Characteristics Of Crack Resistance Research Articles

Современные задачи механики разрушения и механики катастроф

Results of the activities of the Scientific and Methodological Commission for Standardization in the field of Fracture Mechanics of the Scientific and Technical Council of the State Standard of the USSR in connection with the 40th anniversary of its creation are presented. An emphasis is made on the results of the basic experiment in fracture mechanics in order to verify the main methodological guidelines of tests for crack resistance. A number of problematic issues and limitations arising upon testing and interpretation of the results, especially when using plastic steels and inherent strive to extend ideas and requirements of linear fracture mechanics to elastoplastic strain and fracture. The list of methodological recommendations for determining the characteristics of crack resistance for specific classes of materials and test conditions with reference to specific objects and structures previously developed by the commission and published in the late 1990s is presented. The substantial part of the methodological recommendations regulating the general approaches to carrying out calculations for crack resistance with a description of the flowchart calculations based on the criteria of fracture mechanics is given in more details. Areas of application of force, energy and deformation criteria of fracture are determined, as well as existing assurance coefficients and their allowed values are specified. The main trends and directions of the development of computational and experimental methods of fracture mechanics are considered in conclusion along with the primary goals of unification of test and computation methods used for determination of the crack resistance.

ТРЕЩИНОСТОЙКОСТЬ БАББИТА Б83

Babbit 83 crack resistance test in accordance with SSR 25-506-85 was carried out. By finite element method there were defined values of stress intensity factors in flat samples with a grown crack. The fracture viscosity characteristics of babbit are obtained. On the basis of a macro-fractographic analysis of wear fractures of a babbit sample and a finite element procedure for the definition of values of stress intensity factors the cha-racteristics of cyclic crack resistance are obtained. It is shown that a final fracture is realized at 3 МПа , and a transition from an elastic stage to the stage elastoplastic development of a crack is realized at 2,0…2,8 МПа .

Mode I and Mode II Cyclic Crack Resistance of Wheel Steel

The characteristics of the mode I and mode II cyclic crack resistance of model wheel steel are compared. The effect of heat treatment of test steel on its microstructure parameters, as well as strength and cyclic crack resistance characteristics, is studied.

Investigation of the Kinetics of Fatigue Macrocracks Under Transverse Shear

We study the kinetics of shear macrocracks under the conditions of fatigue fracture by transverse shear of thermally hardened 65G steel with a troostite-sorbite structure for low-, middle-, and high-amplitude cyclic loads. We plot the kinetic diagrams of fatigue fracture with regard for the friction of the faces of a shear crack within the range of its growth rates covering up to six orders of magnitude. On the basis of the constructed dependence, we determine the principal and additional characteristics of cyclic crack resistance. We also study the contact interaction of the faces of fatigue cracks and the fractographic features of fracture under the conditions of low- and high-amplitude deformation by cyclic transverse shear.

Influence of the Space Orientation of Joints in the Process of Welding on the Strength and Cyclic Crack Resistance of Welded Joints

We study the regularities of influence of the space orientation of a joint (at angles of 0, 30°, 45°, and 90° to the horizontal plane) for different rates of consumable-electrode pulse-arc welding (23, 40, and 57 m/h) of the sheets of AMg5M structural aluminum alloy 4 mm in thickness with the use of a ZvAMg6 filler wire on the physicomechanical properties of welded joints. It is shown that, by varying the heat input into the welded metal and the rate of crystallization of the metal in the bath, we can perform welding without using backing (forming) elements. The optimal characteristics of cyclic crack resistance of the weld metal of these welded joints are obtained in the case of orientation of joints at an angle of 30° to the horizontal plane. The preliminary monitoring of the properties of these welded joints can be performed by the nondestructive eddy-current testing method according to the specific electric conductivity of the metal.

