Behavior of Spray-Deposited SiCp/Al-Si Composite

The cyclic fatigue characteristics of spray-deposited SiCp/Al-Si composite were investigated in comparison with the unreinforced Al-Si alloy. The as-extruded specimens were cyclically deformed with fully reversed loading under a range of total strain amplitudes. The results show that the cyclic response characteristics for the reinforced and unreinforced materials are similar to each other. Both the composite and matrix alloys display cyclic hardening under total strain amplitude of 0.35-0.5%. Otherwise, the composite exhibits higher degree of strain hardening than that of the matrix alloy. Dislocation substructure developed during cyclic deformation was analyzed using transmission electron microscopy. The discrepancy between dislocation substructures obtained from processing compared to its development during cyclic strain loading is thought to give rise to the observed cyclic stress response behavior. Fractographic analysis shows that particle/matrix debonding and particle cracking are the main mechanisms of failure in the SiC particle-reinforced composite.

Cyclic Strain Resistance, Stress Response, Fatigue Life, and Fracture Behavior of High Strength Low Alloy Steel 300 M

The focus of this technical manuscript is a record of the specific role of microstructure and test specimen orientation on cyclic stress response, cyclic strain resistance, and cyclic stress versus strain response, deformation and fracture behavior of alloy steel 300 M. The cyclic strain amplitude-controlled fatigue properties of this ultra-high strength alloy steel revealed a linear trend for the variation of log elastic strain amplitude with log reversals-to-failure, and log plastic strain amplitude with log reversals-to-failure for both longitudinal and transverse orientations. Test specimens of the longitudinal orientation showed only a marginal improvement over the transverse orientation at equivalent values of plastic strain amplitude. Cyclic stress response revealed a combination of initial hardening for the first few cycles followed by gradual softening for a large portion of fatigue life before culminating in rapid softening prior to catastrophic failure by fracture. Fracture characteristics of test specimens of this alloy steel were different at both the macroscopic and fine microscopic levels over the entire range of cyclic strain amplitudes examined. Both macroscopic and fine microscopic observations revealed fracture to be a combination of both brittle and ductile mechanisms. The underlying mechanisms governing stress response, deformation characteristics, fatigue life, and final fracture behavior are presented and discussed in light of the competing and mutually interactive influences of test specimen orientation, intrinsic microstructural effects, deformation characteristics of the microstructural constituents, cyclic strain amplitude, and response stress.

Influence of microstructure on strain-controlled fatigue and fracture behavior of ultra high strength alloy steel AerMet 100

In this paper, the results of a study aimed at understanding the specific role of microstructure on cyclic stress response, cyclic strain resistance, and cyclic stress versus strain response, deformation and fracture behavior of high strength alloy steel AerMet® 100 is presented and discussed. The cyclic strain amplitude-controlled fatigue properties of this ultra-high strength alloy steel revealed a linear trend for the variation of log elastic strain amplitude with log reversals-to-failure, and log plastic strain amplitude with log reversals-to-failure. Cyclic stress response revealed a combination of initial hardening for the first few cycles followed by stability for large portion of fatigue life before culminating in rapid softening to failure at the lower cyclic strain amplitudes and intermediate cyclic strain amplitudes and resultant enhanced cyclic fatigue life. Fracture characteristics of test specimens of this high strength alloy steel were different at both the macroscopic and fine microscopic levels over the entire range of cyclic strain amplitudes examined. Both macroscopic and fine microscopic observations revealed fracture to be essentially ductile with features reminiscent of locally occurring ductile mechanisms. The intrinsic microscopic mechanisms governing stress response, deformation characteristics, fatigue life and final fracture behavior are presented and discussed in light of the competing and mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the microstructural constituents, cyclic strain amplitude and concomitant response stress.

