Volume 3, No. 9 (2003)

Articles

INVESTIGATION ON THE STRAIN VARIATION DURING TENSILE TEST OF TAILOR WELDED SHEETS BY USING THE IMAGE ANALYSIS METHOD
BRABIE GHEORGHE, CHIRIŢĂ BOGDAN, CHIRILĂ CIPRIAN

The quality of the tailor welded blank is very important for the successful of the forming operation. The behavior of the TWBs can be determined by applying different methods. The present paper investigates the behavior of tailor welded blanks by analyzing the strain variation during tensile test - parallel and normal -of tailor welded sheets made by joining similar metals by applying the image analysis method.

View article Article
ANALYSIS OF THE STRESS-STRAIN CURVES EXPERIMENTALLY DETERMINED FOR TAILOR WELDED SHEETS
BRABIE GHEORGHE, CHIRIŢĂ BOGDAN, CHIRILĂ CIPRIAN

The parts manufactured by metal sheets stamping can be made in homogeneous or heterogeneous materials (tailor welded blanks). Between these two kinds of materials there are differences in their structure and hence many differences in their behavior will result during forming operations. The differences in the structure and behavior of these materials require different conditions in the testing methods used to determine their mechanical characteristics. The present paper analyses the main particularities of the testing methods as a consequence of their different structures in the case of stress-strain curves determination.

View article Article
THE ANALYZE OF THE DEEP BORING PROCESS, USING FINITE ELEMENTS METHOD
BUNEA MARIAN *, NESTIAN GABRIELA **

The paper presents an analysis model of the cutting forces that appear at the deep boring with the help of Finite Elements Method (F.E.M.). The essence of the finite elements method consists in the transformation of continuous spectrum, in which is developed a certain phenomenon, into a points unit, named nodes, interconnected between them on rules that reflect the properties of the continuous medium. The conditionings of the domain, examined in connection with the outward, are transferred in accordance with the nodes unit. It is analyzed, as a calculus example of the proceedings of deep boring, considered as applied to the semi-products of which are made the artillery barrel, the material being that for which the analysis was made by the finite elements method.

View article Article
THE EFFECTS OF THE INTERNAL AND EXTERNAL FACTORS CONCERNING MOISTURE BEHAVIOUR OF THE COMPOSITE MATERIALS
CERBU CAMELIA*, CURTU IOAN*, ROŞU DORIN**, SUCIU SIMONA*

Moisture absorption in polymer composites is influenced by internal factors (fibre type, fibre fraction and its orientation) and external factors (relative humidity and temperature). In this paper, the authors report the influence of the internal and external factors on the moisture absorption characteristics (equilibrium absorption and diffusion coefficient), of permeable (jute-epoxy) and impermeable (glass-epoxy) composites.

View article Article
RESEARCH REGARDING THE DELAMINATION AT LIGNOCELLULOSE COMPOSITE ENFORCED WITH GLASS, FLAX OR CARBON FIBER
CURTU IOAN, REPANOVICI ANGELA, CIOFOAIA VASILE

The multilayered composite materials generate a negative phenomenon called delamination, that is the weak adhesion within layers at different mechanical strains. The paper approaches theoretical and experimental research made of lignocellulose composites (layers of fibres and gummed chips of wood) and enforced within the marginal areas with one or more layers of carbon, glass or flax fibres. The theories TSAI-WU, HOFFMANN supported by the finite element method, enhance the study of distribution and the intensity of shear stresses within layers. The aim is to minimise the stresses in the light of the following considerations: positioning the enforcing layers; layers thickness related to the composite plate thickness; the variation of fibre-chips of wood weight proportion is to be considered as well.

View article Article
EXPERIMENTAL RESEARCH ON THE METROLOGICAL RELIABILITY OF THE MECHANICAL DEVICES FOR PRESSURE MEASUREMENT. PART I - EXPERIMENTAL INSTALLATION FOR ACCELERATED TESTS
COMĂNESCU IOANA, RADU GHEORGHE

In order to subject the mechanical devices for pressure measurement to accelerated tests, one has been conceived an experimental installation which allows the simultaneous testing of three manometers and also the check of the indications, after testing, with a standard pressure gauge.

View article Article
EXPERIMENTAL RESEARCH ON THE METROLOGICAL RELIABILITY OF THE MECHANICAL DEVICES FOR PRESSURE MEASUREMENT. PART II - STUDIES ON ACCELERATED LIFE TESTS OF THE MANOMETERS
COMĂNESCU IOANA, RADU GHEORGHE

Accelerated life testing of products and components is used to get information quickly on specific lives, life distributions, failure rates, mean lives and reliabilities. Accelerated testing of manometers is achieved by subjecting the test units to application and operation pressure levels that are more severe than normal or use pressure levels, in order to shorten their lives or their times to failure. If the results can be extrapolated to the use pressure levels, they yield estimates of the lives and reliabilities under use pressure.

