Volume 2, No. 7 (2001)
Articles
ABRASIVE GRAIN GEOMETRY - A DETERMINING FACTOR OF WORKING PRESSURE MAGNITUDE IN FLUID JET CUTTING
DEACONESCU ANDREA, DEACONESCU TUDOR
The paper presents the modeling of pressure erosion jet processing, starting from the hypothesis of a conical shape of abrasive grain tips. Assuming a linear variation of the contact pressure between the grain and the part, the relationship for the computation of the pressure to be supplied by the working installation is determined.
NUMERICAL AND EXPERIMENTAL DETERMINATION OF THE STRAIN STATE BETWEEN TWO PLANE ELEMENTS
DINU GABRIELA
In this paper there is solved the problem of the surface contact between a rectangular plate and an elastic foundation, proposing a methodology for calculating the displacements of the points on a contact surface.
ELASTIC DEFORMATION OF MECHANICAL FACE SEAL RINGS
CAZACU MIRCEA-DIMITRIE
One presents a mathematical method to study the elastic deformations of mechanical face seal rings under the action of temperatures, pressures and centrifugal forces, the only able to offer information on its deformations, which appear only in running of a mechanical face seal. The obtained results are very important taking into consideration the value of micron order of the clearance between the two rings and give a theoretical explanation of the negative influence of its varied working regime. The method permit the increase of mechanical face seal reliability by the study of the influence of geometry and the materials of two rings in contact with the fluid film with different hydrodynamic properties.
RESEARCHES REGARDING THE INFLUENCE OF THE CONTACT ZONE DEFORMATIONS FOR MACHINES TOOLS ACCURACY
DINU GABRIELA
The paper presents a study made for estimating the contact zone deformation between the support keys of a machine tool and its foundation and the way these can considerably influence the processing accuracy, in certain working positions. The demonstration was performed on a horizontal milling and boring machine, equipped with two beds on the foundation, one for the column and one for the cross slide, for which reason the deformations can reach significant values.
UPON DESIGN OPTIMIZATION OF BAR STRUCTURES
GAVAN MIRCEA, NICOLAE CONSTANTIN
Bar systems are particularly suited for topology optimization in the true sense of this word, meaning that direct topology variation, like introduction of new members, connecting nodes, supports, removal of the same entities or simply changing the position of nodes are the first changes the designer of such structures has in mind when looking upon an optimal situation. The paper presents some aspects met during design optimization of bar structures related to aircraft engineering and the practical considerations, which followed.
EXPERIMENTAL INVESTIGATIONS ON THE STRAIN STATE IN THE FRAME SIDE MEMBERS OF A SEMITRAILER DUMP
NICOLAE ILIESCU, ATANASIU COSTICĂ, GAVAN MIRCEA, MARIN SANDU
The paper presents the results of a static and dynamic study, undertaken with the strain gauges technique on the frame side members of a semitrailer dump, in which any fatigue cracks were identified. In order to stop the cracks propagation, a reinforcing solution was adopted. To evaluate the efficiency of these modifications, the experimental measurements were performed.
NUMERICAL SIMULATION OF AN IMPACT PROBLEM
NASTASESCU VASILE
This paper presents some theoretical and practical aspects regarding to the impact phenomena calculus using finite element method. Some material models, some equation of state models and others practical aspects are also presented. Next to these aspects failure in materials and its simulation is also presented. Conclusions and remarks that close this paper are very useful for a right approaching of the impact calculus by finite element method.
REMARKS UPON MODELLING OF THIN-WALLED BEAMS
NICOLAE CONSTANTIN, ANGHEL VIOREL, IANCU FLORIN
Thin-walled beams are the background of all light structures. At the beginning, in the first half of the previous century, they were used only in the aircraft industry. Later on, as other dedicated concepts and technologies, they spread to other fields, especially transportation means of all kind. Meanwhile, practical situations imposed continuous development in modeling techniques, aimed to better follow the actual structures. The paper presents comparative results obtained for analytical, numerical and experimental models of representative thin walled beams with open and closed section, with practical conclusions for design activities.
OPTIMIZATION OF COMPOSITE STIFFENED PANELS
NICOLAE CONSTANTIN, GAVAN MIRCEA
Thin-skinned fibre reinforced composites exhibit poor behaviors in compression and bending. Wrecking the excellent performances proved in tension and in plane shear. In order to counterbalance this quite natural tendency present at all thin shells, there are two ways of action: creating stiffened panels or sandwich materials The paper presents, in the frame of the first structural option, some results obtained for stiffened composite panels loaded with lateral pressure and some considerations based on a study concerning the buckling and post buckling behaviors of similar panels subjected to axial compression.
