This study examined two m ethods for producing carbon and glass/polyester composite plates and discussed which one was best based on mechanical properties for different volume fractions, random stacking sequences, and ply angles (using MATLAB's random estim ation program). It also determined the three natural frequencies experimentally and with the aid of ANSYS. Less than 6% separated the experimentally determined natural frequencies from the calculated results. Keywords: composite preparation, random fiber design, natural frequ ency, moderate thick plates. 1. Introduction During the last three or four decades, computer simulations of physical processes of composite materi als have been expanded to very close values to real experimental results .[1][2][3][4][5][6] However, the manufacturing method may exert a variation in the verification of the results due to manufacturing process conditions and environments. This br ief is aimed at examining manufactur ing environmental effect on plate characteristics and evaluat ing the natural frequency for the application in hand (i.e., moderate thick composite plate) . Fiber -reinforced composite materials are continuing to replace t he conventional metals in primary and secondary aerospace structural elements owing to their best mechanical properties Currently not just aerospace companies use composite in most of their work, cars companies, civil construction companies, sport equipment companies, etc. use composite in most of its works and its use efficient and face significant problems. Fiber -reinforced composite materials are continuing to replace the conventional metals in primary and secondary aerospac e structural elements ow ing to their best mechanical propert ies Currently not just aerospace companies use composite in most of its work, cars companies, civil construction companies, sport equipment companies, etc. use composite in most of its works and its use efficient and face not significant problems. The moderate thick plates are widely used in many things such as cars, aircrafts, civil constructions and the use of first -order shear plate theory give very good result in the design and optimizati on of moderate thick plate s and commonly use in all over the w orld because of the behave of the moderate thick plates that make the neglecting of the effect of normal stress that perpendicular to the plate possible. At 1981 Zafer Gurdal et al. [7], dev eloped a programming solu tion using Fortran77 based on linear programming to find the optimal design for composite laminates for buckling constraints. Their work based on few cases to pike one of them as best solution, and they noticed that the linear programming alone and with it s simple form not enough for complex design of composite plates. Seung Jo Kim and Nam Seo Goo, [8] studied in 1992 the use of fuzzy environment to find optimal design of laminated composite plates. Their goal was minimized weigh t design for composite laminate plates. For them the fuzzy environment was satisfy for predesigned plates but with more lamina the process gets harder and need more time. At 1993 T. Y. Kam et al. [9] published their paper that deals with dynamic prog ramming with finite el ement method to find the optimum asp ect ratio for laminated moderate thick composite 2 plates that give maximum stiffness and low weight and find the natural frequencies for the plates. The FEM analysis gave optimization process good to ol of numerical analys is but the need of matrices made the time is not dependent factor in their design. Dynamic programming more powerful of linear programming but it s still ordinary and classic method of optimization and not efficient like other evoluti onary methods of optimi zation. Young Shin Lee et al [10], published their paper at 1994 on optimal design of hybrid laminated composite plates with static and dynamic constraints and take ply angle and ply thickness as design variables. They use a linear programming method an d nonlinear optimization problem for various hybrid rectangular composite plates with arbitrary boundary conditions. At 199 4 C. Huang and B. Kroplin, [11] presented their research that deals with multi -objective function to minimize while satisfying con straints such as the structural defo rmation and the limits on design