《纺织复合材料》课程参考文献（3-D textile reinforcements in composite materials）05 Manufacture and design of composite grids

156 3-D textile reinforcements in composite materials Davis)and McDonnell Douglas Astronautics Company [1]have been pioneering the use of aluminum and later composite grids principally for the fairing and the interstage cone of missiles.W.Brandt Goldsworthy of Rolling Hills,California,pioneered not only pultruded but also filament wound grids.He first proposed this for the Beechcraft Star Ship in the 1970s. Recently,Burt Rutan of Scaled Composites in Mojave,California,built the fuselage of a corporate jet out of composite grids.The USAF continues to explore composite grids with new applications.The McDonnell Douglas Handbook [1]has been updated with the use of composite materials by Chen and Tsai [2]and by Huybrechts [3].The modeling used in this work draws heavily from these earlier publications.The software developed by these authors is instrumental in the analysis and figures used throughout the current effort. It has been recognized by many people that filament winding would be an optimal method for manufacturing grids if the composite tows could be guided by some soft tooling.Grids are assembled by carving out slots or grooves in a rubber tool. 5.3.1 Assembly methods 2502 We believe that new approaches can improve performance and,at the same time,lower cost.A variation in the grid assembly is the configuration of the rib intersection or joint.Three possible joints are shown in Fig. 5.5. ne SLOTTED JOINT STACKED JOINT TRIG JOINT (in carpentry) (a bird cage) bonded or interlaced 5.5 Three types of joints in a grid.The slotted joint is not recom- mended.Stacked and TRIG joints can be produced more easily and have better properties

Davis) and McDonnell Douglas Astronautics Company [1] have been pioneering the use of aluminum and later composite grids principally for the fairing and the interstage cone of missiles. W. Brandt Goldsworthy of Rolling Hills, California, pioneered not only pultruded but also filament wound grids. He first proposed this for the Beechcraft Star Ship in the 1970s. Recently, Burt Rutan of Scaled Composites in Mojave, California, built the fuselage of a corporate jet out of composite grids. The USAF continues to explore composite grids with new applications. The McDonnell Douglas Handbook [1] has been updated with the use of composite materials by Chen and Tsai [2] and by Huybrechts [3]. The modeling used in this work draws heavily from these earlier publications. The software developed by these authors is instrumental in the analysis and figures used throughout the current effort. It has been recognized by many people that filament winding would be an optimal method for manufacturing grids if the composite tows could be guided by some soft tooling. Grids are assembled by carving out slots or grooves in a rubber tool. 5.3.1 Assembly methods We believe that new approaches can improve performance and, at the same time, lower cost. A variation in the grid assembly is the configuration of the rib intersection or joint. Three possible joints are shown in Fig. 5.5. 156 3-D textile reinforcements in composite materials 5.5 Three types of joints in a grid. The slotted joint is not recom￾mended. Stacked and TRIG joints can be produced more easily and have better properties. RIC5 7/10/99 8:04 PM Page 156 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:30:51 AM IP Address: 158.132.122.9

Manufacture and design of composite grids 157 Slotted joint grids The traditional slotted joint grids are shown on the left in Fig.5.5 and are most frequently used in carpentry.Slots are cut into ribs and assembled. The disadvantages of this design include: cost of machining slots, difficult assembly of many ribs having multiple slots, low rib strength introduced by machined slots and notches. low grid stiffness and strength from imperfect fit at slotted joints. We understand that Composite Optics Incorporated of San Diego,Califor- nia,used [/3 laminates as the rib in order to increase the rib strength.The use of laminates for ribs,however,degrades the grid stiffness by a factor of 3 from unidirectional ribs.It is therefore our opinion that slotted joint grids should remain as a popular technique for carpenters and cabinet makers. poo Stacked joint grids 1S: We believe that the stacked joint grids shown in the middle in Fig.5.5 can be as effective as slotted joint grids and can be simpler to manufacture.An Tontun for tries To build stacked rid,longitudinal and hoop or r example of stacked joint grid is the bird cage,which has been in existence members are stacked.Members run on separate planes,similarly to the plies in laminate.There are at least two variations.The longitudinal members (longis)are pultruded,filament wound or made in a female mold by blow molding.The cross members (circs)can be skins applied by filament winding to form a circular or conical grid or shell. The longitudinal tubes may be fan-shaped,for example,and serve the same purpose as a sandwich core between the inner and outer filament wound skins.Although winding can also have a helical pattern if an increase in shear rigidity is desired,such a process increases the cost of manufac- turing over pure hoop winding.The longitudinal and cross members may be fully or partially populated,i.e.the longis do not have to be placed adja- cent to one another.The hoop wound plies can be continuous or discon- tinuous like bands or rings.An example of a ring reinforced cylinder is shown in Fig.5.6. Other examples of a stacked grid include cross-members made by molding or vacuum infiltration.A multi-hole bar or ring through which lon- gitudinal rods or tubes are threaded and bonded forms a bird cage-like structure.There are many possible configurations for different applications. Stacked grids,however,are currently limited to orthogrids.Isogrids,for example,are difficult to make because ribs in three levels must be stacked and joined