View article Article
MODULAR DESIGN IN DIMENSIONAL AUTOMATIC CONTROL SYSTEMS
CRISTEA LUCIANA, REPANOVICI ANGELA, CIOFOAIA VASILE, CURTU IOAN

Inscribed within the general tendency to reach efficient technological procedures, the preoccupation to improve the automatic systems' structure and performances aimed at analyzing not only the mechanical systems but also the technological procedures in the domain. The paper reveals a series of results obtained following some researches achieved in case the automatic control systems are restructured. Based on theoretical research, the paper presents different modes to increase the functional performances of the analyzed systems by using modular structures.

View article Article
ON THE ANALYTICAL METHODS CONCERNING TRANSVERSAL IMPACT ANALYSIS OF THE ISOTROPIC BEAMS
DOGARU FLORIN, POPA SORIN, TERBES NARCIS

In this paper we present an investigation about analytical method used for analysis beams subjected to transversal impact. The methods are: energy balance models, spring-mass models and complete models. We consider 8 numerically example. Two from this example are presented in the literature: impact on a half-space by a steel ball [1, 4] and Timosheiiko`s example, impact on a simple supported beam [1, 2, 3, 5]. The result were compared using all three method presented.

View article Article
THE RESISTANCE OF A SUBTERRANEAN CONCRETE STRUCTURE USED FOR SUSTAININGS
ILINCIOIU DAN, ROŞCA VÂLCU

For the mining galleries from the sites with soft rocks, highly resisting sustainings are required; the cost of exploitation is diminished if built-up concrete elements should a mathematical analysis model for the resistance of a circular sustaining meant for the galleries within the coal-extracting mines in the zone of Oltenia (Romania).

View article Article
DETERMINATION OF THE BEST CONFIGURATION FOR A STRATIFIED PLANE PLATE WITH MECHANICAL AND THERMAL LOAD
JIGA GABRIEL, HADAR ANTON, PASTRAMĂ ŞTEFAN DAN

The paper presents a computer program, made by the authors and used for studying the stress state in a plate manufactured from a fiber reinforced stratified composite material. Both mechanical and thermal load are considered. The program allows the optimization of the composite material configuration, by establishing the configuration of the optimal orientation of the fibers in the matrix, in the case where the total number of plies with the same orientation is imposed.

View article Article
UPON CALCULUS OF AERODYNAMIC DRAG FORCE OF THE KINETICS PROJECTILES
NASTASESCU VASILE

This paper presents some theoretical and practical aspects regarding finite element method applied in exterior ballistics. Using of this modern calculus method allows us to solve many aspects of exterior ballistics, specially geometric and cinematic characteristics of the projectile moving. One of the main problem in exterior ballistics is calculus of the aerodynamic drag force. This force can be easily calculated by FEM. Next to it the corrections due to atmosphere factors (wind, temperature) or firing from mobile platforms can also be easily calculated.

View article Article
CONSIDERATIONS REGARDING THE INFLUENCE OF THE WORKING PARAMETERS ON THE ROUGHNESS OBTAINED BY THE SUPERFINISHING PROCESSING OF 41MoCr STEEL
NESTIAN GABRIELA*, PRUTEANU OCTAVIAN*, DAN G. RADU*, SOLOMON IULIAN*, BUNEA MARIAN**

Superfinishing, known as well as vibrofinishing, is a technological method for processing metallic pieces through chip removal, and more, of fine finishing with abrasive. This paper presents the influence of working parameters for superfinishing processing’s on the roughness surface.

View article Article
THEORETICAL AND EXPERIMENTAL CONSIDERATIONS OVER BOUNDARY ELEMENT METHOD (BEM) - A STUDY OF DISKS, PRESENTING CUTS-OFF AND BEING IN A ROTATIONAL MOVEMENT AND THERMAL REGIME. PART I - THEORETICAL CONSIDERATIONS
RADU GHEORGHE, COMANESCU IOANA

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.

View article Article
THEORETICAL AND EXPERIMENTAL CONSIDERATIONS OVER BOUNDARY ELEMENT METHOD (BEM) - A STUDY OF DISKS, PRESENTING CUTS-OFF AND BEING IN A ROTATIONAL MOVEMENT AND THERMAL REGIME. PART III - EXPERIMENTAL RESULTS
RADU GHEORGHE, COMANESCU IOANA

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.

View article Article
THREE-COMPONENT, STRAIN GAGE BASED MILLING DYNAMOMETER DESIGN AND MANUFACTURING
RAVEICA IONEL, ALEXANDRU MARIN

In this study, a dynamometer design and manufacturing, Strain Gage based, three components, computer linked, were carried out to measure cutting forces in milling. Strain gages bonded on the octagonal rings have been used (or sensing of the force signals. The analogue force signals obtained from three-channels have been amplified and converted into digital signals via a data acquisition card and recorded in a computer. To test the dynamometer, deformo-milling operation has been made. It has been observed that, the cutting forces recorded synchronously from the tests have corresponded to the calculated values.