Low Cycle Fatigue Properties of Alloy 617 base Metal and Weld Joint at Room Temperature

Alloy 617 is the one of the leading candidate materials for intermediate heat exchangers (IHX) of a Very High Temperature Reactor (VHTR). System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. As a series of the work to better understand the LCF properties of Alloy 617 weld joints at high temperature, firstly, in this work, strain-controlled LCF testing of Alloy 617 base metal (BM) and weld joint (WJ) by a gas tungsten arc weld process (GTAW) were carried out. Fully reserved total-strain controlled LCF tests have been conducted at room temperature with four total strain ranges of 1.5, 1.2, 0.9, and 0.6%. For the LCF tests triangular test waveforms with a frequency of 0.25Hz were applied. The present paper is to characterize the LCF properties for Alloy 617 base metal (BM) and weld joint (WJ) from the cyclic stress response behavior and fatigue fracture behavior, with the comparative method. The cyclic stress response behavior was influenced by the level of total strain ranges and the material properties. Though base metal (BM) had shown higher plastic strain accumulation, the observed fatigue life of the weld joint (WJ) is lower than the base metal (BM). Coffin-Manson relationship and energy-life models can be used to determine the fatigue life.

Effect of Temperature and Strain Amplitude on Fatigue Behaviour of BCC Iron Single Crystal using Molecular Dynamics Simulation

Abstract Fatigue simulations on single crystal bcc iron have been carried out by using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) package. Finnis-Sinclair potential suitable for bcc iron has been chosen to desc ibe the interatomic interactions. Fatigue simulation was carried out at 573 K by employing fully reversed, total strain controlled cycling at various strain amplitudes in the range of ± 7% to ± 10%. From the simulation results, effect of cyclic strain amplitude on cyclic stress response and cyclic stress-strain behaviour has been determined. The development of fatigue damage with successive number of cycles using Atom Eye software has been examined.

Isothermal and thermomechanical fatigue studies on a modified 9Cr–1Mo ferritic martensitic steel

In-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) tests were carried out on a modified 9Cr–1Mo ferritic martensitic steel under a mechanical strain control mode employing a strain amplitude of ±0.4%. Different temperature ranges in the interval, 573–923K were employed for the tests which were carried out using a constant strain rate of 1.2×10−4s−1. Isothermal low cycle fatigue tests were also performed concurrently at the maximum temperatures (Tmax) of TMF tests on similar specimens and employing the same strain amplitude and strain rate. The life variation was seen to follow the sequence: IF<OP TMF<IP TMF. However, the difference in lives narrowed down with an increase in the Tmax of TMF/test temperature of IF cycling. The cyclic stress response behaviour of the alloy was characterized by a continuous softening under all testing conditions. The lower lives observed under OP TMF in comparison with IP cycling was attributed to a combined influence of oxide cracking and a higher tensile hysteresis loop energy in the former. Cyclic life under IP TMF was observed to reduce more drastically compared to OP cycling with increase in Tmax, owing to the increasing prominence of dynamic recovery effects coupled with creep deformation. Transmission electron microscopy (TEM) investigations revealed that IF cycling at the Tmax resulted in a significantly greater substructural recovery compared to that produced by TMF cycling as a consequence of which, the former led to lower lives compared to both the IP and OP TMF. Dynamic strain ageing (DSA) associated with serrated flow was observed as the deformation temperature under TMF cycling traversed the regime of 300–400°C.

Fatigue Behavior of Cast Steel ZG20SiMn under Stain Control Mode

Abstract: The fatigue behavior of cast steel ZG20SiMn under strain control mode was investigated, and the influence of imposed total strain amplitude on the cyclic deformation and fracture behavior of the cast steel ZG20SiMn was determined. The experimental results reveal that during fatigue deformation, the cast steel ZG20SiMn may exhibit the cyclic strain hardening and stable cyclic stress response behavior, which mainly depends on the imposed total strain amplitude. The relationship between plastic and elastic strain amplitudes with reversals to failure shows a single linear behavior, and can be well described by the Coffin-Manson and Basquin equations, respectively. At different total strain amplitudes, the fatigue cracks initiate at the free surface of fatigue specimens and propagate for the cast steel ZG20SiMn.