variables, and they performed the stiffness analysis by the finite element method for optimal design of a rectangular thick and moderate thick laminated plate. For mu ltiobjective function , it was need ignore and cancel term s and not necessary ( according researcher viewpoint), and that make the accuracy approaching to optimum not easy to achieved. At 2001 Pavel Y. Tabakov [12] used improve genetic algorithm to mult i-dimensional design optimization combine with finite el ement method to find best analysis for stacking laminates and show that the stability of evaluation in direct coding less than for binary coding but the first coding much fast in find solution. At 2004 Roberto Brighe nti [13] used genetic algorithm with finite element method to perform the distribution and orientation of the laminates in the composite plates to had best distribution for desire bending load. At 2005 Erik Lund et al. [14], used disc rete material opti mization for laminate hybrid composi te to find optimal design for desired buckling loads. A. N. Bambole and Y. M. Desai [15] published their paper at 2007 that dealed with using a novel 27-node three dimensional hexahedral hybrid -interfa ce finite element model to analyze composite sandwich hybrid moderate thick and thick plates using minimum potential energy principal and optimize the thickness and orientation of laminates for bending in plates with multi -supporting conditions. At 200 7, B. Pluch et al . [16], combined finite element meth od with genetic algorithm to optimize composite hybrid moderate thick and thick structures with variable thickness. M. Kemal Apalak et al . [17], studied at 2007 layer optimization and stacking seque nce using a model of hybrid artificial intelligence m ethod based on a genetic algorithm foundation and accelerated by using artificial neural network wit the the use finite element method as a evaluation technique to find the maximum fundamental frequency. They also ma de a numerical sequence to optimize layer sequences for maximum fundamental frequency using genetic algorithm with evaluation technique that Ritz -based layerwise 2. Composite Plate Components 2-1 The Matrix There is one type of resin used in this r esear ch to construct the models of hybrid composite plates that is: Polyester Resin The use of Polyester resin (NCS 942), that made by SRBS Company. The mixture need to 24 hours or more (according to environmental conditions) to solidification, and the m ixture done by 1 unite volume of har dener to 100 unite volume of resin. 2-2 The Reinforcement 3 The reinforcement of hybrid laminated composite plates should contained at least two different types of reinforcements, so it was use a) Fiber Glass Reinfor cemen t The fiber glass that used was ma de by TGI Company and it was from E -glass type. It is commonly use in Iraqi's markets and consider cheap comparing with other type of reinforcements that used in composite structures manufacturing. Fiber glass has m any a dvantages, such as, good physical properties, high strength to weight ratio, good resistance to chemical agents and it's relatively not costly b) Carbon fibers reinforcement Using carbon fibers as other reinforcement associated with glass fibers to mak e hyb rid composite plates. 2-3 Specimen Preparations For composite plates making, there is many ways to do that and each method or way specify to specific purpose, so the mass production manufacturing differ from laboratory specimen made. Hand lay up is the method that used in this study to make laboratory specimens. The balance that used was made by (Nahuhunda company ) and it calibrated using 1 litter of distill water. After calibration of balance and made it ready for use, it was required to find the density of fibers .volwD= (1) Where d is density, W and V are weight and volume respectively (the densities which have been used in this work are shown in Table (1)) , and that be by first determine of weight to amount of fibers then emerge if in distill water contained in beaker and find out the change in volume before and after fibers emerging and do that to matrix a fter solidification too. The weights of fibers sample and sinker apparatus found using balance made by EHB Adams company Table (1) Densities of reinforcement that used Material Density( Kg/m 3) C/F 1509 G/F 