scholarly journals Analysis of the initial stage of fatigue wear in heterostructure materials under contact cyclic loading

2020 ◽  
Vol 19 (4) ◽  
pp. 328-334
Author(s):  
O. V. Kudryakov ◽  
V. N. Varavka ◽  
I. Yu. Zabiyaka ◽  
E. A. Yadrets ◽  
O. V. Shvedchikova
Keyword(s):  
Cyclic Loading ◽  
Physical Model ◽  
Erosive Wear ◽  
Material Structure ◽  
Fatigue Wear ◽  
Structural Morphology ◽  
Nucleation Stage ◽  
Defect Nucleation ◽  
The Moment ◽  
Instrumental Methods

Introduction. The process of formation of fatigue defects in metal alloys with different structural morphology is considered. The work objective is to develop a computational tool for determining the moment of the defect nucleation under cyclic loading.Materials and Methods. A physical model is built, calculation expressions are presented. The physical model is based on the theory of dislocations. It is shown that a structure factor is particularly important in the process of fracture nucleus origination under dynamic cyclic loading. Depending on the structure and properties of the material, as well as on the nature of the loads, the critical fatigue defect develops in the form of cracks, pores or micro-crater wear.Research Results. A numerical experiment was performed to determine the moment of nucleation of the critical-size defect in iron-base alloys under the drop hypervelocity impacts. Comparative data of calculations and bench tests for droplet impingement erosion of steels and alloys with the structure of ferrite, austenite, sorbitol and martensite are presented. The efficiency of the nucleation stage during the incubation period of erosive wear of the materials studied was evaluated.Discussion and Conclusions. There are no strict instrumental methods for determining the duration of the nucleation stage; therefore, it is recommended to use the proposed analytical model. In addition, the work performed gave a significant application result, i.e. it showed that the focused design of the material structure can significantly increase the wear resistance.  

Patterns of Fracture Initiation in Metallic Materials with a Heterogeneous Structure under Dynamic Cyclic Loading

2020 ◽  
Vol 989 ◽  
pp. 127-132
Author(s):  
Oleg V. Kudryakov ◽  
Valery N. Varavka ◽  
Igor S. Morozkin
Keyword(s):  
Cyclic Loading ◽  
Physical Model ◽  
High Speed ◽  
Erosive Wear ◽  
Fracture Initiation ◽  
Heterogeneous Structure ◽  
Structural Morphology ◽  
Nucleation Stage ◽  
The Moment ◽  
Instrumental Methods

The process of nucleation of fatigue defects in metal alloys with different structural morphology is considered. A physical model was built, calculation expressions were presented, a numerical experiment was performed to determine the moment of nucleation of the critical-size defect in Fe-based alloys during high-speed droplet impacts. The physical model is based on the theory of dislocations. It is shown that the determining factor in the process of wear nucleation under dynamic cyclic loading has a structural factor. Depending on the structure and properties of the material, as well as on the nature of the loads, the critical fatigue defect develops in the form of cracks, pores or microcraters. Comparative data of calculations and bench tests for droplet impingement erosion were presented. The contribution of the nucleation stage during the incubation period of erosive wear of the materials studied was evaluated. Due to the fact that rigorous instrumental methods for determining the duration of the nucleation stage are absent, the usage of the proposed analytical model is recommended for this purpose.

scholarly journals Analysis of Damage Evolution in Concrete under Fatigue Loading by Acoustic Emission and Ultrasonic Testing

Materials ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 341
Author(s):  
Marc Thiele ◽  
Stephan Pirskawetz
Keyword(s):  
Acoustic Emission ◽  
Elastic Modulus ◽  
Cyclic Loading ◽  
Fatigue Damage ◽  
Fatigue Loading ◽  
Measurement Methods ◽  
Material Structure ◽  
Fatigue Process ◽  
Acoustic Methods ◽  
Normal Strength

