Volume 4, No. 13 (2007)
Articles
STRESS TRIAXIALITY AS FRACTURE TOUGHNESS TRANSFERABILITY PARAMETER FOR NOTCHED SPECIMENS
AKOURRI O., ELAYACHI I., PLUVINAGE G.
The problem of fracture toughness transferability is treated by using the stress triaxiality and by introduction of a new transferability parameter called p. This parameter is a combination of effective critical stress triaxiality (mean value of stress triaxiality over effective distance) and multiplies by a geometrical function. Application of this method has been made on three point bending specimens made in XC 38 steel. Comparison of 2D and 3D approaches is made.
THE INFLUENCE OF THE SHEET THICKNESS ON SPRINGBACK PHENOMENON IN CASE OF A PART MADE FROM TAILOR WELDED STRIPES
ALBUŢ AURELIAN
This paper presents the results obtained by numerical simulation regarding springback phenomenon of a part manufactured from tailor welded stripes. The final shape of the formed part is seriously affected by springback phenomenon. This paper work is trying to prove the important role the metal sheet thickness on the springback effect. The part has different springback values for each material from the welded assembly structure. The influence of the sheet thickness on the tailor welded stripes springback is examined by finite element method using Abaqus Standard for forming process and Abaqus Explicit for springback of the obtained part.
WORKABILITY OF TAILOR WELDED BLANKS
ALBUŢ AURELIAN
The application of tailor welded blanks offers significant potential for reducing the weight of future automobiles and improvements are being made in the development and understanding of the welding process. There are several geometric and internal weld features that make the complete numerical description of tailor welded blank forming challenging. The variation of the experimental formability results found in the literature for tailor welded blanks appears to be large, and a combined theoretical tensile instability and statistical analysis of internal weld porosity may explain at least some of the variation reported.
THE NUMERICAL CALCULUS OF THE FIRE RESISTANCE OF THE STEEL CROSS-BEAMS
ION ANGHEL, IONEL-ALIN MOCIOI, ALECSANDRU PAVEL
Following the tests of fire resistance for different construction materials databases were created using their results, after making possible the development of numerical models experimentally validated. One of these structural models is the zonal program “Ozone”. The present paper underlines the growth of the fire resistance (time to structural failure) of a steel beam from a structure, with a protection of 20 mm of spray vermiculite thick.
QUANTIFICATION OF SPRINGBACK AND ITS REDUCTION BY APPLING AN OPTIMIZATION PROCEDURE
AXINTE C., KOLIOPOULOS T. C.
The present paper presents the experimental results concerning the springback of cylindrical deep-drawn parts. Firstly, the deep-drawing of metal sheets was performed. The geometrical parameters of the resulted cups were then measured and the springback amount was quantified. In order to eliminate or diminish as much as possible the springback phenomenon, an optimization procedure was implemented, which conducted to satisfying results.
FRACTAL DIMENSION AND FRACTURE ROUGH
BABEU TIBERIU DIMITRIE, PETCOVICIU OANA
The description of rough fracture surfaces has been an important challenge for many years. Showing at the fracture surface of a specimen, one realizes that the self-affine geometry of crack faces results from the stochastic nature of crack growth and can treat the fracture surface like as a fractal. Therefore the modelling a crack as a fractal and characterizing it by a fractal dimension has become the focus of research in recent years
EFFECT OF UNDERLOAD APPLIED AFTER AN OVERLOAD ON FATIGUE CRACK PROPAGATION FOR 12NC6 STEEL
BACILA A., MESMACQUE G., ŞERBAN V. A., VODA M.
Overloads and underloads perturb steady state fatigue crack growth conditions and affect the growth rates by retarding or accelerating the growth. Clear understanding of these transient effects is important for the reliable life prediction of a component subjected to random loads. We can imagine that a random loading has a mean stress on a mean magnitude which can be used to determinate the baseline fatigue crack growth rate. The main objective of this research is to analyse the underload effect in fatigue crack propagation after an overload cycle.
EMPHASYSE OF SOME PECULIAR ASPECTS OF A PIPELINE CORROSION DAMGE DUE TO CITADINES WORK CONDITIONS
SEPTIMIU COJOCARU, FAKO RALUCA, IRIMIA IOAN
The paper presents the results of a case study of a failure analysis on a pipeline component serviced about 20 years in an underground structure for oil transportation, between a railway station and a thermal power plant, as result of interaction with urban environmental attack.