2340 Where C/F was Carbon fiber and G/F was G lass Fiber. Suitable mold is one of impo rtant thing to do to make composite plates, it should be chemical stable for composite materials (no chemical reaction between mold and composite materials) and have good shape ( and that depended on method of making comp osites). To proceed with preparing, first it should heat the mold to remove moisture and the appropriate temperature that used is about 100oC using domestic oven for two minutes, and then (after it cold) coats the inner sides of mold and edges with ins ulator material and waits it to dry. The dray may take 25 to 55 minuets, so the use of low speed of hair dryer to dry molds is saving the time. Other method used to prevent sticking of made plates with molds that using wax. The mold heated and put wax on i ts warm surface, the wax melt and sp read out all over mold surface. The heating done using the oven. The second step is to cut fibers bands with in the range of wanted length, and the third step is to mix resin's components (monomer and poly mer). The mixin g must be good and fast to assure th e full distribution of hardener all over resin material to result good and homogeneous polymer . Then paint first layer of resin inside the mold then spread fibers carefully and press them gently, then put the second laye r or resin and then fibers until hav e the desired composite, That the fourth step. The next step was made by to ways -The first used way 4 The cast of laid composite layers was covered by a 6 mm glass sheet the weight of glass sheet is and pressed by using 50 kilograms of athletics weights and after 72 hours in open atmosphere (the made of samples done in ranged of temperature between (6 o-14o) C at January the thirteen so the range of preparing time changed according to temperature a nd environmenta l conditions). -The second used way Use the experimental device to precede solidification of composite plate. The mold press to make the (Hardener) loss as minimum as possible and to force air bubbles to leave and the pattern us ing insulated p late of glass (6mm) and weights abou t 10 kilograms and put inside sucking chamber to insure evacuation of air bubbles, as well as heating sucking chamber. The heating is by use a secondary container with hot water flow in it from electric bo iler (30 litter water capacity) to control temperat ure. The sucking chamber is a pressure pot connected with fitted 7.5 cm steel tube after removing the one way valve of the pot and sealed with epoxy steel (manufactured by MJM Company), wrapped with rub ber of a tube o f Bike then wrapped by medical gypso na. Use a medical sucker (manufactured by MEDAP, Model P820, West Germany) as a device to induce negative pressure in the pot using -0.2 bar according to its gage see Fig. (1) . Fig. ( 1) Schematic diag ram for sucker device The sucke r operation is put on and off with a timer of 5 on and 5 off minute alternatively to avoid damage in the sucker. The pressure pot put in plastic sunk which is used as a hot bath to keep the pressure pot at temperature (5 0-60) o C. Providing the sunk with t wo plastic taps one above and one bellow to provide a current of hot water flow 150 drops per minute to keep the path hot at (50 - 60)o C for 48 hours. The plastic sunk is covered by double layers of plastic sheet used in agricultural green houses and from a round and below, the plastic sank wrapped with a wool blanket . Use room (2*2 square meter area *3 meter height) provided with a square window (45 cm side length) closed with a glass sheet and fitted with i ndustrial cork use in packing fridges then sealed o f a peace of clothe. The room is warmed by 1000 watt electric heater (manufactured by National company) according the availability of electricity. The lower space of door and key opening filled with ordina ry domestic spo nge. After 48 hours the specimen is ready to extract from mold and that is by easy depending on good coating of insulator and mold shape. The cutting of samples of test was made using angel grinder that manufacture by HORCE Company with u se cutting whee l (100 mm, A -30-S), and drill made b y Reshan company with grinding head. The wasted material is difficult to be calculated because of -manual processing -shattering and spreading of the materials particles . 