Influence of Heat Treatment on Low-Cycle Fatigue Behavior of AZ61 Magnesium Alloy

In order to identify the influence of solid solution, aging and solid solution plus aging treatments on the low-cycle fatigue behavior of the extruded AZ61 magnesium alloy, the low-cycle fatigue tests were performed at room temperature for the extruded AZ61 magnesium alloy with different treating states. The results indicate that the cyclic stress response behavior of the extruded AZ61 magnesium alloy exhibits both cyclic strain hardening and stability. The solid solution, aging and solid solution plus aging treatments tend to decrease the cyclic deformation resistance of the extruded AZ61 alloy in most conditions. The solid solution treatment can enhance the fatigue lives of the extruded AZ61 alloy at medium total strain amplitudes. In addition, the aging treatment can prolong the low-cycle fatigue lives of the AZ61 alloy at most total strain amplitudes, while the case for the solid solution plus aging treatment is just contrary. For the extruded AZ61 alloy with different treating states, a linear relationship between cyclic stress amplitude and plastic strain amplitude is noted.

A comparative study of isothermal and thermomechanical fatigue on type 316L(N) austenitic stainless steel

Thermomechanical fatigue (TMF) behaviour of a nitrogen-alloyed type 316L austenitic stainless steel under in-phase (IP) and out-of-phase (OP) cycling conditions in different temperature domains has been reported. Tests were performed under mechanical strain control mode, at a fixed strain rate of 6.4 × 10 −5 s −1 and a strain amplitude of ±0.4%. It was observed that OP TMF yielded lower lives compared to IP TMF in the sub-creep regimes, whereas the reverse was found true in the creep temperature domain. The variations observed in cyclic lives and the cyclic stress response behaviour under isothermal and TMF were examined in relation to the dynamic strain ageing (DSA) effects occurring in the intermediate temperature ranges. The development of dislocation substructures under TMF cycling was evaluated and discussed in relation to the DSA and creep processes. Extensive carbide precipitation was observed under TMF cycling that contributed to an enhanced stress response compared to isothermal cycling at the peak temperature.

Stress-Amplitude-Dependent Deformation Characteristics and Microstructures of Cyclically Stressed Ultrafine-Grained Copper

Various mechanical behaviors of ultrafine-grained (UFG) materials produced by equal channel angular pressing (ECAP) generally exhibit distinctive characteristics from those of conventional grained materials, so that the relevant studies have received sustained attention in recent years. Apparently, the understanding of the fatigue properties (among various mechanical properties) of such UFG materials is of particular importance for their practical engineering applications, many investigators have thus been attempting to explore the fatigue deformation mechanisms of UFG materials, especially of UFG copper, with different emphases. It is now commonly recognized that the low-cycle fatigue damage in UFG materials primarily results from the formation of shear bands (SBs), which can extend over far larger scales than the initial grain size, and that the cyclic softening phenomenon as well as the deterioration in fatigue life under strain-amplitude-controlled tests in the low-cycle fatigue (LCF) regime is attributed to grain coarsening due to instabilities of the ECAPed structures during cycling. On the contrary, the fatigue life of UFG materials obtained under stress-controlled tests in the highcycle fatigue (HCF) regime is normally enhanced greatly as compared to their conventional counterparts. However, the details about cyclic deformation microstructures and shear band features in LCF and HCF regimes, respectively, are less understood so far. To further understand the possibly different fatigue deformation mechanisms of UFG copper in LCF and HCF regimes, the present contribution is to report the effect of the applied stress amplitude on the cyclic stress response behavior, surface damage features as well as relevant microstructural changes of such UFG copper materials. The applied stress amplitudes ranging from 100 MPa to 200 MPa are adopted to ensure that fatigue tests are carried out within both LCF and HCF regimes.

Microstructure Variation and Hardness Diminution During Low Cycle Fatigue of 55NiCrMoV7 Steel

The influence of temperature and hardness level on the cyclic behavior of 55NiCrMoV7 steel, and the microstructure variation and hardness diminution during low cycle fatigue behavior were investigated. By means of SEM and XRD, the modality of carbides and the full-width half-maximum (FWHM) of martensite (211) [M(211)] of X-ray diffraction spectrum in fatigue specimen were studied. The results showed that the cyclic stress response behavior generally showed an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. The fatigue behavior of the steel is closely related to the hardness level. The hardness diminution and the variation of half-width M(211) are remarkably influenced by the interaction between the cyclic plastic deformation and the thermal loading when the fatigue temperature exceeds the tempering temperature of the steel.

