48 3-D textile reinforcements in composite materials Compression after Impact 6,7 [J/mm] 07 Customer Requirement 0,6 V 0.5 0.65 0,4 0.55 0.3 0,5 0.36 0,35 0.2 0.1 十 Tape Laminate Tape Laminate Tape Laminate 2-D woven 3-D woven Thermoset Interleaved Thermoplast Thermoset Thermoset 2.4 Damage tolerance of different composite materials. WV St:6Z 210e In Fig.2.4,the damage tolerances of various composite materials,char- acterized by the compression after impact test,are compared.In this test, 网 composite plates are impacted and afterwards compression tested accord- ing to exactly defined specifications.The remaining strength and breaking elongation represents a value for the damage tolerance evaluation and the design of impact-susceptible structures. It is shown that performance after impact can be improved significantly by the 3-D fibre reinforcement.With a fibre share of below 5%,the design goal of 0.5%after impact that is required in aerospace can be reached even with brittle resin systems.The parameters that influence performance are type,thickness and distance of z-fibres as well as the reinforcing geometry.Figure 2.5 illustrates the reason for higher impregnation speed.Compared with 2-D composites,the z-fibres lead to a significant improvement in bonding of the single layers,as demonstrated by the peel strength. The structural integrity is of major importance,especially for automotive applications.After a crash,the structures have to maintain a minimum mechanical performance.Complete debonding of component parts has to be avoided.These criteria can be realized easily by metals owing to their plastic deformation characteristics.The more or less brittle crush behaviour of conventional,especially carbon fibre reinforced composites is much more critical in this respect. This performance can also be improved by a 3-D fibre reinforcement
In Fig. 2.4, the damage tolerances of various composite materials, characterized by the compression after impact test, are compared. In this test, composite plates are impacted and afterwards compression tested according to exactly defined specifications. The remaining strength and breaking elongation represents a value for the damage tolerance evaluation and the design of impact-susceptible structures. It is shown that performance after impact can be improved significantly by the 3-D fibre reinforcement. With a fibre share of below 5%, the design goal of 0.5% after impact that is required in aerospace can be reached even with brittle resin systems. The parameters that influence performance are type, thickness and distance of z-fibres as well as the reinforcing geometry. Figure 2.5 illustrates the reason for higher impregnation speed. Compared with 2-D composites, the z-fibres lead to a significant improvement in bonding of the single layers, as demonstrated by the peel strength. The structural integrity is of major importance, especially for automotive applications. After a crash, the structures have to maintain a minimum mechanical performance. Complete debonding of component parts has to be avoided. These criteria can be realized easily by metals owing to their plastic deformation characteristics. The more or less brittle crush behaviour of conventional, especially carbon fibre reinforced composites is much more critical in this respect. This performance can also be improved by a 3-D fibre reinforcement. 48 3-D textile reinforcements in composite materials 2.4 Damage tolerance of different composite materials. RIC2 7/10/99 7:25 PM Page 48 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
3-D textile reinforced composites for the transportation industry 49 800 700 3-d 600 500 三 400 300 2-d 200 Thermoplast 100 Toughened Thermoset Thermoset 10 15 20 25 Notch Length (mm) 2.5 Notch growth in 2-D and 3-D reinforced composites. WV St:6 202 Figure 2.6 shows double T-shaped beams,typical structural components in automotive and aerospace design,after longitudinal and transversal crash tests.The preforms for the composite structures are integrally 3-D braided by a new'n-step'braiding process in an optimum configuration according to the loads.The integral fibre reinforcement guarantees high structural 具 integrity with locally restricted damage area and high after-crash perfor- mance.An additional feature is the high mass-specific energy absorption owing to the complex,exactly controllable failure modes in the 3-D fibre structure. More complex preforms for composites with high structural integrity which cannot be made by one textile technology can be realized by stitch- ing several basic preforms together.A stiffened panel is discussed in Chapter 5 as an example.It has been made by stitching the warp-knitted skin to a 3-D braided profile. 2.3 Manufacturing textile structural composites The diverse textile processes,such as advanced weaving,braiding,knitting or stitching,allow the production of more or less complex fibre preforms. While weavings and warp knittings are predestined for flat panels,braid- ings allow the manufacture of profiles.The most complex preforms can be realized where warp-knitting is used.Tables 2.1 and 2.2 summarize the most important features of textile process and composites as well as the
Figure 2.6 shows double T-shaped beams, typical structural components in automotive and aerospace design, after longitudinal and transversal crash tests. The preforms for the composite structures are integrally 3-D braided by a new ‘n-step’ braiding process in an optimum configuration according to the loads. The integral fibre reinforcement guarantees high structural integrity with locally restricted damage area and high after-crash performance. An additional feature is the high mass-specific energy absorption owing to the complex, exactly controllable failure modes in the 3-D fibre structure. More complex preforms for composites with high structural integrity which cannot be made by one textile technology can be realized by stitching several basic preforms together. A stiffened panel is discussed in Chapter 5 as an example. It has been made by stitching the warp-knitted skin to a 3-D braided profile. 2.3 Manufacturing textile structural composites The diverse textile processes, such as advanced weaving, braiding, knitting or stitching, allow the production of more or less complex fibre preforms. While weavings and warp knittings are predestined for flat panels, braidings allow the manufacture of profiles. The most complex preforms can be realized where warp-knitting is used. Tables 2.1 and 2.2 summarize the most important features of textile process and composites as well as the 3-D textile reinforced composites for the transportation industry 49 2.5 Notch growth in 2-D and 3-D reinforced composites. RIC2 7/10/99 7:25 PM Page 49 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
50 3-D textile reinforcements in composite materials 100 WVst:6Z:ZI I 1OZ ZZ Anutr 'Aupines 80 6'ZZI'ZEI'8SI :dl 60 40 20 0 10 20 30 40 50 60 70 Displacement [mm] 2.6 Structural integrity of 3-D braided profiles after crash
50 3-D textile reinforcements in composite materials 2.6 Structural integrity of 3-D braided profiles after crash. RIC2 7/10/99 7:25 PM Page 50 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9