FAILURE OF SANDWICH COMPOSITE FOAMS AND MICROSTRUCTURAL ANALYSES OF THEIR BEHAVIOUR
DAN MIHAI CONSTANTINESCU, DRAGOS APOSTOL, MATEI MIRON
In the development of a new generation of advanced sandwich composite materials with special destinations, the mechanical testing is a prerequisite for a better understanding of their behaviour as to be able to calibrate the constants of the material. Without this step any modelling and simulation will be useless in the development of inovative structural components and structures. The refinements of the microstructural analyses are presented hereby for a better understanding of the response of the materials to different loadings.
INFLUENCE OF FRICTION ON THE QUALITY OF INNER THREADS MADE BY PLASTIC DEFORMATION
CRISTEA ION, AXINTE CRINA
An important aspect concerning the processing of metals by plastic deformation is related to the existence of the friction forces between tool and part. The friction forces can determine a great increase of the forming resistance. They are quite hard to measure and consequently, they represent one of the most insecure elements when an analysis of the deformation forces is performed. The friction surface is characterized by microgeometry under dimensional aspect and of distribution law and also under the aspect of asperities deformation. Regardless of the finish degree, the surfaces have asperities that are elastic or plastic deformed or even broken, under the action of a system of forces, velocities and a certain environment.
THE PLASTIC DEFORMATION IN THE MECHANICAL ALLOYING OF THE AMORPHOUS ALLOYS
DRAGOI D. D, DRAGOI A.
The plastic deformation in the cold state generates an increase of the density , of the dislocation and this intensifies the diffusion process in the powder volume and substantially modifies the interfacial characteristics of these by creating some big concentrations of crystalline flows of the type of interstitial allows and vacancies. Knowing the fact that the mobility of the interstitial atoms is bigger than that of the vacancies, these areas can be at a certain moment suprasaturated in vacancies, which could strongly affect the diffusion process.
ABOUT SOME DYNAMIC FRACTURE PARTICULARITIES OF ELEMENTS WITH CRACKS
ION DUMITRU, SECHEI RAMONA, MIHAI HLUSCU
The approach of fracture dynamic of elements with cracks, even today, is experimentally and theoretically difficult. For this reason some particularities of the dynamic stress intensity factor are underlined. The authors present also an experimental method for the determination of KId starting from the observation that this value characterizes the final break at impact fatigue tests. For two test steels the dynamic fracture toughness was found lower that the static one.
CONTINUOUS IMPROVEMENT OF QUALITY
GHELASE DANIELA, DOGARIU CONSTANTIN1, DASCHIEVICI LUIZA
The paper presents some aspects regarding continuous improvement of quality, such as: Kaizen strategy, Deming Cycle PDCA, the „5 S” Method and Quality Circles, methods which can be applied in order to drive a manufacturing process towards excellence.
SEVEN MANAGEMENT AND PLANNING TOOLS
GHELASE DANIELA, DASCHIEVICI LUIZA, DIACONESCU IOANA
Thanks to globalization and rapid advances in technology, today’s manufacturing environment is increasingly competitive. Manufactures need to stay focused on finding new ways to design, produce, sell and deliver products. So, the paper presents seven management and planning tools which promote innovation, communicate information and successfully plan major projects.
FINITE ELEMENTS ANALYSIS AND CRACKING CALCULATION FOR PINION- RACK MECHANISM REGARDING THE DIRECTION MECHANISM
GOANTA VIOREL
In this paper, a finite elements analysis of the pinion-rack mechanism (part of the direction system) is made. Based on the obtained results, a calculation of the lifetime of this mechanism will be made, considering that a micro crack has initiated at the base of the rack’s tooth.
THE INFLUENCE OF THE DISPERSION OF PARTICLES IN THE VICINITY OF A CRACK
GOANTA VIOREL
In the matrix of a material which contains micro cracks particles with properties different than the ones of the main material can be dispersed. In this project the way in which the stresses in the vicinity of a micro crack vary, reported to the presence nearby of some inclusion particles with different properties. The purpose of this analysis is to find a method to stop the propagation of a crack in the stressed material reported to the direction of the crack.