View article Article
EXPERIMENTAL RESEARCH ABOUT AN INERTIAL MECHANICAL SYSTEM
REPANOVICI ANGELA, CURTU IOAN, CRISTEA LUCIANA, CIOFOAIA VASILE

An inertial mechanical system is considering containing a bearing rotor with two wheels placed on it, and four elastic lamellas on each with weights on their ends (extremities). A 45° displacement is between the two wheels. Such installations do not produce moments of rotation or mechanical work like the electrical engines actually do.

View article Article
RESIDUAL STRESS MEASUREMENT METHODS FOR SHEET METAL
SCHNAKOVSZKY CAROL, CHIRILĂ CIPRIAN

This paper proposes to present the Methods of Measuring Residual Stress in Components. The purpose of this review is to provide an overview of some of the recent advances in the area of residual stress measurement and act as a summary document to aid technique selection. The intention is to provide advice and guidance on some of the issues associated with the measurement of residual stress. The results of a Bacau University survey of current interests and expertise in residual stress measurement are presented, together with guidelines on technique selection and some advice on quantifying the measurement uncertainty and accuracy. The physical limitations of the various techniques currently used are also summarized. The work present a variety of techniques were mentioned including hole drilling, X-ray and neutron diffraction, layer removal, magnetic, ultrasonic, Raman and they are ranked by their popularity below.

View article Article
DETERMINATION OF SPRINGBACK PARAMETRS BY SIMULATION OF THE FORMING PROCESS IN THE RECTANGULAR DRAWPARTS MADE IN TAILOR WELDED SHEETS
SCHNAKOVSZKY CAROL, CHIRIŢĂ BOGDAN, CHIRILĂ CIPRIAN, AXINTE CRINA

Springback is a phenomenon that seriously affects the quality of parts made in metal sheets by forming processes. This phenomenon occurs after the pressing force is removed and the part is extracted from the die. After the part extraction its shape will suffer certain distortions whose size depends on different factors. The present paper is an investigation concerning the determination by simulation of springback parameters in the case of a rectangular part made in tailor welded sheets.

View article Article
A STUDY OF SAFTY DOUBLE BELT GUIDE ASPECTS UNDER STRETCHING
SECHE ION*, PODOREANU AUREL*, CIOFOAIA VASILE**, CURTU IOAN**

This paper analysis the tension and deformation state of the safety belt double belt guide. We tried to determine the most suitable material to be used and the stability and dimensions in the regions that concentrate the stresses. The analysis of the stress state is realized by using the finite element method (FEM) in linear states. International traffic safety law regulates the fracture force for the safety belt double belt guide. Solicitation conditions similar to the ordinary safety belt functioning regime for the double belt guide are being statistically analyzed, by using a set of 10 double belt guides randomly selected out of 100 pieces lots. The breaking model is applied on every studied piece, special attention being taken to the stress concentration zone both experimentally and with the finite element method. The obtained results were used to enhance the shape design and the manufacturing technology.

View article Article
THE TENSOR OF LOGARITHMIC STRAINS AND ITS COMPONENTS
UNGUREANU VIOREL

The focus of this paper is the determination of linear and angular components of logarithmic strain tensor used for the description of large plastic deformation. The components of logarithmic strain are useful in the experimental determination of strain field in the cold forming processes, and in the mechanical characteristics of the materials determination.

View article Article
AN EFICIENT METHOD FOR THE RESIDUAL STRESS MEASUREMENT OF SHEET METAL FORMED PARTS
UNGUREANU VIOREL

The strain gage hole drilling method is the most widely used residual stress measurement method. However, for sheet metal formed parts this method is less suited because of small thickness of the sheet metal and, generally, non-uniform stress distribution in the thickness direction. Consequently, for residual stress measurement is proposed a method based on trepanning of small round pieces from formed part and strain determination by digital image analysis. Also, using digital image analysis, the field of displacements and strain in analyzed area may be determined.

View article Article
ABOUT THE OPTIMUM DESIGN OF AUTOFRETTAGED CONTAINERS
UNGUREANU VIOREL

The focus of this paper is the formulation of an optimization technique for the design of the autofrettaged containers taking into account the mechanical characteristics of materials and a maximum internal pressure. The relationship for the determination of outer diameter or radius of a autofrettaged high-pressure container as a function of mechanical characteristics of materials used and maximum working pressure was established. With a computer developed code, a process ofpre-stressingcan be simulated and the initial and working stresses in a container can be quantitatively estimated and graphically represented.

View article Article