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MMAE 370 LAB#4: Experiment Design-Testing the Mechanical Pro

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Anurup Kankanhalli

on 3 December 2015

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Transcript of MMAE 370 LAB#4: Experiment Design-Testing the Mechanical Pro

Experiment Design - Testing the Mechanical Properties of Carbon fiber as a Function of Fiber Orientation

Specific Stiffness:
Ratio of elastic modulus of material to its mass density
Characteristic of low-weight, high strength materials that find applications in the aerospace and automotive industry.
From the results obtained in the lab, there seems to be a strong correlation in the relationship between fiber direction, manufacturing methods and stiffness.
Composite material: Combination of two or more chemically distinct and insoluble phases with recognizable interface such that its properties and structural performance are superior to those of the constituents acting independently
Fiber composites: consists of fibers in polymer matrix
Has high specific strength (strength to weight ratio) and specific stiffness (stiffness to weight ratio)
Highly anisotropic (direction dependent)
Highest stiffness and strength when fibers align in direction of tension force
Challenges of creating complex structures out of composites
Controlling environment
Following strict standards
ie: eliminating voids

Proposed lab experiment to test the anisotropic behavior of carbon fiber when layered in different orientations in a bending test.
Additionally analyze the effect of certain manufacturing methods on the stiffness of the material
It is composed of facings, a firm core and adhesive.
3 point Bending Test:
Loading at 3 points, used to analyze Elastic modulus of the sandwich.
Best way to measure the properties of the sandwich since one facing is in tension, the other in compression and shearing in core.
Testing for properties
3 point or 4 point bending test
common testing method for brittle materials
Load is applied vertically to either:
One point= three-point bending (a)
Two points= four-point bending (b)
Upper surface= compressive stress
Lower surface = tensile stress
Stress calculated using simple bean equation
Stress at fracture of bending = modulus of rupture
four-point test gives a lower modulus of rupture than the three-point
Carbon fiber aluminum honeycomb sandwich
Reason for Experiment
Carbon fiber electric car for lightness and equivalent strength of steel
This needs to be proved for SAE Formula competition
Orientation of fibers is looked at to reduce weight even further
Stronger panels are used in areas of the car that actually need impact protection, helping minimize weight and optimize on track performance
Sandwich structure
Composite made of stiff skins with a low density core
Metal matrix materials in core: aluminum, aluminum-lithium alloy (lighter than aluminum), magnesium, copper, titanium, and super alloys
Fiber skin materials: graphite, boron, alumina, silicon carbide, molybdenum, and tungsten

Many materials are used in the layup process (next slide)
CYCOM 5320-1
HEXCEL 5052 Aluminum core
Carbon fiber stored in freezer for longer shelf life
Materials needed to be cut prior to layup
Template used for the bending test
Oversized template was also used so edges could be cut off
ASTM C393 changed to fit Formula SAE competition rules

The layup process
Vacuum check
Don’t lose more than 2in Hg of vacuum in 5 minutes
Ramped 5 deg F per minute to 250, hold for 3 hours
Raised then to 350, held for 2 hours for post-cure
Cutting with abrasive tile cutting saw

3 point bending test is performed (ASTM C393 standards followed)
Pressure pads added to prevent stress concentrations
Shore hardness done on pressure pads , got 60
Span was calculated to be equivalent to standard for our oversized sample
Only two valid failure modes, shear of core and delamination
Measured force vs displacement using Instron 5500 R

3 point bending test in action
Table of Validity of bending tests

Calculations of specific stiffness

Elastic modulus calculations and results plot
Fiber orientation plot

Differences in procedure plot

Error analysis
Loss of vac
Increase of mass, possibly due to moisture content
Failure of facing
Differences in highest point used to calculate stiffness
Uncertainty of failure mode
Most likely failed due to shear of the core because when the double adhesive sample was tested, the strength was the same

There is a definite relation between fiber orientation and stiffness.
In general, stiffness is greatest when oriented in direction of fibers
Manufacturing method also affected stiffness
Not very much difference in vac vs no vac
Core orientation increased stiffness
Double film adhesive also increased stiffness
It is important to follow procedure carefully because it can greatly affect the end product

SAE – orient the carbon fiber to maximize strength and stiffness in certain directions to save weight
Used in the aerospace industry for light weight and high stiffness

[1] NDT Resource Center, "Composite Structures," [Online]. Available: http://www.ndt-ed.org/. [Accessed 11 November 2013].
[2] NDT Resource Center, "Composite Structures (Continued)," [Online]. Available: http://www.ndt-ed.org/. [Accessed 11 November 2013].
[3] B. Lii, "Design and Manufacture of a Composite Monocoque Chassis," University of Queensland, Queensland, 2009.
[4] J. E. Little, X. W. Yuan and J. M. I, "Voids Characterization in Carbon Fibre/Epoxy Composite Laminates," University of Auckland, Auckland.
[5] HEXCEL Composites, "Hexweb Honeycomb Attributes and Properties," 1999. [Online]. Available: hexcel.com. [Accessed 3 November 2013].
[6] "Hexweb Honeycomb Sandwich Design Technology," December 2000. [Online]. Available: hexcel.com. [Accessed 3 November 2013].
[7] Cytec Engineered Materials, "CYCOM 5320-1 Epoxy Resin System Technical Data Sheet," 19 March 2012. [Online]. Available: www.cytec.com. [Accessed 3 November 2013].
[8] SAE International, "2014 Formula SAE Rules," 2014.
[9] ASTM International, "Standard Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure," ASTM International, West Conshohocken, PA, 2012.
[10] D. Richardson, "The Fundamental Principles of Composite Material Stiffness Predictions," [Online]. Available: http://www.swcompositesgateway.co.uk/. [Accessed 19 November 2013].

Error Analysis
Anurup Kankanhalli, David Foehring, Inho Park, Kyeonggon Choi and Nicholas Peake
Illinois Institute of Technology
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