UNIFORM PRESSURE LOADED SUPER FERRO CEMENT MADE PLATES BENDING ASSESSEMENT
HRENIUCANDV., MODIGA, M., DIMACHE, A.
The submitted paper presents the author`s contribution in a super mortar ferro cement development and testing. Following a general view on ferro cement as such, particular approaches are made on so called "super ferro cement" in general and specifically on the material developed and tested. The material being entirely original, extensive experimental tests were performed, including the plates bending assessment. Both the testing equipment and the test schedule were domestically developed and manufactured. Owing to the composite’s complex internal structure, a FEM analysis was also performed for stresses assessment and layout, analysis based on the experimental data and whom results (computed deflection figures in particular) matching closely the measured ones.
ANNULAR PLATE WITH SIMPLE LEANED CONTOURS, UNDER THE ACTION OF AN UNIFORM DISTRIBUTED PRESSURE
RADU I. IATAN, CARMEN T. POPA
The paper proposes to establish the expressions of the angular and linear deformations of a circular and annular plate, having simple leaning on the external contours, under the action of a uniform distributed pressure on one face (fig. 1). We propose, too, to determine the calculus relations of the radial and annular stresses, in the domain oh the elastic solicitation. To reach this purpose we take into account two variants of study.
SOLICITATION STATES IN THE ANNULAR AND SIMPLE LEANED PLATES ON THEIR CONTOURS, UNDER THE ACTION OF SOME RADIAL BENDING MOMENTS (I)
RADU I. IATAN, CARMEN T. POPA
In the composition of the mechanical equipments for the industrial processing of the substances, some annular plates, having the role of separation of the working spaces, or fixing of some specific constructive elements can be met. For dimension or verify the respective geometries, one of the analyze variants is that which hypothetical devises the adjacent elements and establish the equilibrium connection loads. For an annular plate, having the simple leaned contours, the effects about the deformation and stresses state of some connection radial bending moments are presented in one first variant in this paper. In this sense, in line, the simple leanings are assimilated with the effects of some normal and uniform distributed forces at the medium surface. It is mentioned, too, that the solicitation of the plate is considered in the elastic domain, which is specific to the construction material.
STRESSES STATES IN RIBBED AND CIRCULAR PLATES
RADU I. IATAN, CARMEN T. POPA
In this paper is presented the analyses with finite elements as well as the experimental obtained results of a circular plate having radial ribs. We had been made mentions for 0, 3 and 0, 4 MPa pressures, in the both cases making the respective comparisons.
NUMERICAL AND EXPERIMENTAL STUDY OF THE STRESS STATE AND THE POSSIBILITY OF CRACK INITIATION IN A FASTENING ELEMENT OF A HYDROAGGREGATE
ILIESCU N., ATANASIU C., PASTRAMĂ Ş. D., BACIU FL.
In this paper, a combined numerical and experimental study on the stress state of a fixing element from the rotor of a hydroaggregate is presented. The photoelastic and chromoplastic methods, together with finite elements analyses were used. The study is focused on the areas with stress concentration, zones where cracks may develop. These cracks may propagate, leading to the failure of the structure. The moment of crack initiation was determined experimentally, on chromoplastic models loaded until failure. Conclusions are drawn regarding the numerical validation of the experimental models and the possible brittle failure due to crack propagation.
SOME ISSUES ON THE SHEAR MODULUS DETERMINATION BY USING THE 10° OFF-AXIS TENSILE TEST
BOGDAN LEIŢOIU, MARIAN MAREŞ
The shear properties of long-fiber reinforced composite materials can be studied on the basis of some tension tests, on the condition, for the reinforcement, to be oriented at an certain angle in respect with the load direction. The most frequently used, at this aim, are the values of 10° and ±45°. The present paper focuses on the experimental results obtained from some 10° off-axis tensile tests, on a unidirectional carbon/epoxy composite. One can consider that the resulted shear modulus values are consistent with those obtained, for the same material, using the Iosipescu shear test.