BEHAVIOUR OF SOME STEELS USED FOR THERMAL-ENERGETIC EQUIPMENT, WHEN SUBJECTED TO VARIABLE LOADS AT ELEVATED TEMPERATURES
PALIHOVICI VALERIAN, COMANDAR CORNELIU, AMARIEI NICUSOR
The cyclic action of the stresses, during turbine functioning in variable regime, enhances material decay especially in the stress concentrating areas where fatigue life is severely compromised. The paper presents some contributions regarding the behaviour of some high resistance steels, used for thermal-energetic equipment, when subjected to variable loads at elevated temperatures.
FINITE ELEMENT ANALYSIS OF STRESS MITIGATION TECHNIQUES AS APPLIED TO WELDED STRUCTURES
PILIPENKO ARTEM
Finite element models for the 3D thermo-mechanical analysis of stress- reducing techniques applied to the welded plates have been developed. This publication includes analysis of both purely mechanical and thermo-mechanical methods, Based on the 3D FE model, several stress-mitigation techniques have been investigated. The effectiveness of the methods has been demonstrated on the welded 20mm thick steel plates.
EVOLUTION OF ANGULAR DEFORMATION OF THICK PLATES IN THREE-ELECTRODE SUBMERGED ARC WELDING PROCESS
PILIPENKO ARTEM
The three-electrode submerged arc welding (SAW) is a specially developed technique for long joints of relatively thick plates. The process examined here is used in shipbuilding on 20mm thick plates. The high heat source power (totally approx. 80kW.) allows completing the joint in one run. This paper demonstrates the 3D FE model for thermal-stress analysis of three-electrode SAW process. The main subject of this investigation is monitoring and interpretation of the development of the out-of-plane deformation.
ELASTIC STABILITY OF THE THIN DISKS DUE TO THE TEMPERATURE AND ROTATION STRESS FIELDS PARTI: FINITE DIFERENCES- THEORETICAL STUDY
RADU GHEORGHE, COMĂNESCU IOANA, RADU GABRIEL
The present paper presents the theoretical method for determination the deformations and the loss of stability of the disk stressed by an axial symmetric thermic field, variable according to disk radius and thickness, superposed with a field of membrane tensions given by the rotational motion. The experimental results confirm the theoretical hypothesis.
ELASTIC STABILITY OF THE THIN DISKS DUE TO THE TEMPERATURE AND ROTATION STRESS FIELDS PART H: THE TEMPERATURE EFFECTS. EXPERIMENTAL DETERMINATIONS
RADU GHEORGHE, COMĂNESCU IOANA, RADU GABRIEL
This paper presents both the experimental installation by means of which we can record the deformation and induced stress at thin disks which are in rotation and in axial thermal radiation, and the experimental determination methodology. We particularly insist with the electronic elements conceived and materialized with a view to determination of temperature distribution in real time for disk radius.
THE RIGIDITY OF THE CYLINDRICAL COVERS, WITH WELDED RADIAL RTOS
IATAN RADU
Appealing to "the orthotropical structures theory", this paper establishes the calculus expressions of the neutral surface position and the cylindrical bending rigidity, for a cylindrical cover with welded radial ribs. In this study, the influence of the welding seams above the values of the mentioned sizes is taken into debate. The demonstration is conducted on two practical cases.
ASSESSMENT VARIANTS OF THE RIGIDITY OF THE CIRCULAR PLANE PLATES, WITH RADIAL RIBS, WELDED ON A FACE
IATAN RADU, POPA CARMEN
The paper presents a series of specific cases for the establishment of the neutral area and of the circular plates rigidity, with radial and welded ribs, having variable height. The inferred relations take into account the coefficients of admission, which characterize the orthotropical structures. The illustration praises the favorable effect of the ribs and of the welding seams, above the rigidity of the circular stiffed plates.
NUMERICAL STRESS AND STRAIN ANALYSIS FOR ANNULAR PLATE SECTORS WITH UMFORMLY DISTRIBUTED LOADS
SANDU ADRIANA, MARIN SANDU
The last decades, in the stress and strains analysis of elastic structures, the finite elements method (FEM) is preferred others numerical methods as boundary elements method or finite differences method. This fact can be explained by the great performances of general programs for finite element analysis (FEA), offered by specialized software producers, in this moment. However for solving less complicated problems, as the bending of the plates, also the finite differences method (FDM) can be used. In this case, specialized programs can run even on less performant computers. In this paper, the results obtained by finite element and finite differences analysis are compared, in order to distinguish the specific advantages of each method.