3. Mechanical Properties Determin ation Sucking Chamber Water Bath The Sucker Water Source Control Valve 5 The tensile test device used in this research made by (TSG) company, and its feature was drawing data on special paper. The strain gage device used associated with tensile test apparatus . The strain gage that used manufacture by omega Compa ny made of Nick el foil and its resistance was 25 oh ms with tolerance around 25 ohms, the calibration done with specific known mechanical characteristics steel specimen in temperature of woke and it was about 25 oC. The cleaning of surface of composite speci men required wi th a special cleaner liquid. After c leaning the envelope of strain gage removed and stamped the gage slowly and takes a few hours to inshore good adhesion then the test began. The nine independent elastic material properties required fo r a 3D lamina b ased analysis were listed as (E 1, E2, E3, G12, G13, G23, υ12, υ13, and υ 23). Preparing a tensile test samples based on ASTM 2003 standard (D638) to evaluate young modulus for all three directions (E 1, E2, E3) The first samples set cut with the direction of fiber to calculate E 1 and a second set cut perpendicu lar to it to calculate E 2. For tensile test the apparatus draw a relation between calculated force and its action representing with elongation, and the original area and length are known so oAP= (2) Where F=force in Newton and A o area in m 2 oLL= (3) Where ΔL= change in length and L o is original length in m So = (4) An assumption used to calculate E 3 that E 2 equal E 3 , so they are both perpendicular to f ibers direction. A strain gages used associated with tensile test by put it in 90 o to tensile direction for calcula ting (ε 2) to find out Poisson’s ratio (υ 12 ), (υ23 ) Where lateral= (5) The value of (υ 12 ) assumed equal to ( υ 13 ) . Equatio n (6) used to find G 12 212 1 45122 1 41 E E EG o+−= (6) Where E 45 is modulus of elasticity to sample cut with angle 45 o from fibers direction. The assumption of equality of G 12 and G 13 used in this work, and G 23 could be found from equation (7) ) 1(2232 23+=EG (7) 4. Vibrational Tests A frame made to achieved simply sup ported case. The frame consist of two sharp knife edges jaws and hold together by four screws Using the results of optimizations programs, the hybrid laminated composite plates constructed, then using home made force vibration device to vib rate the plate with known frequencies and 6 recording the response to fi nd out first three natural frequencies. Use MATLAB Simulink to build wave generation system to generate controlled sin wave goes to the vibrator in addition to build recording system to record the respond wave induced in simply supported plate. The recordi ng done by home made small micro phonic recording system stick on upper middle side of the plate Test done by generate waves and record it to out put files as audio files. The gen erations raise in frequency by 100 Hz every step, and then comparing o utputs using audio analyzer software to find out at what frequency the amplitude of recording files is the largest one, so the frequency is the natural frequency. The estimation of start ing frequency and end frequency based on ANSYS results. 5. Model Fo rmulation in ANSYS Program Building a finite element model requires more of an ANSYS 5.4 use's time than any other part of the analysis. First, job name and analysis title are specified then preprocess is used to define the element types, element real con stants, material properties, and the model geometry. 5-1 Defining Element Types The ANSYS element library contains more than 100 element type. The element type determines among other th ing: 1 - The degree of freedom set 2 - Weather the element lies in two dimensional or three dimensional spac e The element type that used in this work was SHELL99 (see Fig. ( 2) and for more information see ANSYS help) Fig. ( 2) ANSYS 5.4 element t ype that used 5-2 Defining Element Real Constants Element real consta nts are properties that depend on the element type, such as cross -sectional properties of a beam element, for example area, moment of inertia, initial strain, height, etc. 5-3 Defining M aterial Properties Depending on the application, the material propert ies may be: 1. Linear or non -linear 2. Isotropic, orthotropic, or anisotropic 3. Constant temperature or temperature depended. 