Slotted joint grids The traditional slotted joint grids are shown on the left in Fig. 5.5 and are most frequently used in carpentry. Slots are cut into ribs and assembled. The disadvantages of this design include: • cost of machining slots, • difficult assembly of many ribs having multiple slots, • low rib strength introduced by machined slots and notches, • low grid stiffness and strength from imperfect fit at slotted joints. We understand that Composite Optics Incorporated of San Diego, Califor￾nia, used [p/3] laminates as the rib in order to increase the rib strength. The use of laminates for ribs, however, degrades the grid stiffness by a factor of 3 from unidirectional ribs. It is therefore our opinion that slotted joint grids should remain as a popular technique for carpenters and cabinet makers. Stacked joint grids We believe that the stacked joint grids shown in the middle in Fig. 5.5 can be as effective as slotted joint grids and can be simpler to manufacture. An example of stacked joint grid is the bird cage, which has been in existence for centuries. To build a stacked grid, longitudinal and hoop or cross members are stacked. Members run on separate planes, similarly to the plies in laminate. There are at least two variations. The longitudinal members (longis) are pultruded, filament wound or made in a female mold by blow molding. The cross members (circs) can be skins applied by filament winding to form a circular or conical grid or shell. The longitudinal tubes may be fan-shaped, for example, and serve the same purpose as a sandwich core between the inner and outer filament wound skins.Although winding can also have a helical pattern if an increase in shear rigidity is desired, such a process increases the cost of manufac￾turing over pure hoop winding. The longitudinal and cross members may be fully or partially populated, i.e. the longis do not have to be placed adja￾cent to one another. The hoop wound plies can be continuous or discon￾tinuous like bands or rings. An example of a ring reinforced cylinder is shown in Fig. 5.6. Other examples of a stacked grid include cross-members made by molding or vacuum infiltration. A multi-hole bar or ring through which lon￾gitudinal rods or tubes are threaded and bonded forms a bird cage-like structure. There are many possible configurations for different applications. Stacked grids, however, are currently limited to orthogrids. Isogrids, for example, are difficult to make because ribs in three levels must be stacked and joined. Manufacture and design of composite grids 157 RIC5 7/10/99 8:04 PM Page 157 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:30:51 AM IP Address: 158.132.122.9

158 3-D textile reinforcements in composite materials Pultruded longi's Round. Fan-shaped 5650602红 Inner cylinder +-+ 299互 Retaining circ's k-Spacing→ 5.6 A stacked grid with round or fan-shaped longitudinal members sandwiched between inner and outer windings. (sL6-LS-IL)Kus -Helical pattern Interlacing filling the gap Tooling positioned 1/ 5.7 A filament wound cylinder made by the TRIG process.Left: tooling from contoured tubes.Right:wound interlacing fills the V-shaped grooves for grid strength. Interlaced joint grids For the interlaced grid,the thin wall tubes,again,are the starting compo- nents.The filament wound tubes with all-hoop plies provide maximum stiff- ness for the final grid.The tubes are sliced to a contour that fits a mandrel. They are then positioned as tooling on the mandrel.This is shown on the left in Fig.5.7.The V-shaped gaps between tooling are filled with interlac- ing tows,as shown on the right.The interlacing tows carry sufficient resin to bond the tooling and interlacing together to form a solid,continuous rib. The interlacing gives superior strength to the grid.The tooling becomes part of the finished grid and provides high stiffness to the grid.Although tooling contributes to the grid stiffness,it terminates at the rib joints.The disconti- nuity is small relative to the length of the rib.The effect on the grid stiff- ness is small

