Detection and measurement of surface cracks by the ultrasonic method for evaluating fatigue failure of metals

The problem of measuring the dimensions of safe cracks by the acoustic method was considered on the basis of the concept of safe cracks. The results of investigations are presented and the obtained data on the detection and measurement of the depth of surface cracks using Rayleigh waves at artificial reflectors of the surface-notch type and at real cracks and specimens, which are subjected to cyclic loads during the “growth” of fatigue cracks, are analyzed.     

Solution of reciprocal problem of magnetic flaw detection through calculation of multipole moments of an elliptic flaw

An algorithm has been developed for calculating parameters of an effective elliptic flaw (EEF) on the base of changes in the magnetic field intensity in the air. EEF is defined as a flaw with an elliptic cross section whose magnetic moments (dipole, quadrupole, and octupole), hence the field at a large distance, are the same as those of a given flaw with an arbitrary shape. The relation between the parameters of EEF and real flaws has been established by solving Grinberg’s integral equation for internal and surface flaws of the two-dimensional configuration in a half-space filled with a linear (μ=const) ferromagnetic material. This relation was used in drawing up the solution of the reciprocal problem of magnetic flaw detection.     

A decrease in the error of the statistical method for estimating the parameters of flaws in magnetic flaw detection

A method for increasing the accuracy of evaluating the dimensions of flaws during magnetic flaw detection in steel sheets and pipes, which is based on the division of a set of flaws into subclasses using a certain generalized parameter in accordance with the criterion of minimization of an appropriate estimate, is described. The results of applicability of this method to the evaluation of the depths of flaws of the metal loss type are presented.     

The main advantage of electromagnetic-acoustic testing technique

From the analysis of previously published and new experimental data follows the conclusion that flaw detection data obtained with the help of electromagnetic-acoustic (EMA) transducers have better reproducibility than measurements by direct-contact transducers. The EMA technique has considerable advantages over the contact techniques when objects with “rough” surfaces are tested in the automatic mode. The advantages of the EMA technique are due to the features of its electromagnetic channel and feasibility of tuning its parameters in real time.     

Measuring the extraction time of negative ions from the ionization chamber of a static mass spectrometer

A technique for measuring the time of extraction of negative ions from the ionization chamber of the ion source of an MИ-1201“B” static mass spectrometer is described. The time of extraction of SF₆ negative molecular ions equal to ∼(8.5 ± 1.0) μs is comparable to the ion time of flight in the tube of the analyzer.     

Experimental study and evaluation methodology on hard surface integrity

The Taguchi method is adopted experimentally to investigate the surface integrity (surface roughness, residual stress, and thermal damage layer) of hardened bearing steel in hard dry turning, and the validation experiments are consequently performed. It was revealed that the value and effect sequence of optimal hard turning parameter varies with different objectives of surface integrity. However, it is quite difficult to select or determine the optimal combination of hard turning parameters. A hard-turned component performance, which reflects an integrated impact of surface integrity, should be fully recognized to resolve the inherent conflict in the selection process. Based on it, an evaluation methodology composed of four steps is proposed that surface integrity should be evaluated by the service/fatigue life of hard-turned components and therefore turning parameters. It bears significance for super-finish hard turning further application in respect that it provides an integrated approach for hard turning parameter optimization to achieve a superior surface integrity. Funded by the Ministry of Education of China- “985” of international cooperation project “Clean Manufacturing Technology”.     

On the information capacity of the invariant method in the analysis of resampled acoustic-emission streams

Specific features of the diagnostics of a prefracture state using the method of invariants of acoustic emission (AE) are considered. It is shown that “resampling” of a stream by measuring each mth pulse abruptly reduces the randomness of the properties of the initial AE stream. This makes it virtually impossible to determine the degree of hazard of a flaw on the basis of some statistical parameters of resampled Erlang streams (naturally, also including the AE invariant method) even at relatively small recalculation coefficients.     