Low-cycle fatigue behavior of in situ TiB2/Cu composite prepared by reactive hot pressing

Copper-based composite reinforced with in situ TiB2 particulates was prepared through reactive hot pressing of Ti, B and Cu powders. The formation of in situ TiB2 particulates was verified by the X-ray diffraction technique. Tensile test showed that fine TiB2 particulates were very effective to increase the tensile and yield strengths of copper at the expense of tensile ductility. Strain-controlled low-cycle fatigue measurements demonstrated that the in situ TiB2/Cu composite exhibited essentially stable cyclic stress response behavior under small total strain amplitudes of 0.1–0.3%. However, this composite exhibited slight cyclic hardening under strain amplitude of 0.4%. Such cyclic hardening was more pronounced at a total strain amplitude to 0.6% due to the formation of dislocation cells and networks. Finally, the fatigue life data of the in situ TiB2/Cu composite can be described by the Coffin–Manson equation.

Influence of hold time on cyclic stress response and fracture behavior of an Al–Mg–Si alloy

Influence of hold time on cyclic stress response and fracture behavior of an Al–Mg–Si alloy

High-temperature low-cycle fatigue behavior of K40S cobalt-base superalloy

An investigation was made on the strain-controlled low-cycle fatigue (LCF) of K40S cobalt-base superalloy at 900 °C in ambient atmosphere. The results show that K40S alloy possesses high LCF resistance in comparison with X-40 alloy. Under the testing conditions in this study, K40S alloy exhibits a cyclic stress response of initial hardening followed by softening. The cyclic stress response behavior has been attributed to dislocation-dislocation interactions and dislocation-precipitate interactions. The high response stress can lead to a large stress concentration at locations where inelastic strains of high amplitude accumulate, which account for the decreasing fatigue life with increasing strain rate. The well-distributed carbide particles are the “secondary” crack initiation sites. The secondary crack initiation relaxes the stress concentration at the crack tip, reducing the driving force of crack propagation. High-temperature LCF failure of K40S alloy results from the interaction of the mechanical fatigue and environmental oxidation.

On the low cycle fatigue deformation of K40S cobalt-base superalloy at elevated temperature

Low cycle isothermal mechanical fatigue testing K40S cobalt-base superalloy was carried out at 700 and 900 °C with total strain amplitude from ±0.1 to ±1.0 pct. Correlations between microscopic cyclic deformation and cycle stress response with various microstructural phenomena were enabled through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), detailing the deformation substructure and carbide precipitation. The results show that K40S superalloy exhibited cyclic stress response of cyclic hardening at 700 °C, and of initial hardening followed by softening at 900 °C. In addition, at both temperatures, cyclic hardening during cycle deformation increased with increasing strain amplitude, while the fatigue lifetime decreased. The cyclic stress response behavior can be rationalized based on the mechanisms associated with dislocation–dislocation interactions, dislocation–precipitate (M 23C 6) interactions and interactions between solute atoms and dislocations.

Influence of temperature on the low cycle fatigue behaviour of a modified 9Cr–1Mo ferritic steel

Low cycle fatigue (LCF) behaviour of a modified 9Cr–1Mo steel under normalized and tempered conditions is reported. The alloy was normalized at 1313K for 1 h followed by tempering at 1033K for 1 h, which resulted in a tempered martensitic structure. Total axial strain controlled LCF tests were conducted at a constant strain rate of 3×10 −3 s −1 at different strain amplitudes varying from ±0.25 to ±1.0% in the temperature range of 300–873K. The cyclic stress response behaviour, in general, showed an initial brief hardening for the first few cycles, followed by a continuous and gradual softening regime that ended in a stress plateau that continued up to the specimen failure. The fatigue life decreased as the temperature increased. The temperature effect on life was more pronounced at low strain amplitudes. The metallography of the failed samples revealed that the fatigue failure at high amplitudes of testing was marked by extensive crack branching and the formation of secondary cracks. Oxidation was found to exert major influence on LCF life reduction at 873K.

