18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS OPTIMAL DESIGN OF COMPOSITE INSERTS FOR A HYBRID ULTRACENTRIFUGE ROTOR Hak Gu Lee 1* , Jisang Park 1 , Ji Hoon Kim 1 1 Composite Materials Group, KIMS, Changwon, Korea * Corresponding author( hakgulee@kims.re.kr ) Keywords : centrifuge, hybrid composite rotor, composite insert, optimization 1 Introduction 2 Finite element model An ultracentrifuge is essential equipment in 2.1 Structural concept of a hybrid composite bioindustry to separate tiny biogenic substances such as hormones. The equipment should be able to rotor generate the G -force (gravitational force) higher Fig.1 shows the cross-section view of a hybrid than 600,000 ´ g . Among diverse components of an composite rotor for an ultracentrifuge. The rotor ultracentrifuge, a fixed angle type rotor is the most consists of the core, the composite inserts, and the important component that affects the equipment’s composite outer layer. Almost all of the centrifugal performance. forces are sustained by the composite outer layer, in There have been several studies related to rotating which stiff carbon fibers are wound according to the structures. The problem on the stress distribution of circumferential direction. However, the weakest part a rotating isotropic disc with a central hole is a well- is not the outer layer but the core or the composite known example[1]. A rotating anisotropic disc was inserts because of their relatively very low strength. firstly analyzed by Tang, and he derived the analytic If there is no composite insert, the circumferential solutions of the centrifugal stresses[2]. Belingardi stress are concentrated in the point a or b in Fig.1 also considered a rotating anisotropic disc, but where the radial thickness of the core has a constructed approximated solutions[3]. minimum value, and the radial stress are Studies concentrated on designing centrifuge rotors concentrated in the point c in Fig.1 where the are as follows. Hai-jun carried out failure analysis of circumferential thickness of the core has a minimum an isotropic centrifuge rotor, and suggested how to value. optimize the rotor structure[4]. Joe designed a hybrid type composite rotor, in which carbon fiber/epoxy composites were wound around a polymeric core[5]. Among diverse design studies, Joe’s design is one of the most feasible rotors that can be manufactured with low cost. A hybrid composite rotor having a polymeric core experiences stress concentration phenomenon near tube holes that accept sample fluids to be separated. The stress concentration of the core can be alleviated Fig.1. Cross-section view of a hybrid composite by bonding composite inserts into the tube holes. In rotor for an ultracentrifuge. this study, the dimensions of the composite inserts are optimized in order to reduce the stress 2.2 Simplified slice disc model concentration. Using a simplified slice disc model, which give us a more conservative design than a 3-D When rotating, the rotor in Fig.1 experiences shear rotor model does, stress distributions in the core, the stress components s zr and s z q . Since the shear composite outer layer, and the composite insert were stresses transfer centrifugal loads from the bottom analyzed by FEM(finite element method), and then part of the rotor, which is in the higher stress level, found optimal dimensions of the composite inserts. to the top part of the rotor, which is in the lower
stress level, a stress analysis of a simplified slice 2.3 Material properties disc based on the plane stress assumption gives Table 1 shows the material properties of the core, conservative evaluation. the composite insert, and the composite outer layer, The dimensions of the model are as follows. As which are PEI, Kevlar/epoxy composites, and shown in the Fig.1, composite inserts are located not AS4/3501-6, respectively. The material combination parallel to the z-axis, but with the inclined angle q CI is the best one of the previous research that can from the z-axis. Thus, the cross-sectional shape of generate the G -force with the lowest stress level[6]. the composite insert on the r- q plane is the ellipse whose minor radius is the same as the radius of the Table 1 Material properties composite insert and whose major radius is one over Kevlar/ AS4/ PEI cos q CI times the radius of the composite insert. In epoxy 3501-6 this study, the inner radius of the composite insert E 11 76.8 148 Stiffness [GPa] 3.0 was 5 mm. The two variables in this study, the E 22 5.5 10.5 G 12 2.07 5.61 thickness and the inclined angle q CI of the composite Shear modulus [GPa] - G 23 1.40 3.17 insert have the ranges from 1.6 mm to 2.2 mm and v 12 0.34 0.30 from 0 ° to 25 ° , respectively. Poisson’s ratio 0.36 v 23 0.37 0.59 Fig.2 represents FE model to calculate stresses near Density [kg/m 3 ] r 1270 1380 1520 the tube hole. Considering symmetric conditions, we S 11T 1380 53.4 Tensile 105 constructed a 15 ° sliced disc model. The point A in Strength S 22T 27.6 2137 [MPa] Compressive S 22C - - 238 Fig.2 is the position where the maximum G -force Shear S 12 - 49 89 generated. The distance from the rotating axis to the Fiber volume fraction V f - 0.55 0.62 point A is 40 mm. Since the rotating speed is 100,000 rpm, the G-force at A is 447,000 ´ g . The 2.4 Coordinate systems boundary radius between the core and the composite outer layer is 43 mm, and the inner radius of the core As shown in Fig.3, two kinds of coordinate systems is 25.8 mm, i.e. 60% of the boundary radius. The are used in this study, global cylindrical coordinates outer radius of the composite outer layer is 51.3 mm, whose origin is on the rotating axis of the centrifuge which is the optimal dimension of the composite and local elliptical coordinates whose origin is on outer layer suggested by the previous research[6]. the center of the ellipse. Material properties are The boundary conditions of the model are as follows. assigned to the core and the composite outer layer The inner and the outer radius are on the free according to the global cylindrical coordinates, and boundary conditions, and the cutting out edges at q to the composite insert according to the local of 0 ° and 15 ° are on the symmetric conditions. Its elliptical coordinates. Since the composite insert is loading condition is applying centrifugal body forces inclined to the r- q plane of the simplified model, its only. properties should be translated from the ply coordinates of the insert to the local elliptical coordinates of the model. Fig.3. Coordinate systems used in the analysis; Fig.2. Finite element model to calculate stresses near global cylindrical coordinates and local elliptical the tube hole. coordinates.
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