Anisotropy of the Cyclic Crack Resistance of Aluminum Alloys After Long-Term Operation

We study the characteristics of cyclic crack resistance of specimens of D16ATNV (2024-T3-type) and V95T1 (7075-T6-type) aluminum alloys cut out from different zones of the wing of an AN-12 aircraft after 40 yr of operation along (LT-specimens) and across (TL-specimens) the direction of forge-rolling of skin sheets. It is shown that, as compared with the as-delivered state of these alloys, the D16ATNV and V95T1 aluminum alloys after long-term operation are characterized by the “reverse anisotropy” when the growth rate of fatigue macrocracks in the LT-specimens is higher than in the TL-specimens. Depending on the Al–Cu–Mg alloying system (D16-type alloy) or the Al–Zn–Mg–Cu system (V95-type alloy), this phenomenon can manifest itself in different ways in the tests carried out in air at room and low (– 60°C) temperatures and in corrosive media.

The influence of properties of metal and temperature on cyclical crack resistance of power-plant steels

The cyclical crack resistance of power-plant steels is studied. The influence of metal condition (properties) within a specific steel grade on the characteristics of cyclical crack resistance is analyzed. It is shown that, at a room temperature, i.e., in the range of viscous-brittle transition, the cyclical crack resistance of steel decreases with the increase in its tendency to the brittle state. With increasing temperature from room to 300–320°C, the cyclical crack resistance steel decreases, and for state-specific conditions, the degree of fatigue crack growth correlates with the level of yield strength decrease at the same temperature. Taking this into account, the approach to approximation of the kinetic cyclical crack resistance diagram is experimentally proved by a generalized dependence invariant to temperatures in the range 20–300 (320)°C.

The influence of aqueous environment of coolant of power plants on cyclical crack resistance of steels

The results of investigations of cyclic corrosion crack resistance of carbon steel of grade 20 and low-alloyed pipe steels of grade 15GS and 12Kh1MF are presented. The variants of water standard conditions of power plants are used as test environments. A significant activating impact of the aquatic environment on the kinetics of growth of fatigue cracks of the steels under study is shown. The most significant corrosive effect is observed when tested in an aqueous environment with addition of organic acid. In the low-frequency range of cyclical loading (0.04–0.0008 Hz), the frequency does not influence the characteristics of the cyclic corrosion crack resistance of steels. To eliminate the influence of stress cycle asymmetry on the diagram of corrosion-fatigue crack resistance of steels, it was proposed to use as a parameter of crack growth rate (CGR) the effective range of stress intensity factor (SIF), functionally associated with the factor of stress cycle asymmetry. When the temperature of the medium is increased from 80 to 150°C and to 280°C, the form of kinetic diagram of cyclic corrosion crack resistance is changed, resulting in a decrease in crack growth rate at the middle and upper sections of the diagram.

Determination of the Crack Resistance Characteristics of Graphitized Carbon Materials by the Dynamic Indentation Method

We show a correlation between the loading characteristic of crack resistance (critical stress intensity factor) and the mechanical characteristics during dynamic indentation. We propose a procedure for monitoring a material in the stage preceding its fracture. We have obtained experimental results for isotropic pyrolytic graphite that support the feasibility of the procedure and the possibility of using it for nondestructive testing of graphitized carbon materials.

Full-scale pressure vessel tests at low temperatures and external electric potential

The internal pressure test method and test results are presented for pressure vessels at a low-temperature and applied external electric potential conditions. The rupture mechanisms, plasticity and crack resistance characteristics, and times until rupture (rupture lifetimes) are compared between the tested pressure vessels and vessels exposed to a constant external electric potential. The positive effect of the external electric potential on the process of rupture of pressure vessels is noted.

ИССЛЕДОВАНИЕ ХАРАКТЕРИСТИК ЦИКЛИЧЕСКОЙ ТРЕЩИНОСТОЙКОСТИ ГРАНУЛЬНОГО СПЛАВА НА НИКЕЛЕВОЙ ОСНОВЕ С РАЗНОЙ ФРАКЦИЕЙ ГРАНУЛ

ИССЛЕДОВАНИЕ ХАРАКТЕРИСТИК ЦИКЛИЧЕСКОЙ ТРЕЩИНОСТОЙКОСТИ ГРАНУЛЬНОГО СПЛАВА НА НИКЕЛЕВОЙ ОСНОВЕ С РАЗНОЙ ФРАКЦИЕЙ ГРАНУЛ

Determination of the Characteristics of Cyclic Crack Resistance of Steels Under Transverse Shear (A Survey)