Error in Measurements of Flaws with the Use of Systems with Coherent Data Processing

In recent years, systems with coherent data processing of the AVGUR series designed by the Ekho+ NPTs have been widely used at Russian atomic power plants for nondestructive testing of pipelines. The paper contains results of an analysis of the effect of practical testing parameters (instability of the acoustic contact, parameters of piezoelectric transducers, etc.) on the quality of the flaw image and the error and accuracy in determining flaw parameters: the coordinates of the flaw depth, height, and length. The errors in determining the flaw parameters in the primary and repeated inspection are distinguished. It is shown that the error reduces in the repeated inspection. The results of comparing the data obtained in destructive and nondestructive testing of austenite welded joints of pipelines from stainless steel 325 × 15 mm in diameter are given.     

Ultrasonic testing of welded joints in pipelines. New techniques and instruments

The paper describes a technique for ultrasonic testing of welded joints in pipelines of small diameters (10 to 530 mm) with thin walls (2 to 10 mm). A highly efficient technique of ultrasonic testing using “chord” transducers with elastic protective covers in combination with general-or special-purpose flaw indicators is suggested. The technique has been practically tested for several years. Possibility of recording results of ultrasonic tests with the help of specialized portable instruments is discussed. Results of practical utilization of the developed techniques and instruments in detecting real defects are given.     

Bayesian reassessment of the number of flaws in a pipeline

A practical method for correcting an estimate of the true number of defects in a pipeline after performing in-tube flaw detection and subsequent verification of measurement results by a second independent verifying instrument is presented. A direct correction method was initially proposed by one of the authors [1]. A more precise method, which is based on the Bayesian procedure, is considered in this study. The problem of predicting the most probable number of true flaws in each interval of changes in the flaw parameters (hereinafter, the flaw depth is considered) is solved on the basis of data from the inspection of detected and actual flaws in a pipeline. These results can be used for the evaluation of the quality of a performed in-tube inspection and the quality of in-tube and verifying instruments, when solving appropriate problems of pipeline reliability (as the input data), and when planning inspections on the basis of risk assessment.     

Reliability of tests using ferromagnetic transducers

The paper considers a technique of magnetic testing using ferromagnetic transducers in which the field intensity gradient is compared with a threshold level. A confidence criterion of tests is formulated, and a flaw detector design is “synthesized” to satisfy this criterion. OOO Mikroakustika     

Structural features of crack formation during corrosion cracking

Stress corrosion cracking (SCC) causes damage to main gas pipelines due to formation and development of cracks on the outer surface of a tube. Prevention of SCC crack development and fracture of a gas pipeline is an important problem of diagnostics that can be solved in various ways. The most effective approach involves systematic use of in-tube nondestructive testing and local testing in shafts, owing to which the position of a flaw and its linear size are determined. The hazard of the flaw (residual life of a tube with cracks) is found and a decision is made about the necessity and methods of flaw repair, such as cutting out the tube, grinding the flaw, and reinsulating the tube surface, and the date of repeated nondestructive testing is set. These measures ensure timely discovery of potentially hazardous flaws and make it possible to take the necessary steps for preventing development of SCC.     

Production monitoring—A proven productivity tool

Production executives in modern factories are concerned with standards, real production and schedule maintenance, and with having early foresight into problem areas. The use of digital computers in the factory has for many years been largely divided between “closed-loop control” and “data processing” (DP), but today there is a growing need for “closed-loop information control” (CLIC). This paper describes a system for implementation of this concept using exclusively industry-standard hardware, and its application within smaller industrial operations rather than the industrial giants (although their need may indeed be greater). For many such smaller companies, production monitoring may be a first venture into CIM. Rather than “control” or “data” being the key, “information” is the cornerstone of the system described. The word “information” conjures up a variety of ideas in its normal use, but a visit to a real factory forces a closer look at its meaning, if the CLIC concept is to be even worth considering. Repeatable and verifiable data sources are very difficult to obtain on the factory floor. Physical compatibility is a real concern, because equipment that operates in the usual controlled DP environment is not usually reliable on the factory floor. The operating conditions demanded by much to today's DP equipment preclude heat, vibration, electromagnetic interference and the generally hostile conditions which are prevalent in many factories. Consequently, any factory-floor system is fraught with unique problems all the way from data capture, through communications, into efficient data structures and meaningful graphic presentation. This paper describes such a system and summarises its effect on productivity as proven by application in several factories in the US and Canada.     

