scholarly journals FATIGUE FAILURE AS A COMPLEX OF RELAXATION PROCESSES OCCURRED AT THE VERTICES OF THE STRESS RISERS

InterConf ◽  
2021 ◽  
pp. 341-348
Author(s):  
P. Volosevish ◽  
B. Mordyuk
Keyword(s):  
Fatigue Life ◽  
Fatigue Failure ◽  
Grain Boundary Sliding ◽  
Polycrystalline Materials ◽  
Second Phase ◽  
Relaxation Processes ◽  
Stress Risers ◽  
Eye Fatigue ◽  
Surface Modified ◽  
Stress Dependent

This paper considers the stress-dependent fatigue life of polycrystalline materials and their fatigue failure as a result of the relaxation processes that occurred on the stress risers of various scales: macroscopic stress risers of technological nature (pores, cracks, surface roughness, etc.), and microscopic stress risers at the grain/subgrain boundaries and/or second phase particles. Participation of the relaxation mechanisms plastic (vacancies and dislocation activities, grain boundary sliding) and brittle (cracks) nature in the process of the ‘fish eye’ fatigue crack formation is also addressed. The model described the parabolic dependencies of the densities of elementary carriers of plastic and brittle relaxations on the load change rate (i.e., on the growth rate of the stresses concentrated at the vertices of the stress risers) correlates well to the fatigue life data observed for the surface-modified metallic materials.

Analytical Electron Microscopy of Surface-Modified Ceramics

1985 ◽  
Vol 43 ◽  
pp. 276-279
Author(s):  
P. S. Sklad
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Theoretical Models ◽  
Ceramic Materials ◽  
Solute Concentration ◽  
Second Phase ◽  
Analytical Electron ◽  
Implantation Techniques ◽  
Lattice Damage ◽  
Surface Modified

Over the past several years, it has become increasingly evident that materials for proposed advanced energy systems will be required to operate at high temperatures and in aggressive environments. These constraints make structural ceramics attractive materials for these systems. However it is well known that the condition of the specimen surface of ceramic materials is often critical in controlling properties such as fracture toughness, oxidation resistance, and wear resistance. Ion implantation techniques offer the potential of overcoming some of the surface related limitations.While the effects of implantation on surface sensitive properties may be measured indpendently, it is important to understand the microstructural evolution leading to these changes. Analytical electron microscopy provides a useful tool for characterizing the microstructures produced in terms of solute concentration profiles, second phase formation, lattice damage, crystallinity of the implanted layer, and annealing behavior. Such analyses allow correlations to be made with theoretical models, property measurements, and results of complimentary techniques.

Calculation Error Analysis on the Strain Fatigue Life Predication Formula of Manson-Coffinn and Damage Stain Model

2011 ◽  
Vol 197-198 ◽  
pp. 1599-1603
Author(s):  
Zhen Wei Wang ◽  
Ping An Du ◽  
Ya Ting Yu
Keyword(s):  
Fatigue Life ◽  
Error Analysis ◽  
Fatigue Failure ◽  
High Speed ◽  
Production Cost ◽  
Calculation Error ◽  
Mechanical Components ◽  
Strain Model ◽  
Engine Crankshaft

Mechanical components are subjected heavy alternate load in industries, such as engine crankshaft, wheel axle, etc. The fatigue failure happens after a long work loading, which affects the production cost, safe and time. So the fatigue life predication is fundamental for the mechanical components design. Especially, it is very important for heavy, high-speed machinery. In this paper, both main fatigue life predication formulas are introduced briefly, including Manson-Coffinn formula and Damage strain model. Then, shortages of above life predication formulas are pointed out, and coefficients are explained in detail. Further calculation error analysis is conducted on the basis of experiments on 16 materials. Results show that above life predication formulas lack calculation accuracy. Finally, it is pointed out that coefficients of fatigue life predication formulas are dependent of material performance. So it is unreliable that coefficients are constants for Manson-Coffin and Damage strain model.

scholarly journals Analysis of Compressive Fatigue Failure of Recycled Aggregate Concrete

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4620
Author(s):  
Fan You ◽  
Surong Luo ◽  
Jianlan Zheng ◽  
Kaibin Lin
Keyword(s):  
Fatigue Life ◽  
Fatigue Failure ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Recycled Aggregate Concrete ◽  
Construction And Demolition Waste ◽  
Recycled Aggregate ◽  
Cycle Fatigue ◽  
Demolition Waste ◽  
Aggregate Concrete