ON THE USE OF IOSIPESCU SHEAR TEST FOR CHARACTERIZING SOME COMPOSITE MATERIALS
MARIAN MAREŞ, BOGDAN LEIŢOIU
The test methods that were proposed, for studying the shear properties of composite materials, are numerous, but varied and controversial. As a consequence, there is no method globally accepted at this aim. Nevertheless, one can accept that some methods are considered more suitable for nonhomogeneous and nonisotropic materials. In that meaning, the test method that was created by professor Iosipescu is one of the main shear tests, at this moment, and as a result it was adopted as a ASTM Standard test method. This paper presents some experimental results, obtained by applying that method on some carbon/epoxy fiber reinforced composites
CORROSION AND SHIP HULL ULTIMATE STRENGTH
MIRCEA MODIGA, ALINA DIMACHE, HRENIUC VICTOR, ANDREAS IOANOU
For steel construction and marine structure in particular, the corrosion can be one of the collapse cause, due to excessive reduces of strengths areas and implicit decrease of ultimate moment, accomplished with the fatigue crack and progressive fracture evolution. At present, corrosion rata estimation has an empirical character, therefore the simplified models is use. The variables in frequently used corrosion models have probabilistic character. The means and the standard deviation for plate’s thickness in different corrosion phases of linear and parabolic-linear models are presented in the paper. On the base of linear model are done some results for hogging ultimate bending moment at a bulk-carrier in different stages (ages) of corrosion.
LIMIT MOMENTS UNDER COROSSION AT BULK-CARRIERS
MIRCEA MODIGA, LEONARD DOMNISORU, ALINA DIMACHE
On the base of linear corrosion model are done some analysis results of limit moments (Initial Yielding Bending Moment, Ultimate Yielding Bending Moment, Ultimate Bending Moment in Hogging and Sagging conditions) at a bulk-carrier hull girder transverse section in different stages (ages) of corrosion. For wide plate is obtained the load-end shortening (average stress-average strain) values, needed for the used ULTIM code, which considers the effects of welding initial deflections, residual stress and vertical shear force.
THREE DIMENSIONAL STRESS FIELD AND STRESS INTENSITY FACTOR CALIBRATION FOR A CENTRAL CRACKED PLATE
MOREIRA P. M. G. P., PASTRAMĂ Ş. D., P.M.S.T. DE CASTRO
The purpose of this work is to obtain accurate three dimensional stress field and intensity factor solutions for a plate with a central crack using the Finite Element Method. For the comparison with the three dimensional solutions, further to reference values given by the literature, two dimensional Finite Element Analyses were performed. The study reveals a good agreement between the present three dimensional analysis and the literature solutions, especially in the mid-plane of the plate. The plane strain behaviour near the crack front and the variation of the opening stress are discussed, together with the possible use of a simple formula for the three dimensional stress intensity factor using the two dimensional value.
ASPECTS CONCERNING THE OPTIMIZATION OF THE TECHNOLOGICAL PROCESSES
ION NAE, MARIUS GABRIEL PETRESCU
The fabrication technology of a product may satisfy the demands imposed by the construction, may assure the realization of the production plan in the conditions of using the existent material base (machine-tools, SDVs, semi-product goods etc.), respecting certain economic conditions (cost, work productivity) and social ones. The paper presents the way to determine the cutting regime parameters values for the turning operation; there is made a comparative analysis of the values determined using the analytical calculus method and the automatic one.
ASPECTS CONCERNING THE SOFTWARE APPLICATIONS IN ORDER TO DETERMINE THE ECHNOLOGICAL SYSTEMS RELIABILITY
NEACŞA A., STOICA D. B.
Within the paper there are presented the reliability problems specific to the technological systems, a programme that allows making certain applications simplifying the traditional mathematics device and getting closer quickly to solution taking into consideration its economic aspect in the working conditions. There are presented some general considerations regarding the method followed by an example regarding the estimation of the drilling bit reliability modeled like a serial technological system.
USING THE FINITE ELEMENT METHOD FOR CONSTRUCTIVE OPTIMIZATION OF THE ELASTIC ELEMENT COMPRISED IN A MECHANIC DYNAMOMETER
PASCU ADRIAN, GALAFTION SOFONEA, MARCU FRĂŢILĂ
This paper presented a constructive optimization for the the elastic element comprised in a mechanic dynamometer, using the finite element method. The purpose of this paper is the determination of the optimal geometrical configuration thus the difference between the specific deformation on the outer surface and the specific deformation on the inner surface to be minim under the condition of satisfying the structure resistance.