The fatigue process of concrete under compressive cyclic loading is still not completely explored. The corresponding damage processes within the material structure are especially not entirely investigated. The application of acoustic measurement methods enables a better insight into the processes of the fatigue in concrete. Normal strength concrete was investigated under compressive cyclic loading with regard to the fatigue process by using acoustic methods in combination with other nondestructive measurement methods. Acoustic emission and ultrasonic signal measurements were applied together with measurements of strains, elastic modulus, and static strength. It was possible to determine the anisotropic character of the fatigue damage caused by uniaxial loading based on the ultrasonic measurements. Furthermore, it was observed that the fatigue damage seems to consist not exclusively of load parallel oriented crack structures. Rather, crack structures perpendicular to the load as well as local compacting are likely components of the fatigue damage. Additionally, the ultrasonic velocity appears to be a good indicator for fatigue damage beside the elastic modulus. It can be concluded that acoustic methods allow an observation of the fatigue process in concrete and a better understanding, especially in combination with further measurement methods.

Effect of Erosive Particle Velocity on the Intensity of Polymeric Coating Wear

2010 ◽  
Vol 165 ◽  
pp. 91-96 ◽  
Author(s):  
Danuta Kotnarowska
Keyword(s):  
Experimental Investigation ◽  
Grain Size ◽  
Particle Velocity ◽  
Erosive Wear ◽  
Wear Intensity ◽  
Polymeric Coating ◽  
Degree Polynomial ◽  
Acrylic Coating ◽  
The Moment ◽  
Free Falling

The paper deals with experimental investigation of erosive wear of acrylic coating. The research was carried out on the erosive wear under the influence of alundum particles (grain size of 0.6 – 0.7 mm) striking the coatings at the angle of 45 degrees. It was established that intensity of the erosive wear (under the influence of free falling alundum particles) essentially depends on velocity of erosive particle at the moment of its impact against coating surface. For example, for the lowest velocity value (3.6 m/s) at the moment of impact, erosive wear intensity was equal to 0.4 mm/kg, while for the largest velocity value (5.3 m/s), the intensity doubled in magnitude. The characteristic of erosive wear intensity, depending on erosive particle velocity, was generated by using second-degree polynomial.

Study of Constitutive Relationship Model of Material Structure Based on Full State Function

2012 ◽  
Vol 174-177 ◽  
pp. 1566-1573
Author(s):  
Zhen Hai Wei ◽  
Meng Shu Wang ◽  
Ding Li Zhang
Keyword(s):  
Structural Properties ◽  
Plastic Material ◽  
Structural Evolution ◽  
Theoretical Method ◽  
Constitutive Relationship ◽  
Material Structure ◽  
State Function ◽  
Structural Morphology ◽  
Structural Problems ◽  
Full State

The structural problem is the key and difficult point for the study of material composed of granules. In this paper, theory of full state function for material structure is put forward by examining the structural morphology of the material. The full state function of material structure reflects the structural properties of material. Thus it can also reflect the variations in of mechanical and geometric properties of material under external force, i.e. the constitutive relationship of material. The constitutive relationship established based on full state function is abbreviated as "full constitutive relationship”, which considers the structural properties of material. The constitutive relationship not only can derive constitutive relationship which considers material structure, but also the constitutive relationship with the identical form as that in classical theory when material degenerates into typical ideal elastic-plastic material. The theoretical method proposed in this paper transforms dynamic analysis of structural evolution into state analysis. By associating granular scale with macroscopic scale, a foundation is laid for solving of the structural problems of material macroscopically.

scholarly journals Properties of coatings created by HVOF technology using micro-and nano-sized powder

2019 ◽  
Vol 63 (2) ◽  
pp. 86-93 ◽  
Author(s):  
A. Guzanová ◽  
J. Brezinová ◽  
D. Draganovská ◽  
P.O. Maruschak
Keyword(s):  
Corrosion Resistance ◽  
Cyclic Loading ◽  
Linear Polarization ◽  
Elevated Temperatures ◽  
Erosive Wear ◽  
Wear Test ◽  
Thermal Cycles ◽  
Properties Of Coatings ◽  
Grain Sizes ◽  
Sprayed Coatings