Using recycled aggregate in concrete is effective in recycling construction and demolition waste. It is of critical significance to understand the fatigue properties of recycled aggregate concrete (RAC) to implement it safely in structures subjected to repeated or fatigue load. In this study, a series of fatigue tests was performed to investigate the compressive fatigue behavior of RAC. The performance of interfacial transition zones (ITZs) was analyzed by nanoindentation. Moreover, the influence of ITZs on the fatigue life of RAC was discussed. The results showed that the fatigue life of RAC obeyed the Weibull distribution, and the S-N-p equation could be obtained based on the fitting of Weibull parameters. In the high cycle fatigue zone (N≥104), the fatigue life of RAC was lower than that of natural aggregate concrete (NAC) under the same stress level. The fatigue deformation of RAC presented a three-stage deformation regularity, and the maximum deformation at the point of fatigue failure closely matched the monotonic stress-strain envelope. The multiple ITZs matched the weak areas of RAC, and the negative effect of ITZs on the fatigue life of RAC in the high cycle fatigue zone was found to be greater than that of NAC.

scholarly journals Bone-Inspired Microarchitectured Materials with Enhanced Fatigue Life

2018 ◽  
Author(s):  
Ashley M. Torres ◽  
Adwait A. Trikanad ◽  
Cameron A. Aubin ◽  
Floor M. Lambers ◽  
Marysol Luna ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Cyclic Loading ◽  
Energy Absorption ◽  
Fatigue Failure ◽  
Cancellous Bone ◽  
Axial Stiffness ◽  
High Porosity ◽  
Preferred Direction ◽  
Naturally Occurring ◽  
Apparent Stiffness

Microarchitectured materials achieve superior mechanical properties through geometry rather than composition 1-4. Although lightweight, high-porosity microarchitectured materials can have high stiffness and strength, stress concentrations within the microstructure can cause flaw intolerance under cyclic loading 5,6, limiting fatigue life. However, it is not known how microarchitecture contributes to fatigue life. Naturally occurring materials can display exceptional mechanical performance and are useful models for the design of microarchitectured materials 7,8. Cancellous bone is a naturally occurring microarchitectured material that often survives decades of habitual cyclic loading without failure. Here we show that resistance to fatigue failure in cancellous bone is sensitive to the proportion of material oriented transverse to applied loads – a 30% increase in density caused by thickening transversely oriented struts increases fatigue life by 10-100 times. This finding is surprising in that transversely oriented struts have negligible effects on axial stiffness, strength and energy absorption. The effects of transversely oriented material on fatigue life are also present in synthetic lattice microstructures. In both cancellous bone and synthetic microarchitectures, the fatigue life can be predicted using the applied cyclic stress after adjustment for apparent stiffness and the proportion of the microstructure oriented transverse to applied loading. In the design of microarchitectured materials, stiffness, strength and energy absorption is often enhanced by aligning the microstructure in a preferred direction. Our findings show that introduction of such anisotropy, by reducing the amount of material oriented transverse to loading, comes at the cost of reduced fatigue life. Fatigue failure of durable devices and components generates substantial economic costs associated with repair and replacement. As advancements in additive manufacturing expand the use of microarchitectured materials to reusable devices including aerospace applications, it is increasingly necessary to balance the need for fatigue life with those of strength and density.

scholarly journals Effects of Pre-Tensile Deformation on the Fatigue Fracture Behavior of Annealed 7005 Aluminum Alloy Plate

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 623
Author(s):  
Ni Tian ◽  
Zhen Feng ◽  
Xu Shi ◽  
Wenze Wang ◽  
Kun Liu ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Fatigue Fracture ◽  
Tensile Deformation ◽  
Thin Strip ◽  
Second Phase ◽  
Alloy Matrix ◽  
Alloy Plate ◽  
Dislocation Distribution ◽  
Aluminum Alloy Plate

In the present study, the fatigue life and fatigue fracture characteristics of annealed 7005 aluminum alloy plates subjected to different pre-tensile deformations were investigated. The results obtained upon increasing the pre-tensile deformation of the alloy plate to 20% revealed that the second-phase particles did not show any obvious changes, and that the thickness of the thin strip grain slightly decreased. The dislocation distribution in the alloy matrix varied significantly among the grains or within each grain as the dislocation density gradually increased with increasing pre-tensile deformation. Moreover, the fatigue performance of the annealed 7005 aluminum alloy plate was significantly improved by the pre-tensile deformation, and the alloy plate subjected to 20% pre-tensile deformation exhibited an optimal fatigue life of ~1.06 × 106 cycles, which was 5.7 times and 5.3 times that of the undeformed and 3% pre-stretched alloy plates, respectively. Two fatigue life plateaus were observed in the pre-tensile deformation ranges of 3–5% and 8–12%, which corresponded to heterogeneous dislocation distribution among various grains and within each grain, respectively. Moreover, two large leaps in the plot of the fatigue-life–pre-tensile-deformation curve were observed, corresponding to the pre-tensile deformation ranges of 5–8% and 16–20%, respectively.

