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ENGT5152 Composite Materials

Question:

Objectives:

(1) Learn how to deal with angle lamina in structural analysis

(2) Familiarise with the steps and procedures in macromechanical analysis of laminates.

(3) Develop skills in laminate design with the help of computer programming and computational techniques.

(4) Awareness of the social, ethical and environmental impacts of using composite materials.

The Design Problem

A 2 m long cylindrical pressure vessel (Figure 1) with an inner diameter of 0.8 m is subjected to an internal gauge pressure of 2.0 MPa. The vessel operates at room temperature. High strength steel with a yield strength of 800 MPa was initially used in the design to make the vessel. The required safety factor is 2.0. It is recommended to replace steel by carbon fibre/epoxy composite laminates. The same safety factor of 2 must be achieved in the laminate design. The cost of a carbon fibre/epoxy lamina is 5 units/kg and cost of steel is 1 unit/kg.

The following are other specifications of the design:

(1) Only a type of carbon fibre/epoxy lamina is allowed. The properties of the lamina are given in Table 1.

(2) The thickness of each lamina is 0.2 mm.

(3) Only 0°, +45°, –45°, +60°, –60°, and 90° plies can be used.

Table 1: Properties of carbon fibre and epoxy lamina

 Axial Young’s modulus E1 (GPa) Transverse Young’s modulus E2 (GPa) Poisson’s Ratio n12 Shear modulus G12 (GPa) Axial tensile strength (MPa) Axial compressive Strength (MPa) Transverse Tensile strength (MPa) Transverse compressive strength (MPa) Shear strength (MPa) Density (g/cm3) 250 12 0.27 9 1800 1800 65 230 75 1.8

(1) Conduct stress analysis of the pressure vessel to determine the relationship between stress, pressure, vessel dimension and vessel wall thickness.

(2) Find applied loads in x and y directions, Nx and Ny, in N/m.

(3) Design the stacking of the lamina layers, considering orientation and number of layers.

(4) Using the Programme “Laminate” to find out global and local stresses and the safety factor (SF) for each layer.

(5) If SF is smaller than 2 in one or more layers, then increase the number of layers or change orientations (must be symmetric), and conduct the analysis again. You may need several attempts before achieving a SF larger and close to 2 in every layer.

(6) If SF is much larger than 2 in all layers, then reduce the number of layers or change orientations (must be symmetric), and conduct the analysis again. You may need several attempts before achieving a SF larger and close to 2 in every layer.

(7) If SF is larger but close to 2 in every layer, then the design is valid.

(8) Try other stacking/orientation combinations, repeat steps (3) to (6).

(9) Determine the design which requires the minimum number of layers.

(10) Use the optimum design, calculate the volume, weight and relative cost of the composite to be used.

(11) Compare the values in (10) for the composite to those for steel, and comment on weight saving, cost, health and safety issues, and recycling and environmental impact of using composites in this application.

(12) Write your report in a standard format and submit by the deadline specified on the Blackboard

Report

Your report should contain (but not limit to) the following:

1. Introduction ….. Introducing background of pressure vessels, their traditional design, material and manufacturing, and aim and objectives of this assignment.

2. Force and stress analysis to determine acting forces in N/m.

3. Procedures in macro-mechanical analysis of laminates.

4. Laminate design

(a) Your strategy in design of the laminate for the pressure vessel.

(b) Your stacking combinations, results from “Laminate” and iterations involved for each stacking.

(c) Your optimal design with explanation.

(d) Calculation of volume, weight, cost ……

(e) Design with steel as the material, calculation of volume, weight, cost ….

5. Discussion

(a) Weight saving

(b) Cost comparison

(c) Thickness and volume comparison

(d) Manufacturing route

(e) Potential health and safety issues using composite materials

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