Abstract The paper focuses on assessment the resistance of hot-sprayed coatings applied by HVOF technology (WC–Co–Cr created using powder of two different grain sizes) against erosive wear by dry-pot wear test in a pin mill at two sample angles. As these coatings are designated for the environment with varying elevated temperatures and often are in contact with the abrasive, the coatings have been subjected to thermal cyclic loading and their erosive resistance has been determined in as-sprayed condition and after the 5th and 10th thermal cycles. The corrosion resistance of coatings was evaluated by linear polarization (Tafel analysis).

scholarly journals KUHN-TUCKER CONDITIONS IN SHAKEDOWN PROBLEMS

1996 ◽  
Vol 2 (5) ◽  
pp. 14-28
Author(s):  
Juozas Atkočiūnas
Keyword(s):  
Cyclic Loading ◽  
Mathematical Programming ◽  
Safety Factor ◽  
Strain Field ◽  
Analysis Problem ◽  
Cyclic Plastic ◽  
Perfectly Plastic ◽  
History Of ◽  
Elastic Perfectly Plastic ◽  
The Moment

An elastic perfectly plastic structure at shakedown to given cyclić loading is under consideration. The stress-strain field of dissipative system in general is related to the history of loading. And only in a particular case, i.e. at the moment prior to the failure of an elastic perfectly plastic structure the distribution of the actual residual forces is unique for each prescribed history of loading (the safety factor of shakedown approaches unity). Nevertheless, there exist some domains where the plastic strains are equal to zero. The residual forces in the statically indeterminate parts of the structure may be non-unique: the stress field is only determined by the equilibrium equations. The extremum energy principle of minimum complementary energy allows to derive the actual residual forces out of all statically admissible residual forces at the moment prior to cyclic plastic failure. Then the stress-strain field analysis problem at the moment prior to the cyclic plastic failure is formulated as a problem of non-linear mathematical programming. Formulating the dual pair of non-linear programming problem (statical and kinematic formulation of analysis problem) the differential constraints are neglected or replaced by algebraic conditions. When the safety factor is approching a unity, the degeneracy of the statical formulation of the analysis problem often can occur. In this case a mathematical model is proposed for obtaining an upper bounds for the displacement at shakedown. It is pointed out that the known Kuhn-Tucker conditions of mathematical programming theory (i.e. compatibility equations of residual strains) in concert with restriction, limiting the maximum value of total energy dissipation, make up the adaptation conditions of the structure to given cyclic loading. Kuhn-Tucker conditions used in above—mentioned problem allow to correctly interprete the physical aspect of the degeneracy problem at shakedown. When the safety factor is larger than unity an artificial degeneracy situation for the statical formulation of analysis problem can be created. Then the mathematical models presented can be applied to the analysis of unloading elastoplastic structures. With this aim in view a fictitious equiplastic structure the behaviour of which is holonomic is derived. The displacements of the fictitious structure enclose the displacements of the actual structure subject to cyclic loading.

scholarly journals Restoring Force Model of an Energy-Dissipation Joint in Hybrid Frames: Simplified Skeleton Curve and Hysteretic Rules

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Yanhua Wang ◽  
Yan Feng ◽  
Dongsheng Huang ◽  
Zirui Huang ◽  
Zhongfan Chen
Keyword(s):  
Energy Dissipation ◽  
Cyclic Loading ◽  
Critical Points ◽  
Damping Ratio ◽  
Force Model ◽  
Restoring Force ◽  
Theoretical Derivation ◽  
Skeleton Curve ◽  
Restoring Force Model ◽  
The Moment

In this paper, a restoring force model, composed of a trilinear skeleton curve and hysteretic rules, is proposed based on nine pseudostatic tests of the energy-dissipation joint under horizontal low cyclic loading. The critical points of the simplified skeleton curve are obtained via theoretical derivation and FE simulation. The hysteretic rules for the joints are simplified as a concave hexagon, where the parameters of the critical points are optimized by the genetic algorithm (GA). Using the established trilinear skeleton curve, three different working stages, i.e., elastic, hardening, and softening, were divided by the critical points and the moment stiffness of three stages can be calculated. The proposed hysteretic rules of each stage can reveal and explain the “pinching” in the cyclic loading, which make it easier to understand the mechanism of the energy-dissipation joint. The comparison between the restoring force model and the tests shows that the simplified skeleton curves, the established hysteretic rules, and the ductility and the damping ratio are consistent with the experimental results. Finally, the effectiveness of the established restoring force model is verified.