A new approach for molding multi component parts

Injection molding has gained an enormous importance over the last twenty years. This is due both to the development of sophisticated products and to the efforts being generally made to the reduction of product weight specially in automobile industry. Developments aimed at creating innovative products are expected to broaden industrial implementation of their techniques. Establishment then requires the progressive development of existing mold techniques and engineering knowledge. This paper describes a successive process for molding multi component complicated products such as door trim, instrument panel and so on. Using an analytical model, the orthogonal experiment method (Taguchi method) and numerical simulation, an optimal process for simultaneous injection molding with “core-back” and “co-injection” technique is presented to produce such innovative products. Through practical tests, this process was verified in terms of applicability.     

Tube for obtaining crystals in a laboratory furnaces

A model of an air-cooled tube with a number of movable plugs, installed in a laboratory tube furnace is presented. The setup (modular “crystallization shelf-comb”) allows easy regulation and simultaneous crystallization tests of a series of crystallization parameters in crucible columns, enabling rapid acquisition of crystals. The relationship between the crystallization parameters has been derived and numerically analyzed. This method can also be applied in crucible or chamber furnaces.     

Amontons' law at the molecular level

One of the fundamental postulates of friction is that at the microscopic or molecular level, the “real” area of contact is proportional to the load applied over the macroscopic or “apparent” area. This has both theoretical and experimental support and has formed the basis of many theoretical analyses, including an explanation of one of the most basic observations of everyday friction, i.e., that the friction force F is proportional to the load L or weight of the moving object (Amontons' law) where the ratio of F to L defines the coefficient of friction μ=F/L. We have carried out friction experiments between two molecularly smooth non-adhering surfaces under conditions where all the relevant macroscopic and microscopic parameters were directly measured. We find that even at the microscopic level the friction force is proportional to the net applied load and not to the real area of contact. One implication of this finding is that Amontons' law is also obeyed directly at the molecular level and does not emerge indirectly because of some fortuitous correlation between the net applied load and the local contact area or shear strength, as is commonly supposed. A physical model, based on intermolecular forces and thermodynamic considerations, is offered to explain why the friction force is proportional to the net applied load, and why the case of adhering surfaces - where the friction force is found to be proportional to the molecular contact area -is quite different from that of non-adhering surfaces. This revised version was published online in June 2006 with corrections to the Cover Date.     

Restoration of the Magnetic Field of a Cluster of Discontinuity Flaws in a Ferromagnetic Product on the Basis of Minimization of a Smothering Functional

A technique of restoring the magnetic field of a flaw cluster in a tested object is proposed. The possibility of restoring the magnetic field strength and estimating the number and the depth of flaws is demonstrated on the basis of the results of measuring the magnetic field of a flaw cluster in a steel plate.     

A Further Discussion on Trends in the Development of Advanced Manufacturing Technology

This paper is a supplement to “Trends in the Development of Advanced Manufacturing Technology” (Yang and Wu in Chin. J. Mech. Eng., 39: 73, 2003) but delves deeper into it. It first points out the strategic status of manufacturing industry in state development. Then, a detailed analysis is given on the features and trends in the development of advanced manufacturing technology in a total of 12 points from three aspects: “precision,” “extreme,” and “culture” from the aspect of the product itself; “green,” “rapidness,” “saving,” and “efficiency” during the manufacturing process; and “digit,” “auto,” “integration,” “networking,” and “intelligence” in view of the manufacturing method. In addition, it emphasizes that all the above aspects should be based on two base points: “manufacture” and “machinery.” Finally, it puts forth the guiding ideologies for the development of advanced manufacturing technology and the aspects China should give priority to in development, while stressing on the principles of independence, innovation and “human orientation.”     

A pig introscope for inspection of main gas pipelines

Development, design, and experimental testing of a new magnetic in-tube pig flaw detector is considered. An in-tube introscope makes it possible to obtain with photographic accuracy a direct image of the inner tube surface for assessment of internal flaws in pipelines.     

Estimating dimensions of flaws with narrow openings along the beam direction

The problem of flaw dimension measurement along the beam direction is discussed from the viewpoint of the measurement accuracy. Practical recommendation are put forth for estimating dimensions of flaws with small openings, such as incomplete fusions in welded joints, along the beam direction using X-ray photographs.