THE BASE PHILOSOPHY OF AN AVAILABLE WORKING SERVICE REGARDING THE PETROCHEMICAL TECHNOLOGICAL EQUIPMENTS
ALECSANDRU PAVEL, TOADER GAUREANU
There are grounded the security factor in comparison with destruction/damage time by creep and comparison with creep resistance limit. The association of those two security factors and corresponding numerical analysis are standing out the residual availability of running time under circumstances related to technicaland technological industrial reliability/security.
CALCULATION PRINCIPLES REGARDING THE WEAR OF SHAFT-SLIDING BEARING COUPLING
PETRE IVONA, TACHE CARMEN
The present paper deals with the calculation of wear for a shaft-sliding bearing coupling, trying to point out the factors that influence the wear of the coupling.
THE INFLUENCE OF THE ASYMMETRY COEFFICIENT WITH NEGATIVE VALUES (R<0) ON THE FATIGUE CRACK GROWTH RATE
GHEORGHE PINTILIE, ALBUŢ AURELIAN, ZICHIL VALENTIN
The crack propagation speed is an important parameter used to predict the life time of a part or a mechanical structure. Hence, in the last 50 years, many researchers have tried to explain and to create a mathematic model able to describe the phenomenon of fatigue crack initiation and propagation. In our days, the influence of the asymmetry coefficient having negative values, R, on the crack growth rate is considered an important issue. This paper presents theoretical aspects considered as basics for the NASGROS 5.0 software and the obtained results.
BEM – BOUNDARY ELEMENTS METHOD USED AT THE STUDY OF STRESS CONCENTRATORS (CUTS-OFF) AT ROTATIONAL DISKS IN AXIAL-SYMMETRIC THERMAL REGIME PART I: BEM – THEORETICAL CONSIDERATIONS
GHEORGHE N. RADU, IOANA SONIA COMĂNESCU
The present paper presents the theoretical and experimental method for determination the deformations and the stability loss of disk stressed by an axial-symmetric field, variable according to disk radius and thickness, superposed with a field of membrane tensions given by the revolution movement. The experimental results confirm theoretical hypothesis.
BEM – BOUNDARY ELEMENTS METHOD USED AT THE STUDY OF STRESS CONCENTRATORS (CUTS-OFF) AT ROTATIONAL DISKS IN AXIAL-SYMMETRIC THERMAL REGIME PART II – THE INFLUENCE REVOLUTION-TEMPERATURE AND EXPERIMENTAL RESULTS
GHEORGHE N. RADU, IOANA SONIA COMĂNESCU
The present paper presents the theoretical and experimental method for determination the deformations and the stability loss of disk stressed by an axial-symmetric field, variable according to disk radius and thickness, superposed with a field of membrane tensions given by the revolution movement. The experimental results confirm theoretical hypothesis.
BEM – BOUNDARY ELEMENTS METHOD USED AT THE STUDY OF STRESS CONCENTRATORS (CUTS-OFF) AT ROTATIONAL DISKS IN AXIAL-SYMMETRIC THERMAL REGIME PART III – EIGEN VALUES PROBLEMS AT DISKS
GHEORGHE N. RADU, IOANA SONIA COMĂNESCU
The present paper presents the theoretical and experimental method for determination the deformations and the stability loss of disk stressed by an axial-symmetric field, variable according to disk radius and thickness, superposed with a field of membrane tensions given by the revolution movement. The experimental results confirm theoretical hypothesis.
SOME FAILURE MODES OF POLYLITE 440-M888 POLYESTER RESIN REINFORCED WITH RT300 ROVING FABRIC SUBJECTED TO TENSILE LOADINGS
ROSU DORIN, GOIA IOAN, VLASE SORIN, TEODORESCU HORATIU
The paper presents some failure modes occured in tensile tests of Polylite 440-M888 polyester resin specimens reinforced with RT300 roving fabric, specimens that have been cut in warp direction of the reinforcement. Tensile tests results are also presented. The first failures of the specimens took place in the form of inter-fibers brake at a strain of about 0,03.