DEFORMATION AND FORCE TRANSDUCERS FOR TESTING IN AERONAUTICAL INDUSTRY
DAN-MIHAI STEFANESCU
In the present paper there is a comparative analysis of several elastic elements types for deformation and force transducers. A study of requirements involved in the design of high-performance transducers is performed. Some personal achievements of the large range of specific applications in the aerospace field, as for instance the facility for the landing gear testing in the specialized company in Bacau, are presented in this work.
THE ENHANCED MARCINIAK TYPE TESTING DEVICE AND FORMING LIMIT DIAGRAM DETERMINATION
UNGUREANU VIOREL, PINTILIE GHEORGHE, JUDELE ADRIAN
Some characteristics of enhanced Marciniak device useful in the experimental determination of forming limit diagram are presented. Combined with the utilization of CCD camera for image capture of the tested specimen and the image analyzing software, the forming limit diagrams and forming limit stress diagram may be obtained. Because in the area of biaxial stretching some materials show unexpected behavior, a series of elliptical punches was designed. Also, in order to extend the forming limit diagram in the region of negative minor principal stress, a special "X" shaped punch was used.
THE SHARE STRAIN TEST OF SHEET METAL SPECIMENS
UNGUREANU VIOREL, JUDELE ADRIAN
A technique for share strain test of sheet metal has been developed allowing the equivalent stress-equivalent strain curve determination. The effect of some experimental parameters over the equivalent work-hardening curve of sheet metal specimens has been determined for some materials and compared to those obtained at the same strain rate in uniaxial tension. The validity of proposed method is examined at different point of view and is concluded that the method is quite reliable and can be used in the study of forming behaviour of sheet metals.
THE ELASTO-PLASTIC BEHAVIOUR OF SHELLS
VASILESCU ŞERBAN, TALLE VIRGILIU
In the paper are presented some theoretical aspects regarding the elasto- plastic behavior of shells. Some plastic mechanisms are analyzed and the corresponding limit pressure is calculated.
DEFORMATIONS IN THIN CYLINDRICAL SHELLS LOCALLY LOADED WITH TEMPERATURE
VASILESCU ŞERBAN, TALLE VIRGILIU
In the paper is presented an original algorithm for strength calculation of thin cylindrical shells loaded with temperature. The results obtained are presented in a unitary form which allows the determination of stresses and displacements in the cylinder.
STUDY OF SOIL ARTIFICIAL COMPACTION USING THE FINITE ELEMENT METHOD
BIRIŞ SORIN
The compaction of soil can be defined as an increase in its dry density and the closer packing of solid particles or reduction in porosity. Compaction can result from natural causes, including rainfall impact, soaking, internal water tension and the like. Artificial compaction occurs under the download forces of machines which are usually of short duration in the case of many vehicles. Within the framework of this paper, an original study is presented for the compaction of soil analysis using the finite element method in the case of an U-445 tractor and a SM-445 bulldozer.
CREEP BEHAVIOUR ESTIMATION FROM HARDNESS TESTS
COMANDAR CORNELIU, PALIHOVICI VALERIAN, AMARIEI NICUSOR
Indentation creep is defined as time dependent motion of a hard indenter into a solid under constant load and temperature. Two different models have been developed for indentation creep: the model developed by Mulhearn and Tabor, and model developed by Atkins. The paper presents the research of the authors concerning to creep behavior of an alloy steel, the installation for long time hardness testing at high temperatures and graphics of the results obtained.
NOTCH IMPACT TESTINGS ON AMBIENT AND COLD CHARPY CARBON STEEL TEST-PIECES
AMARIEI NICUSOR, PALIHOVICI VALERIAN, COMANDAR CORNELIU
Notch impact test are widely used in industry as acceptance checks. They are relatively simple and are easy and rapid to conduct. This type of test has the advantage of revealing a tendency to brittleness that is not revealed by either a standard tensile test or hardness test. Not all materials fail in the same manner and the type of fracture that occurs may be either brittle or ductile. The type of failure that occurs is largely dependent on the nature of the material and its condition, but failure is also affected by other factors, including the type of stressing, the rate of application of stress, temperature and environment. The paper presents and discusses the results obtained at the impact bending tests, performed at room temperature and at -30°C, on specimens prepared from tubes used within a network for transport and distribution of natural gases.