Interlaced joint grids For the interlaced grid, the thin wall tubes, again, are the starting compo￾nents.The filament wound tubes with all-hoop plies provide maximum stiff￾ness for the final grid. The tubes are sliced to a contour that fits a mandrel. They are then positioned as tooling on the mandrel. This is shown on the left in Fig. 5.7. The V-shaped gaps between tooling are filled with interlac￾ing tows, as shown on the right. The interlacing tows carry sufficient resin to bond the tooling and interlacing together to form a solid, continuous rib. The interlacing gives superior strength to the grid.The tooling becomes part of the finished grid and provides high stiffness to the grid. Although tooling contributes to the grid stiffness, it terminates at the rib joints. The disconti￾nuity is small relative to the length of the rib. The effect on the grid stiff￾ness is small. 158 3-D textile reinforcements in composite materials 5.6 A stacked grid with round or fan-shaped longitudinal members sandwiched between inner and outer windings. 5.7 A filament wound cylinder made by the TRIG process. Left: tooling from contoured tubes. Right: wound interlacing fills the V-shaped grooves for grid strength. RIC5 7/10/99 8:04 PM Page 158 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:30:51 AM IP Address: 158.132.122.9

Manufacture and design of composite grids 159 Significant cost savings can be obtained when the interlacing is filament wound with one helical winding angle.Having a V-shaped groove along a helical pattern would allow high-speed winding.That would further reduce the cost of assembly. 5.3.2 Features of grids We have discovered theoretically that grids are more efficient if the ribs are tall and thin.This process,identified as the tooling reinforced interlaced grid (TRIG),yields a high geometric definition for the ribs and also high grid stiffness.Several current interlacing and fiber placement processes use rubber or foam as guide and tooling.These processes do not produce the high definition and stiffness that the TRIG process does. The advantages of composite grids are derived from the availability of mass-producible rods and tubes,and from the final assembly by filament winding.This winding process is one of the most advanced and widely avail- able processes.Curing is done at room or elevated temperature.Debulk- ing,bagging and autoclaving are not required.With this process the cost of making a grid can be close to the cost of materials,not many times the cost. Assembly by adhesive bonding in the case of some stacked grids can also be cost effective. 争 Although the stiffness of composite grids is nearly equal to that of lam- inates,the strength is many times higher.This is because unidirectional ribs do not fail by microcracking or delamination,but by loss of strength or buckling.Where foamed tubes are used,the grids will have superior damping and acoustic properties that cannot be matched by metallic struc- tures.Composite grids are also more resilient.There is no permanent defor- mation upon unloading.Thus composite grids do not dent or crumple like sheet metals. While the advantages of composite grids are high strength and low cost, there are also disadvantages.As of now,grids can only be made in simple geometric shapes.Such a limitation is often imposed by filament winding. Circular and conical shells are the easiest.Spherical shells can be done using the TRIG process.But doubly curved or concave surfaces are not suitable for grids.Bolting is not recommended without local reinforcement. Finally we recommend that grids be designed to carry all the loads.Skins are present for functional reasons only:in sandwich panels the skins carry the load. 5.4 Mechanical properties of grids We wish to describe the stiffness and strength of grids and compare them with comparable properties of laminates

Significant cost savings can be obtained when the interlacing is filament wound with one helical winding angle. Having a V-shaped groove along a helical pattern would allow high-speed winding. That would further reduce the cost of assembly. 5.3.2 Features of grids We have discovered theoretically that grids are more efficient if the ribs are tall and thin.This process, identified as the tooling reinforced interlaced grid (TRIG), yields a high geometric definition for the ribs and also high grid stiffness. Several current interlacing and fiber placement processes use rubber or foam as guide and tooling. These processes do not produce the high definition and stiffness that the TRIG process does. The advantages of composite grids are derived from the availability of mass-producible rods and tubes, and from the final assembly by filament winding.This winding process is one of the most advanced and widely avail￾able processes. Curing is done at room or elevated temperature. Debulk￾ing, bagging and autoclaving are not required. With this process the cost of making a grid can be close to the cost of materials, not many times the cost. Assembly by adhesive bonding in the case of some stacked grids can also be cost effective. Although the stiffness of composite grids is nearly equal to that of lam￾inates, the strength is many times higher. This is because unidirectional ribs do not fail by microcracking or delamination, but by loss of strength or buckling. Where foamed tubes are used, the grids will have superior damping and acoustic properties that cannot be matched by metallic struc￾tures. Composite grids are also more resilient.There is no permanent defor￾mation upon unloading. Thus composite grids do not dent or crumple like sheet metals. While the advantages of composite grids are high strength and low cost, there are also disadvantages. As of now, grids can only be made in simple geometric shapes. Such a limitation is often imposed by filament winding. Circular and conical shells are the easiest. Spherical shells can be done using the TRIG process. But doubly curved or concave surfaces are not suitable for grids. Bolting is not recommended without local reinforcement. Finally we recommend that grids be designed to carry all the loads. Skins are present for functional reasons only: in sandwich panels the skins carry the load. 5.4 Mechanical properties of grids We wish to describe the stiffness and strength of grids and compare them with comparable properties of laminates. Manufacture and design of composite grids 159 RIC5 7/10/99 8:04 PM Page 159 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:30:51 AM IP Address: 158.132.122.9