We present a survey of works devoted to the investigation of the fatigue fracture of steels under the conditions of transverse shear. Numerous methods aimed at the determination of the characteristics of cyclic crack resistance of structural steels of different strength classes are analyzed. The analysis of the results of investigations enables us to make a conclusion about the necessity of improvement of the available methods and development of new methods for the construction of the kinetic diagrams of fatigue fracture with regard for the influence of friction of the lips of fatigue cracks on the stress intensity factor K II and the elimination of stresses in the vicinity of the crack tip.

Peculiarities of corrosion degradation of steel of oil pipelines

Both domestic and foreign scholars dealt with studying various aspects of corrosion degradation of steels of oil pipelines. At present, there are numerical-analytical methods for calculating stress intensity factors for cracks of various shapes in cylindrical bodies under loads, simulating the operational loads on the oil pipeline, as well as methods for assessing the operational degradation of materials of oil pipelines. However, it is necessary to take into account the fact that degradation of the material under the long-term action of the operational factors is a multi-stage process, and the effect of each stage ultimately determines the durability of the tube element in predetermined operating conditions.Therefore, the subcritical growth of corrosion or crack-like defects, caused by the combined action of operating loads and media is crucial. In current approaches, these processes have not yet been sufficiently investigated and are not taken into account when predicting the performance of oil pipelines, in particular degradation of physical and mechanical properties of the metal used. Engineering evaluation of the rate of corrosion failure of oil pipelines, taking into account both mechanical and physicochemical parameters of the interaction of the deformed metal with the working medium was carried out in the paper. The characteristics of the cyclic corrosion crack resistance of the metal of the pipe of oil pipelines taking into account the effect of operational factors. New data about the features of corrosion-fatigue failure of pipes depending on the original sizes and shape of the defects were obtained. Diagrams of cyclic crack resistance of unexploited and exploited pipe steels 10Г2БТЮ3 and steel 20 were built. It was found that the water corrosive media (soil and distilled water) significantly affect the propagation process of fatigue crack in the studied steels.

Cold In-Place Recycling as a Sustainable Pavement Practice

Pavement rehabilitation and reconstruction methods with CIR (cold in-place recycling) are alternatives that can effectively reduce the high stresses and waste produced by conventional pavement strategies. An attempt was made to predict the performance, particularly low-temperature cracking resistance characteristics of CIR mixtures. These were prepared with the mix design procedure developed at the URI (University of Rhode Island) for the FHW A (Federal Highway Administration) to reduce wide variations in the application ofCIR mixtures production. This standard was applied to RAP (reclaimed asphalt pavement) to produce CIR mixtures with CSS-lh asphalt emulsion as the additive. By adjusting the number of gyrations of the SGC (Superpave gyratory compactor) for compaction, the field density of 130 pcf was represented accurately. To secure a base line, HMA (hot mix asphalt) samples were produced according to the Superpave volumetric mix design procedure. The specimens were tested using the IDT (indirect tensile) tester according to the procedure of AASHTO T 322 procedure at temperatures of -20, -10 and 0 °C ( -4, 14, and 32 Gp, respectively). The obtained results for the creep compliance and tensile strength were used as input data for the MEPDG (mechanistic empirical pavement design gnide ). The analysis results indicated that no thermal or low-temperature cracking is expected over the entire analysis period of 20 years for both HMA and CIR mixtures. Thus, it appears that CIR is a sustainable rehabilitation technique which is also suitable for colder climates, and it is reconunended to conduct further investigation ofload-related distresses such as rotting and fatigue cracking.