Plastic-strain cyclic response of SiC particulate reinforced aluminum composites

The cyclic stress response characteristics of several SiC particulate reinforced aluminum composites and their unreinforced counterpart at room temperature were investigated. The as-extruded specimens were cyclically deformed with fully-reversed loading under a range of constant plastic-strain amplitudes. The test results showed that the cyclic response characteristics of the reinforced and unreinforced materials were different. During most of the fatigue life, the unreinforced aluminum mainly exhibited cyclic hardening, while the composites showed gradual softening. The dislocation substructure developed during cyclic deformation was analyzed using transmission electron microscopy. The discrepency between the dislocation substructure obtained from processing compared to its development during cyclic strain loading is thought to give rise to the observed cyclic stress response behavior.

Substructural recovery in a cold worked Ti-modified austenitic stainless steel during high temperature low cycle fatigue

Total axial strain controlled fatigue tests have been conducted in air at 823 and 923 K to ascertain the influence of cold work on LCF behaviour of a 15Cr–15Ni, Ti modified austenitic stainless steel, designated as Alloy D9. The LCF behaviour of the 20% cold worked alloy was compared with that of solution annealed alloy. A symmetrical triangular waveform at a constant strain rate of 3×10 −3 s −1 was employed for all the tests performed over the strain amplitude in the range of ±0.25 to ±1.00%. The cyclic stress response varied as a complex function of microstructure, temperature and strain amplitude. The cyclic stress response of solution-annealed alloy was generally characterized by initial hardening to the maximum stress followed by a regime of nearly stable peak stresses. The degree of initial hardening was higher at 823 K due to dynamic strain ageing effects. The cold worked alloy displayed a gradual softening prior to the attainment of saturation stress response stage. The plastic strain fatigue resistance of the cold worked alloy was inferior compared to that in solution-annealed condition at both 823 and 923 K. At low strain amplitudes, the cold worked alloy exhibited better total strain fatigue resistance at 923 K. The observed variations in fatigue life and cyclic stress response behaviour have been explained on the basis of crack initiation, development of substructure, precipitation behaviour and evolving changes in plastic strain during cycling.

Influence of temperature on cyclic stress response, strain resistance, and fracture behavior of aluminum alloy 2524

In this paper, the cyclic stress response, strain resistance, and cyclic fracture behavior of aluminum alloy 2524 is examined. Test specimens of the alloy was cycled at both the ambient and elevated temperatures using, tension-compression loading (load-ratio of −1.0), under total strain control, over a range of plastic strains giving less than 10 4 cycles to failure. The alloy displayed combinations of hardening and softening in both the longitudinal and transverse directions of the wrought plate. The alloy followed the Coffm–Manson relation, and exhibited a single slope for the variation of cyclic plastic strain amplitude with reversals to failure. Fracture of the alloy samples was predominantly transgranular for both orientations, with microscopic crack propagation along the grain boundaries. The stress response characteristics, and fracture behavior of the alloy are discussed in terms of competing and synergistic influences of cyclic plastic strain amplitude, response stress, intrinsic microstructural effects, and dislocation-microstructure interactions during cyclic straining.

Cyclic stress response and fatigue behavior of Cu added ferritic steels

Steels in which Cu content was altered from 0 to 1.5 mass% were subjected to various heat treatments to change the state of Cu. Concerning these respective steels, fatigue ratio by a stress controlled fatigue test and fatigue resistance by a strain controlled fatigue test thereof were compared. Furthermore dislocation substructure and surface defect during and after cyclic straining were investigated to clarify the effect of Cu on fatigue properties. The fatigue ratios at 2.0 × 106 loading cycles of the Cu added steels after aged at 450 and 750 degrees C are 0.7, remarkably high as compared with those of the Cu added steels after aged at 550 and 650 degrees C, the Cu free steels and any other conventional steels whose fatigue ratio are approximately between 0.5 and 0.6. The fatigue resistance of the as-rolled Cu added steel maintains steady cyclic hardening until fracture. To the contrary the Cu added steel after heat treatment at 550 degrees C shows cyclic hardening to the peak stress and then shows a cyclic softening until fracture. The surface roughness of the Cu added steels after cyclic straining are relatively shallow compared with those of the Cu free steel. The internal substructure of the Cu free steel shows typical cell structure but those of the Cu added steels exhibit vein structure.