5-4 Creating the Model Geometric Once the material properties have been defined, then generating a finite eleme nt model –nodes and elements that adequately describe the model geometry. With solid modeling, the geometric shape of model is described, and then instructs the ANSYS program to automatic ally mesh the geometry with nodes and elements, and then control the s ize and shape of the elements that the program creates. 5-5 Apply Loads and Obtain the Solution In this step, the solution processor is used to define the analysis type and analysis o ptions, 7 apply loads, specify load step options, and initiate the finit e element solution . The main goal of a finite element analysis is to examine how a structure or component responds to certain loading conditions. The element used SHELL99 (fore more desc riptions see ANSYS help) . The mathematical model was FSDT with Navier' s solution 6. Results This section deals with experimental and numerical results and discussion which are found out in this thesis as follows: -Mechanical properties results of composite plates experimentally -Optimal design results of composite plates numerically through three programs -Natural frequencies results of composite plates experimentally and numerically with comparison. Tensile strength in the fiber direction a unidi rectional fiber -reinforced composite material deforms as the load incr eases in the following four stages, more or less, depending on the relative brittleness or ductility of the fibers and the matrix: A) Both fibers and matrix deform elastically B) The f ibers continue to deform elastically, but the matrix deforms plastical ly C) Both the fibers and the matrix deform plastically D) The fibers fracture followed by fracture of the composite material 6-1 Mechanical Properties Results As said before, two di fferent ways used to prepare hybrid composite plates, and they discuss ed in chapter four. The test done to samples of plates made by the two mentioned ways and using testing apparatus. In this research three volume fractions used to achieve best mechanical properties and they are 30%, 40%, 50%, and using the necessary method s. 6-1-1 First Method of Preparing Group Taking three volume fractions percentage, gave the following results Table ( 2) Mechanical properties of first method of preparation for 30% volume fraction Glass Fibers \Polyester Carbon Fibers \ Polyester E1(GPa) 23 E1(GPa) 109 E2(GPa) 7.2 E2(GPa) 2.74 E3(GPa) 7.2 E3(GPa) 2.74 υ12 .39 υ12 .32 υ23 .43 υ23 .44 υ13 .39 υ13 .32 G12(GPa) 2.93 G12(GPa) .724 G23(GPa) 2.83 G23(GPa) .916 G13(GPa) 2.93 G13(GPa) .724 Table ( 3) Mechanical properties of first method of preparation For 40% volume fraction Glass Fibers \Polyester Carbon Fibers \ Polyester E1(GPa) 29.73 E1(GPa) 145.8 E2(GPa) 9.06 E2(GPa) 3.46 E3(GPa) 9.06 E3(GPa) 3.46 υ12 .35 υ12 .3 υ23 .4 υ23 .42 8 υ13 .35 υ13 .3 G12(GPa) 3.73 G12(GPa) .96 G23(GPa) 3.62 G23(GPa) 1.213 G13(GPa) 3.73 G13(GPa) .96 Table ( 4) Mechanical properties of first method of preparation For 50% volume fraction Glass Fibers \Polyester Carbon Fibers \ Poly ester E1(GPa) 22.8 E1(GPa) 182.33 E2(GPa) 6. E2(GPa) 4.33 E3(GPa) 7.1 E3(GPa) 4.33 υ12 .38 υ12 .31 υ23 .42 υ23 .43 υ13 .38 υ13 .31 G12(GPa) 2.91 G12(GPa) 1.2 G23(GPa) 2.8 G23(GPa) 2.73 G13(GPa) 2.91 G13(GPa) 1.2 6-1-2 Second method of preparing Table ( 5) Mechanical properties of second method of preparation For 30% Volume Fracti on Glass Fibers \Polyester Carbon Fibers \ Polyester E1(GPa) 24.1 E1(GPa) 111.8 E2(GPa) 7.1 E2(GPa) 2.18 E3(GPa) 7.1 E3(GPa) 2.18 υ12 .32 υ12 .28 υ23 .38 υ23 .4 υ13 .32 υ13 .28 G12(GPa) 3.1 G12(GPa) .896 G23(GPa) 2.72 G23(GPa) .92 G13(GPa) 3.1 G13(GPa) .896 Table ( 6) Mechanical properties of second method of preparation For 40% Volume Fraction Glass Fibers \Polyester Carbon Fibers \ Polyester E1(GPa) 32.133 E1(GPa ) 149.06 E2(GPa) 9.46 E2(GPa) 2.906 E3(GPa) 9.46 E3(GPa) 2.906 υ12 .32 υ12 .28 υ23 .38 υ23 .4 υ13 .32 υ13 .28 G12(GPa) 4.13 G12(GPa) 1.19 G23(GPa) 3.62 G23(GPa) 1.22 G13(GPa) 4.13 G13(GPa) 1.19 Table ( 7) Mechanical properties of second method o f preparation For 50% Volume Fraction Glass Fibers \Polyester Carbon Fibers \ Polyester E1(GPa) 40.16 E1(GPa) 186.33 E2(GPa) 11.83 E2(GPa) 3.633 E3(GPa) 11.83 