Composites are materials made from two or more constituent materials with different physical or chemical properties. A composite part must withstand various loadings, so the designer chooses the reinforcement, matrix, and curing process based on functional requirements. Important considerations for composite part design include fiber orientation to optimize mechanical behavior, midplane symmetry to prevent warping, and stress concentrations from holes. Joints require methods like bolting, bonding, inserts or scarf joints to transfer loads while preventing failure.
Composites are materials made from two or more constituent materials with different physical or chemical properties. A composite part must withstand various loadings, so the designer chooses the reinforcement, matrix, and curing process based on functional requirements. Important considerations for composite part design include fiber orientation to optimize mechanical behavior, midplane symmetry to prevent warping, and stress concentrations from holes. Joints require methods like bolting, bonding, inserts or scarf joints to transfer loads while preventing failure.
Composites are materials made from two or more constituent materials with different physical or chemical properties. A composite part must withstand various loadings, so the designer chooses the reinforcement, matrix, and curing process based on functional requirements. Important considerations for composite part design include fiber orientation to optimize mechanical behavior, midplane symmetry to prevent warping, and stress concentrations from holes. Joints require methods like bolting, bonding, inserts or scarf joints to transfer loads while preventing failure.
Composites are materials made from two or more constituent materials with different physical or chemical properties. A composite part must withstand various loadings, so the designer chooses the reinforcement, matrix, and curing process based on functional requirements. Important considerations for composite part design include fiber orientation to optimize mechanical behavior, midplane symmetry to prevent warping, and stress concentrations from holes. Joints require methods like bolting, bonding, inserts or scarf joints to transfer loads while preventing failure.
Composites Presented By: - William Daryl Licup - Karl Gabriel Patula - Miggie Lemence What Are Composites? What Are Composites? A composite material is a combination of two materials with different physical and chemical properties. When they are combined they create a material which is specialized to do a certain job, for instance to become stronger, lighter or resistant to electricity. They can also improve strength and stiffness. DESIGN OF A COMPOSITE PIECE CONCEPTION AND DESIGN As every mechanical part, a composite part has to withstand loadings. In addition, the conception process has to extend over a range much larger than for a component made of “pre-established” material. In fact;
- For isotropic materials, the classical process of conception consists of selection of an
existing material and then design of the piece. - For a component made of composites, the designer “creates” the material based on the functional requirements. The designer chooses the reinforcement, the matrix, and the process for curing DESIGN OF A COMPOSITE PARTS The following characteristic properties always have to be kept in mind by the designer:
- Fiber orientation enables the optimization of the mechanical
behavior along a specific direction. - The material is elastic up to rupture. It cannot yield by local plastic deformation as can classical metallic materials. - Fatigue resistance is excellent. A Very Good Fatigue Resistance The specific fatigue resistance is expressed by the ratio , with r being the specific mass.
Comparison of Fatigue Behavior Between Composite and Aluminum
Guidelines and Values for Predesign
This shows a comparison between different materials, which can help
in the choice of composite in the pre design phase. Guidelines for Values for Predesign The orders of magnitude of safety factors are as follows: Importance of Ply Orientation
One of the fundamental advantages of laminates is their
ability to adapt and control the orientation of fibers so that the material can best resist loadings. It is therefore important to know how the plies contribute to the laminate resistance, taking into account their relative orientation with respect to the loading direction. Middle Plane By definition the middle plane is the one that separates two half- thicknesses of the laminate. What is midplane symmetry It is the symmetry to when the plies above the midplane are a mirror image of those below the midplane. For the construction of laminated pieces, the successive impregnated plies are stacked at ambient temperature, then they are placed within an autoclave for curing. At high temperature, the extension of the whole laminate takes place without warping. However, during cooling, the plies have a tendency to contract differently depending on their orientations. From this, thermal residual stresses occur. Particularities of the Behavior of Laminates
When one unidirectional sheet
does not cover the whole surface required to constitute a ply, it is necessary to take precautions when cutting the different pieces of the sheet. The unidirectional sheets do not fit well into sharp corners in the fiber direction. JOINING AND ASSEMBLY
A second fundamental aspect of
the design of a composite piece consists of the design for the attachment of the composite to the rest of the structure. In all mechanical components, the introduction of holes gives stress concentration factors. The equilibrium diagrams shown in this figure demonstrate the increase in stress concentration in the case of a laminate. During the hole cutting process, or the misalignment of fibers if the hole is made before polymerization, the figure illustrates the correlation between the weakened zones consecutive to rupture of fibers and the “overstressed” zones. Principal Modes of Failure in Bolted Joints for Composite Materials Bolted Joints Evaluation of the admissible stresses in connecting a joint between metal and laminate material. The principle of calculation consists of magnifying the stresses that are given by elementary considerations, by means of the empirical coefficients of magnification. The tightening of the bolt is therefore indispensable. However, the laminated facings being fragile cannot admit high contact pressures that are localized under the bolt head and under the nut. This leads to the insertion of metallic washers. BONDING Remember briefly that this assembly technique consists of the adhesion by molecular attraction between two parties to be bonded and an adhesive that must be able to transfer the loads. One can cite the principal advantages of this mode of joining:
● Distribution of stresses over an important surface
● Possibility to optimize the geometry and dimension of bonding ● Lightweight of assembly ● Insulation and sealing properties of adhesive Adhesives Used: Things to consider during bonding: Fracture of Bonded Assembly Geometry of Bonded Joints Design for the Transmission of Couples Scarf Joint
Parallel Joint Guidelines in Adhesive Joint Designs Stresses in Adhesive Maximum Shear Stress We may be incorporated in different types of layers: Bonded Joint in Cylindrical Geometry In a laminate, orientation of the plies that are in contact with the joint influences strongly the failure by fiber–resin decohesion.
A tensile load in plies
that are in contact with the adhesive requires that fiber orientation in these plies must be along the direction of the load EXAMPLES OF BONDING Laminates
Sandwiches Different Sandwich Facing Designs INSERTS INSERTS ● It seems necessary to include in composite parts reinforcement pieces, or “inserts,” which may be used to attach to the surrounding structure. The inserts decrease the transmitted stresses to admissible values for the composite part