Study of Alternative Materials to Minimize Erosion in Heat Exchanger Tubes Used in Thermoelectric Generators

2008 ◽  
Vol 591-593 ◽  
pp. 49-54
Author(s):  
A.B.C. Arnt ◽  
Marcos Marques da Silva Paula ◽  
Márcio Roberto da Rocha ◽  
Elidio Angioletto ◽  
L.C. Zanini ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Erosive Wear ◽  
Cost Benefit ◽  
Heat Pipes ◽  
The Real ◽  
Combustion Gases ◽  
Maintenance Schedule ◽  
Operation Conditions ◽  
The Moment

The machinery used in coal thermoelectrical plants usually is submitted to erosive wear. The erosive wear occurs mainly in the metallic pipe set of heat exchangers due the flow of hot gases carrying erosive particles. Jorge Lacerda’s thermoelectrical complex at Capivari de Baixo city holds seven power units, where two units use approximately 20 000 ASTM A178 heat pipes. The set is submitted to a semester maintenance schedule (preventive and corrective) where the damaged pipes are changed. So, in this work a set of erosive wear accelerated tests according ASTM G76 were performed in order to develop and specify materials and methods to diminish the erosive action caused by the combustion gases over the heat pipes. Specimens were coated with WC12Co and Cr3C2-25NiCr alloys using the HVOF technique and the coated specimens were tested at 450°C, the heat pipes working temperature. Silica was used as abrasive material at 30° and 45° impact angles, simulating a harder erosive condition than the real condition. The best performance coating at laboratory scale was later used in field condition. The results showed the coated specimen performance is better than the ASTM A178 alloy. The erosion resistance of the Cr3C2-25NiCr and WC12Co coatings is eight times higher than the uncoated alloy, and the coatings also presented a better corrosion resistance. This feature is important, because despite the erosive action the circulating gases also present a large amount of sulfur in their composition. Sulfur at lower temperatures forms H2SO4, causing intense corrosion of the pipes located at the heat exchangers colder parts. Based on the results and considering the coating costs the Cr3C2-25NiCr alloy was selected to coat a set of pipes mounted at the region of the heat exchanger with the most intense erosive wear. At the moment these coated tubes are in field operation and under observation regarding their performance in comparison with the uncoated pipes located at the same heat exchanger. The real operation conditions of the coated pipes will be estimated from the field life cycle analysis, and after all the cost-benefit of the studied coating.

Structure Peculiarities of Nanocomposite Powder Fe40Al/Al2O3 Produced by MASHS

2007 ◽  
Vol 534-536 ◽  
pp. 1421-1424 ◽  
Author(s):  
Tatsiana Talaka ◽  
Tatiana F. Grigorieva ◽  
Piotr Vitiaz ◽  
Nikolay Lyakhov ◽  
Andrey Letsko ◽  
...  
Keyword(s):  
Mechanical Activation ◽  
Composite Powder ◽  
Interfacial Strength ◽  
Second Step ◽  
Material Structure ◽  
Structure Investigation ◽  
Nanocomposite Powder ◽  
Structural Morphology ◽  
Production Route ◽  
Two Stages

Structure investigation results for MASHS powder Fe40Al/Al2O3 are presented. The powder structure formation proceeds via two stages. On the first step (mechanical activation) aluminothermal reaction takes plays in the system Fe+Al+Fe2O3, leading to formation of nanocomposite precursor Fe-Al-Al2O3. On the second step (SHS), iron and aluminum reacts, forming intermetallic FeAl. As-synthesized composite powder completely inherits the precursor structural morphology in spite of the phase transformations taking place during the production process. Such a production route provides the formation of intergrowth nanocomposite material structure with improved interfacial strength.

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