E3(GPa) 3.633 9 υ12 .34 υ12 .31 υ23 .4 υ23 .43 υ13 .34 υ13 .31 G12(GPa) 5.16 G12(GPa) 1.493 G23(GPa) 4.55 G23(GPa) 1.533 G13(GPa) 5.16 G13(GPa) 1.493 6-2 Vibration Characterist ics Results ANSYS program used to find out the natural frequencies and modes for prepared plates and using the device that discussed in section three , and the results a re: Stacking sequence and Ply angles Table (8) Three Natural Frequencies Numerically and Experimentally Theoretical first three natural frequencies (Hz) Experimental first three natural frequencies ( Hz) 6566.2 10333 10431 6400 10000 10300 7066.7 11165 11182 7000 11000 11300 6566.1 10378 10386 6500 10300 10300 6835.7 10744 10872 6700 10500 10700 6706.5 10527 10680 6400 10200 10300 6835 10746 10871 6400 10200 10300 6835.7 10799 10818 6600 10500 10700 6955.8 10927 11083 6800 11000 11100 6706 10571 10635 6700 10500 10800 The simulations of the three modes of vibration could be seen in Fig. ( 3) Fig. ( 3) Three Modes of Vibration for Rectangular Plate 7. Discussions The experimental results taking for two kinds of plates prepared by two di fferent ways, and tested by tensile test apparatus for each tensile test it took the av erage of five specimens, and other mechanical properties calculate using the equations (5),( 6). It can show from Table ( 2) to (7) that the brittleness increases with th e increasing of the volume fraction and for more discretion the relation between chosen characteristics for first plate preparation method were taken as example (see Figs. ( 4) and ( 5)) 10 Fig. ( 4) Young modulus relation with volume fraction variation Fig. (5) Poisson’s ratio relation with volume fraction variation Second way of preparat ion gave better results than first way, because of negative atmospheric pressure that help evacuate air from lamina. Mechanical properties of second plate preparation method (that been noticeable in Tables (( 2) to (7)) better than first method of preparati on of plates, so the mechanical properties database chosen in optimization programs be of the second plate preparation method. The effect of volume fraction on mechanica l properties obvious from results tables (Table (2) to (7)), the increase in volume fra ction increases the value of strength and also increase Poisson's ratio. Programs data base build on volume fraction 30% so it was more ductile and that give it more fle xibility of response with loads comparing with other volume fraction plates. Excited frequencies, (natural frequencies), are a property of the system. Amplified vibration, called resonance, occurs when a generated frequency is tuned to a natural frequen cy. An excited natural frequency is a resonant condition. Resonance in rotating machine ry is the same as an amplifier in electronics. Therefore, excessively high vibration amplitudes are often encountered. ANSYS program used to identify and calculate natur al frequencies, and mode shapes. A vibrator used to induce natural frequencies in prepa red plates that analyzed using ANSYS as discussed in chapter four. The results showed high values of natural frequencies and that agreed with ref. [18-25]. The difference i n natural frequencies results between experimental and theoretical values about 6%. 9. Conclusions Following are the main summarized conclusions drawn from this paper : 1- It could be seen that the second method of preparing of composite plates was mo re efficient from the first way, and that could be because of the effect of the nega tive atmospheric pressure that make lose of air bobbles more easy and efficient. 2- During putting loads on plates in the first method the layers and fibers moved clusterin g in places, so load distribution on all over plate been unequal and made it more we aken. 3- The difference between the experimental and numerical finding of natural frequencies were less than 6%. The high value of natural frequencies could be noticed, bec ause of the complex 11 composition of plates in the microstructure, so every fiber and even the chain of matrix materials give a special response in its direction and the wide verity of play angle gave its this specialty. 4- The mechanical properties of composite plates are used in this thesis which has been found out experimentally and comp ared with its relevant used in ref. [26], found almost same behaviors.