OPTIMIZATION OF PRODUCTION PROCESSES WITH THE HELP OF KANBAN METHOD
ROTARU ANA
The materials’ weight in the production cost, as compared to the salaries, increased in the last years from 2:1 to 3:1. As a consequence, the production control focuses on a more economical management of this element, all the more so as it carries along restrictions and disturbances external to the manufacturing. Kanban is a method applied to the materials transfer, among various working positions, in JIT system. It provides (ensures) the order control of the performed activities and stocks. Within the framework of this article one will try a presentation (description) of this method, of its performance, of the advantages and of the limits of this method.
VALUE STREAM MAP INSTRUMENT OF LEAN MANUFACTURING SYSTEM
ROTARU ANA
The map of the value stream is a diagram where are included all the necessary steps to cover by the information flow and materials from the receiving of a control to the product’s delivery. Lining (tracing) the value stream map can be a repetitious process but can also be a requirement (necessary condition) for improvement. Within the framework of this article one will make a description of this instrument of Lean Manufacturing system, of the stages necessary to its accomplishment and one will emphasize the information that can be obtained after its accomplishment.
THE INFLUENCE OF THE TECHNOLOGICAL ELEMENTS ON THE ROUGHNESS OF THE SURFACES PROCESSED THROUGH PLASTIC COLD FORMING
SÂRBU IONEL, PRUTEANU OCTAVIAN, PARASCHIV DRAGOS, CARAUSU CONSTANTIN
In the paper we presented the experimental results regarding the influence of the working parameters: the deformation force P [MPa], the forming feed A {mm/min}, the speed of rotation of the piece V [rot/min], on the roughness of the surfaces processed through cold plastic forming.
THE RTR ROBOT PATH OF MOTION, WHEN THE TRANSLATION COUPLING LAW IS SINUSOIDAL
GABRIELA SĂVUC, DANIELA FLORESCU, FLORESCU IULIAN, MIHAI STANCU
This paper studies the path of motion of the characteristic point of the RTR robot, when at the coupling level the working laws are replaced by the sinusoidal laws, used mathematical model of the quaternion.
ASPECTS REGARDING THE EVALUATION OF THE UNCERTAINTY IN THE DETERMINATION OF THE RESIDUAL STRESS THROUGH THE HOLE DRILLING METHOD
ULERIU DORINEL
Knowing the uncertainty result measurements of the trials is of a fundamental importance for the laboratories, their clients and for all the institutions which use these results in a comparative way. The competent laboratories know the performance of their methods of trying and the uncertainty associated with the measurement’s results. This work presents the working way which includes the steps that have to be taken to evaluate the uncertainty at the determination of the residual stress through the hole drilling method. Here are presented the concepts that are the basis of the measuring uncertainty evaluation, parameters for which uncertainty is to be estimated, sources of uncertainty and influence of factors on the measuring uncertainty of the hole drilling method and their quantification.
MANAGEMENT OF REMANENT TENSIONS: ASPECTS ON CALCULATIONS OF LAYERS RESISTANCE AND RIGIDITY, TAKING INTO ACCOUNT THE REMANENT TENSIONS; MEASUREMENT TECHNIQUES
ULERIU DORINEL
The work presents the way of calculation of resistance and settlement for the layers of the engineering components, taking into account the remanent tensions, calculations which have at its base the principle of the critical energy. Meanwhile, the work presents the tens metric technique of perforation, the ultrasonic and X rays diffraction technique used to determine the remanent tensions.
SUCKER ROD FATIGUE BEHAVIOR ANALYSIS
ULMANU VLAD, MIHAELA CĂLŢARU, MARIUS BĂDICIOIU, GH. ZECHERU, GH. DRĂGHICI
In order to identify the best hot rolled steel producer for sucker rod manufacture, a research was performed in order to compare the mechanical strength and fatigue properties of sucker rods manufactured from steel bars delivered by two producers. The fatigue tests were performed on round test specimens on rotating bending and on full size sucker rod, using an axial fatigue test machine. The fatigue behaviors of both materials and sucker rods are practically the same.