Methods for the Construction of the Kinetic Diagrams of Fatigue Fracture for Steels Under the Conditions of Trаnsverse Shear with Regard for the Friction of Crack Lips

We propose the design of a specimen for the investigation of the fatigue fracture of steels under trans- verse shear. A formula for the determination of the stress intensity factor with regard for the friction of crack lips is obtained with the use of the finite-element method. The methods aimed at the construction of the kinetic diagrams of fatigue fracture under the conditions of transverse shear are developed and tested on specimens of 65G structural steel. We plot the kinetic diagram of fatigue fracture and approx- imate its middle segment by a linear dependence in the established parameters. The life of structural elements with sharp concentrators operating the under conditions of shear stresses should be evaluated on the basis of the approaches of fatigue fracture mechanics under the conditions of trans- verse shear. This is why it is necessary to develop methodical recommendations for the reliable determination of the characteristics of cyclic crack resistance (CCCR) of the materials in transverse shear. In the case of mode I fatigue fracture of metallic materials, the methods aimed at the determination of the CCCR were standardized in (1). Some experimental investigations of the mode II fatigue fracture of steels based on the models neglecting the stage of stable growth of fatigue cracks or the friction of their lips are also known (2-5). This negatively affects the analysis of the stress-strain state (SSS) near the crack tip, the determi- nation of the CCCR of materials, and the evaluation of the service life of structural elements as a whole, which should be taken into account in the development of new methods for the construction of the kinetic diagram of fatigue fracture (KDFF) in transverse shear. The aim of the present work is to develop new methods for the construction of the KDFF and evaluation of the CCCR of steels in transverse shear with regard for the friction of crack lips.

Экспериментальное определение характеристик трещиностойкости фибробетона

Экспериментальное определение характеристик трещиностойкости фибробетона

Fracture mechanics of multimodulus dilatant media

Cracks arising in dilatant and multimodulus materials (different elasticity moduli for different types of the stress state) are under study. The stress and strain distributions in dilatant multimodulus bodies with cracks, which allow estimating the impact of damage on crack resistance characteristics, are investigated.

Effect of Temperature on Environmental Stress Cracking Resistance and Crystal Structure of Polyethylene

Studies were conducted on the crystalline properties of different polyethylene resins to identify their influence on phase interconnectivity between amorphous and crystalline regions. This work offers a thorough investigation on the potential correlation between environmental stress cracking resistance (ESCR) and crystalline structure characteristics, namely, crystallinity, mean lamella thickness and its distribution, and lamella surface area (LSA). The initial objective of this work was to investigate an existing ambiguity in the literature with respect to the effect of the crystalline phase on ESCR. In addition, research was conducted to evaluate the degree of variability in the lamella surface area, as a measure of phase interconnectivity and ESCR, with processing temperature and post-process annealing. Annealing at various conditions, along with cooling at different rates, were employed to investigate the effect of temperature on LSA. It was observed that a clear correlation exists between crystalline phase properties and ESCR, given that the comparison is made between polymers with similar molecular weights. Annealing temperature and time were found to cause a general reduction in LSA, however, to varying degrees, according to the type of PE molecular structure (significant interactions exist between annealing conditions and polymer type). LSA showed a significant dependence on cooling rate, however, no interaction was found between cooling rate and type of PE molecular structure. Additionally, lamella surface areas obtained from quenching and air cooling were found to be almost the same.

Fatigue strength of high-alloy corrosion-resistant TRIP steels (review)

The changes in the structural state of high-alloy TRIP steels during cyclic deformation in low- and high-cycle fatigue regions and the cyclic cracking resistance characteristics are analyzed. The strain-induced martensite that forms during cyclic deformation is shown to substantially affect the cyclic strength characteristics of the TRIP steels.

Influence of Long-Term Operation on the Structure and Physicomechanical Properties of D16- and V95-Type Aluminum Alloys

We establish the fact of degradation of the properties in D16- and V95-type alloys from the wing skin of an AN-12 airplane after long-term operation for 40 yr, which mainly manifests itself in the decrease in their plasticity (relative elongation δ) and the characteristics of cyclic crack-resistance (fatigue threshold ΔK th and cyclic fracture toughness ΔK fc). It is shown that the degradation of the mechanical characteristics of these alloys is connected with the changes in their fine structure and the mechanisms of microfracture depending on the level of loading of different zones of the wing. It is shown that the process of degradation can be monitored by analyzing the changes in the electric conductivity of the degraded alloys.