A composite material is a material which is created from two or more constituent materials. These constituent materials have different chemical & physical properties and are combined to create a material with properties unlike the individual materials. Within the finished structure, the individual elements remain separate and distinct, distinguishing composites from mixtures and solid solutions. Composites provide exceptional benefits over traditional materials such as ferrous, non- ferrous, wood or concrete. Due to its unique characterization & composition, composite material provides many advantageous in terms of physical properties and design flexibility.
Some of the key benefits of the Composite are as follows:
- Long term durability
- Low maintenance
- Rapid installation
- High strength
- High strength to weight ratio
- Light weight
- High impact strength
- Corrosion resistant
- Direction strength
- Customized surface
- Directional stability
Composite sandwich constructions are generally used in various light weight structures, because of its specific stiffness and high specific bending strength compared to solid panels. As the sandwich panels are not suited to carry localized loads, these structures should be reinforced with joining inserts to equally distribute the localized loads. Composite sandwich constructions are used in aerospace industry for building the lightweight structures because they have very high specific stiffness and strength compared to solid panels.
Composite structure panels used in aerospace products have a higher strength-to-weight ratio. But due to their weak core structure, they are not suited to withstand localized loads. Hence, inserts are used to transfer such localized loads to composite panels.
Schematic diagram showing the construction of a honeycomb core sandwich panel.
(Refer: Engineered Materials Handbook, Vol. 1, Composites, ASM International, Metals Park, OH, 1987.)
When the insert holes are machined very close to the panel edges or cutouts, it may damage the core area near the hole due to weak and minimum available core material. This may result in incorrect placement of the inserts, and the core material may get dislocated. This will ultimately impact the load-carrying capacity of the panel and may result in great damage during actual loading conditions.
Also, the minimum distance between cutouts, pockets, and panel edges should be maintained to avoid tearing composite panels. Improper placement of the cutouts/pockets on the panel surface can affect the load-carrying capacity of the panel and may result in damage during loading conditions.
In order to avoid the composite panel failure during practical loading conditions, it is always recommended to maintain the minimum distance between panel edge and insert holes, minimum distance between the cutouts/pockets and panel edges & enough spacing between insert holes.
In DFMPro, the Composite module and associated rules help designers check composite design for ease of manufacturing and better quality. On executing DFMPro checks, recommendations are highlighted in CAD graphics user interface and associated values can be seen in DFMPro task pane. The structural issues mentioned above can be addressed by checking the distance criteria for insert hole, cutouts and panel edge right at the design stage. This will help eliminate the design flaws early which will reduce rework and cost of manufacturing.
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