THE LINEAR AND ANGULAR LOGARITHMIC STRAIN AND THEIR UTILIZATION IN THE CONTINUUM MEDIA PROBLEMS
UNGUREANU VIOREL
The focus of this paper is the presentation of linear and angular components of logarithmic strain tensor determination that are useful in the description of large plastic deformation. The definition of logarithmic strain is obtained from law of energy transformation and conservation. The linear and angular components of logarithmic strain tensor are compared with the conventional strain. The differences between the conventional and logarithmic (true or natural strain) are presented in some obtained diagrams. The components of logarithmic strain are useful in the experimental analysis of strain field in the cold forming processes, in the mechanical characteristics of the materials determination, and other application in the mechanics of continuum media.
THE ANALYSIS OF THE DURABILITY WITH THE VARIATION OF THE TEMPERATURE TO AN ECCENTRIC AXIAL SOLICITATION FOR R=0.5 IN THE STEEL 10 TiNiCr 175
VÂLCU ROŞCA, PROCA VICTOR, MIRELA GHIORGHIAN
The durability of a first part submitted to fatigue during the service is a very important parameter in the safety of a mechanic structure’s functioning. This thing is necessary both the environmental temperature and to low temperatures. For a stainless steel, mark 10 TiNiCr 175 fatigue attempts were made through eccentric straightening, with the asymmetry coefficient R=0.5, on the temperatures T=293 K, T=253 K and T=213 K. For the low temperatures (253 K and 213 K) we mounted on the attempt machine a frigorific chamber cooled with liquid nitrogen. During the attempt we have kept in mind the variation of the crack’s length ai and the durability Ni. The samples tested had type CT, with lateral notch. We calculated according to the ASTM norm the stress intensity factor ?K at the top of the crack. The fracture is produced after the mode I of solicitation, by opening the crack. Through a numeric calculation program we have then calculated and then drawn graphics for the durability N in report to the calculated length a, respectively in report to stress intensity factor N(?K).
VARIANTS OF ANALYSIS OF THE PROPAGATION RATE OF THE CRACK TO THE AXIAL CYCLIC SOLICITATION FOR THE VARIATION OF THE WORK TEMPERATURE
VÂLCU ROŞCA, MIRELA GHIORGHIAN
Through this work, it is proposed the study of the increase rate of the crack da/dN, for a solicitation to fatigue through eccentric monoaxial straightening, in a sample made of steel for boilers and recipients mark R 520. There are analyzed variants for the cracking rate: the standardized polynomial method, the method of Paris’ formula, the secant method and the simple polynomial method. The samples have been solicited with the asymmetry coefficient R=0.3, for the following temperatures: 293 K, 253 K and 293 K. The equipment used was a hydraulic installation with one pulsator, with the possibility of regulating the asymmetry coefficient R. For low temperatures was mounted on the machine a frigorific precincts cooled with liquid nitrogen. During the attempt we have noted the variation of the crack’s length ai and the numbers of solicitation cycles Ni with the data obtained and the solicitation tasks we have calculated the stress intensity factor ?K and the tension ? at the top of the crack. With the parameters calculated above we passed to tracing some graphics for the cracking rate in report to SIF ?K, V(?K), the rate in report to the durability N, V(N), respectively, in report to the tension ?, V(?). We have drawn these curbs for the three attempt temperatures.
THE SPECIAL FEATURES OF USING FRACTURE ARRESTORS IN NATURAL GAS TRANSMISSION PIPELINES
GH. ZECHERU, GH. DUMITRU, GH. DRAGHICI, DAN CHEŢAN, ALIN DINIŢĂ, LAŢA ILIE
This paper presents the features of using fracture arrestors in order to increase the safety of gas transmission pipelines operation. The paper presents the main causes of operating failure, fracture behavior, the anticipated failure methodology, the criteria for determining the usage necessity and the lay-out of the fracture arrestors for this important category of pipelines.
INFLUENCE OF COMPOSITE WRAP REPAIRS ON THE STRUCTURAL INTEGRITY OF PIPELINES
GH. ZECHERU, GH. DUMITRU, GH. DRĂGHICI, ALIN DINIŢĂ, LAŢA ILIE
This work presents the particularities of repairing pipelines by means of coatings made of composite materials, the solution suggested by the authors for the finite element analysis of the influences of the repairs performed with this kind of coatings on the structural integrity of pipelines and the characteristics of the materials the efficiency of the repairs performed with this kind of coating depend on.