160 3-D textile reinforcements in composite materials 5.4.1 Stiffness of quasi-isotropic laminates It is useful to compare the stiffness of laminates and equivalent grids.The simplest comparison is that between isotropic laminates and isogrids.Lam- inates become quasi-isotropic with equally spaced ply orientations of [/3], [/4],[/5]and so on.Similarly isotropy of the grid is assured when the three ribs are spaced 60 apart.There are closed-form solutions of the plane stress stiffness components [4]. The quasi-isotropic invariants are linear combinations or the ply stiffness components shown below: 3 1 u=g0.+0m)+40,+0s U=3 1 3 10 [5.1 3 u=80a+0m)+40w+22s The quasi-isotropic Young modulus,Poisson ratio and shear modulus of the laminates are functions of the invariants: diu [5.2] where D=U2-U2. On the other hand,when the degree of anisotropy of a composite ply increases to the upper limit,the only dominant stiffness component is the longitudinal Young modulus E.The matrix-related components become vanishingly small.Then the invariants above approach: 4-君u-g6-g 3 [5.3 The resulting engineering constants of this limiting quasi-isotropic laminate are: =G-古D=g,- [5.4 The mathematical results in the last equation may be explained physi- cally by viewing a laminate having three independent plies of equal thick- ness.The effective stiffness is equal to of the unidirectional stiffness because each ply occupies of the total laminate thickness.Having the same stiffness in 60 intervals,the laminate becomes isotropic.This can be shown by averaging the transformed stiffness components

5.4.1 Stiffness of quasi-isotropic laminates It is useful to compare the stiffness of laminates and equivalent grids. The simplest comparison is that between isotropic laminates and isogrids. Lam￾inates become quasi-isotropic with equally spaced ply orientations of [p/3], [p/4], [p/5] and so on. Similarly isotropy of the grid is assured when the three ribs are spaced 60° apart.There are closed-form solutions of the plane stress stiffness components [4]. The quasi-isotropic invariants are linear combinations or the ply stiffness components shown below: [5.1] The quasi-isotropic Young modulus, Poisson ratio and shear modulus of the laminates are functions of the invariants: [5.2] where D = U1 2 - U4 2 . On the other hand, when the degree of anisotropy of a composite ply increases to the upper limit, the only dominant stiffness component is the longitudinal Young modulus Ex. The matrix-related components become vanishingly small. Then the invariants above approach: [5.3] The resulting engineering constants of this limiting quasi-isotropic laminate are: [5.4] The mathematical results in the last equation may be explained physi￾cally by viewing a laminate having three independent plies of equal thick￾ness. The effective stiffness is equal to 1 –3 of the unidirectional stiffness because each ply occupies 1 –3 of the total laminate thickness. Having the same stiffness in 60° intervals, the laminate becomes isotropic. This can be shown by averaging the transformed stiffness components. n iso iso iso [] [] [] === = 1 3 1 8 1 8 1 3 2 , ,, G ED E E E xx x U EU EU E 145 xxx 3 8 1 8 1 8 === , , E D U U U G U iso iso iso [] [] [] == = 1 4 1 , , n U QQ Q Q 5 xx yy xy SS 3 8 1 4 1 2 = + ( ) + + U QQ Q Q 4 xx yy xy SS 1 8 3 4 1 2 = + ( ) + - U QQ Q Q 1 xx yy xy SS 3 8 1 4 1 2 = + ( ) + + 160 3-D textile reinforcements in composite materials RIC5 7/10/99 8:04 PM Page 160 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:30:51 AM IP Address: 158.132.122.9