Research on Micro-Mechanism of Nanocomposite Ceramic in Two-Dimensional Ultrasound Grinding

2007 ◽  
Vol 359-360 ◽  
pp. 344-348 ◽  
Author(s):  
Bo Zhao ◽  
Yan Wu ◽  
Guo Fu Gao ◽  
Feng Jiao
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Deformation Mechanism ◽  
Ground Surface ◽  
Grain Boundary Sliding ◽  
Second Phase ◽  
Two Dimensional ◽  
Composite Ceramics ◽  
Nano Composite ◽  
Boundary Sliding

Surface microstructure of nano-composite ceramics prepared by mixed coherence system and machined by two-dimensional ultrasonic precision grinding was researched using TEM, SEM, XRD detector and other equipments. Structure, formation mechanism and characteristic of metamorphic layer of ground surface of nano-composite ceramics were researched. The experiment shows micro deformation mechanism of ceramic material in two-dimensional ultrasound grinding is twin grain boundary and grain-boundary sliding for Al2O3, and it is crystal dislocation of enhanced phase, matrix grain boundary sliding, coordination deformation of intergranular second phase as well as its deformation mechanism for nano-composite ceramics. The fracture surfaces of nano-composite materials with different microscopic structure were observed using TEM and SEM. Research shows that ZrO2 plays an important influence on the generation and expansion of crack, and enhances the strength of grain boundaries. When grain boundaries is rich in the ZrO2 particles, the crack produced in grinding process will be prevented, and the surface with plastic deformation will be smooth. The results shows nanoparticles dispersed in grain boundary prevents crack propagation and makes materials fracture transgranularly which makes the processed surface fine.

Migrating Interfaces in Sapphire Bicrystals and Tricrystals

2000 ◽  
Vol 6 (S2) ◽  
pp. 386-387
Author(s):  
N. Ravishankar ◽  
M.T. Johnson ◽  
C. Barry Carter
Keyword(s):  
Mass Transport ◽  
Liquid Film ◽  
Grain Boundaries ◽  
Ostwald Ripening ◽  
Chemical Potential ◽  
Driving Forces ◽  
Boundary Migration ◽  
Liquid Phase Sintering ◽  
Polycrystalline Materials ◽  
Second Phase

The migration of grain boundaries in polycrystalline materials can occur under a variety of driving forces. Grain growth in a single-phase material and Ostwald ripening of a second phase are two common processes involving boundary migration. The mass transport in each of these cases can be related to a chemical potential difference across the grains; due to curvature in the former case and due to a difference in the chemistry in the latter case. The mass transport across grains controls the densification process during sintering. In the case of liquid-phase sintering (LPS), a liquid film may be present at the grain boundaries which results in an enhanced mass transport between grains leading to faster densification. Hence, in LPS, it is important to understand mass transport across and along a boundary containing a liquid film. The use of bicrystals and tricrystals with glass layers in the boundary can provide a controlled geometry by which to study this phenomenon.

scholarly journals Fatigue Life Characteristics of Segmental Lining Structure for the Shallow Buried Metro Tunnel under the Dynamic Load of a High-Speed Railway

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Wangping Qian ◽  
Taiyue Qi ◽  
Qing Zhao ◽  
Bingrong Pu ◽  
Jin Zhang ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Fatigue Failure ◽  
Dynamic Load ◽  
High Speed ◽  
Dynamic Loads ◽  
High Speed Railway ◽  
Segmental Lining ◽  
Lining Structure ◽  
Metro Tunnel

Shallow buried shield metro tunnels constructed underneath subgrade project of high-speed railways are becoming increasingly common in China, but the lower metro tunnel bears the fatigue effect of dynamic load induced by the upper high-speed railway, so the long-term durability of segmental lining is a nonnegligible problem. The segmental lining structure of metro tunnel is in a state of static-dynamic loads for a long time, especially when a high-speed railway passes above the metro line, and the long-term durability of segmental lining needs further research. Based on theoretical analysis, the effect of different forms of loads on the fatigue life was analyzed, the change law of the static-dynamic loads on segmental lining was summarized, and the method was put forward to evaluate the fatigue life characteristics of segmental lining. The research results reveal that the additional dynamic load is the fundamental reason for the fatigue failure of the structure, and the existence of static load can cause and accelerate the occurrence of structural fatigue failure simultaneously. The results indicate that the fatigue life decreases gradually with the increase of static-dynamic load. Based on coupling analysis of static-dynamic loads of segmental lining, the fatigue life increases first and then decreases with the increase of buried depth of metro tunnel, and it remains unchanged when the depth exceeds a certain value. According to the actual metro tunnel engineering, by using ABAQUS software, a three-dimensional numerical simulation was carried out to analyze the characteristics of the fatigue life and evolution rules of segmental lining. Based on the modified fatigue life formula and metro service life, the optimization design of the buried depth was carried out to determine the most reasonable range of the buried depth. This study provides a valuable reference for safe operation and long-term durability of metro tunnels under high-speed railways.

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