Kahdeem Cohens completed an internship at Sikorsky Aircraft Corporation in their Materials and Process Engineering department. The internship involved analyzing composite materials and components for various types of defects through techniques like interlaminar shear strength testing, microscopy, salt fog testing, and fluorescent penetrant inspection. The document provides details on projects analyzing failures in composites, metals, and castings as well as methods for measuring bond lines, scratches and corrosion.

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Kahdeem Cohens
Princeton University, 2017
Major: Chemical and Biological Engineering
SIK Placement: M&P/MET Lab
Materials and Process Engineering
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EXEMPTION NOTICE FURNISHED IN CONFIDENCE AND SUBJECT TO EXEMPTION UNDER SUB-SECTION (B) OF USC 552”

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Index of Projects
Composites
Laminate Layup, Curing Cycle, SBS
Machining & Testing
Measurements
Keyence
Bond line thickness
Radius of curvature
Caliper
Blade thickness
Interlaminar Shear Thickness
Replica Material
Length, Width, and Depth Measurements of
Scratches/Nicks
Salt Fog Chamber
Applying Adhesive Sealant to Panels
Lightning Strike Panel Photo-
Documentation and Analysis
(Groundbreaking Material)
Fatigue/Wear
Tensile Specimen Analysis
Locating the Origin
SEM Analysis to determine the mode of
failure
Fracture Analysis
Opening Bushings (Back cutting, squeezing
with vise)
Fluorescent Penetrant Inspection (FPI)
Wear
Spalling, Pitting, Abrasions, Dents, Nicks,
etc.
Seen on planetary pinions, ring gears, sun
gears, bearings, and a TGB Output Flange
Push Horn End Horn Bearing
Seized bolt required removal without damaging
other component, disassembly required, bolt
galling
Spectrometry
Housing Analysis—Porosities, Shrinkage Sponge ,
Shrinkage Cavity, Foreign Material
PROPERTY OF SIKORSKY AIRCRAFT. SEE TITLE PAGE.

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Focus: Composite Material Marker Study
Interlaminar Shear Strength Testing
Departments: Materials and Process (M&P) and Aeromechanics
(A/EDC)
Objective: Determine whether or not various markers alter the
strength of three different pre-impregnated (pre-preg) materials,
through interactions with resin. Interlaminar shears (or short beam
shears [sbs]) were machined and tested using a Static Tester.
Example of SBS
Specimen
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The Process
1. Submission of Engineer Work Request (EWR):
 Important Aspects
 Panel Identification Numbers
 Ply Orientation, for the layup process
 Number of plies for each panel according to the prepreg’s Sikorsky Spec.
 Cure Cycle, Cross-Hatch Marking Pattern, Bagging/Layup Schematic
PROPERTY OF SIKORSKY AIRCRAFT. SEE TITLE PAGE.

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2. Execution: Layup and Bagging Schematic
 Panels were marked using a gridlines
 Panels were then laid up carefully: air bubbles avoided, alignment
ensured
 Compressed (air vacuum) according to spec.
 Bagging
 Panels held in place by rubber strips—prevents panel from growing larger
 Metal caul plates placed on top to distribute pressure evenly
 Layer of Teflon applied to contain the resin
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The Process

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3. Machining Interlaminar Shears
1. Panels prepped for saw cutting
 Blade used to cut all composites
2. Panels prepped and readied for surface grinding to determined width
 Each pass in the machine takes some off
 Coolant is used alongside a dust vacuum system
3. Panels prepped for saw cutting to requested dimensions (refer to step
1)
1. This is the general process for machining interlaminar shears and dimensions
may vary based on the requests of the engineer
The Process

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4. Interlaminar Shear Strength Testing (ksi)
 All specimens screened for thickness (see chart below)
 Groups of similar thicknesses tested—ensures a consistent sample testing
group
 “I like to work smarter not harder.” – Herbie Rivera (A/EDC Technician)
 Static Tester used for testing
 Loading nose applies force until it senses a break
 Displacement of loading nose and applied force
values visually recorded
The Process

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 Digital microscope goes up to 200x
 Uses
 High magnification shots
 Bond line thickness measurements
 Depth measurements (using replica material)
 Radius of curvature (using replica material)
Keyence—Digital Microscope

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 Chamber used to simulate intense tropical conditions
 Different surface materials tested
 Panels coated with adhesive sealant, surface is the only exposed
part of the panel
 Corrosion expected after a certain number of hours
Salt Fog Chamber
Coated panel displaying
corrosion
Panel displaying corrosion,
salt
Panel displaying corrosion,
salt

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Lightning Strike Panels
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 Material subjected to high voltage lightning strikes to determine
whether or not it could withstand them for potential use on the outer
shell of future helicopters

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 Fracture Surfaces
 Overload, Scanning Electron Microscope (SEM)
Fatigue and Wear
Lab Fracture Brass Bushing, Low Mag. Lab Fracture Brass Bushing, High Mag.
Lab fracture—used for comparison with
original fracture; manmade
Overload—fracture caused by a single
event; surpassed elastic stage
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Honeycomb structure, seen in
photos above, signify
overload mode of failure

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 Fracture Surfaces
 Possible Failure Modes
 Overload
 Fatigue
Fatigue and Wear: Tensile Specimens
Locating the Origin of the Fracture

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 FPI brings to light indications/fractures/defects that would otherwise
be overlooked
 Used under black light
 How it works:
1. Piece is swabbed with penetrant
2. Penetrant allowed to settle
3. Nondestructive material used to remove penetrant
4. If present, cracks, fractures, and/or indications become visible
Fatigue and Wear: Fracture Analysis
Fluorescent Penetrant Inspection (FPI)
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Wear: Spalling, Nicks, Dents, Pitting,
and Abrasion
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 Various parts underwent ground testing and failed
 Others accrued wear over time while out in the field
 Ring Gear, Pinion, Free Wheel Units, Droop Ring
Support Bracket, TGB Output Flange, Push Rod
Assembly Bolts
 Spalling, denting, pitting, abrasions, and nicks were
observed on these parts

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Push Rod End Rod Bearings
Seized Bolts due to Galling
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 Two push rods were received with bolts seized to the inner member as
a result of galling
 Sent without proper sealant
 Galling: form of wear caused by adhesion, here, of two metals

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 Received two defective castings for defect verification and further
analysis
 Defects range from sponge shrinkage & gas porosities to foreign
material and shrinkage cavities
 These also range in severity from 1 to 5
Spectrometry
Defective Casting
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Defective areas were
marked and
sectioned for x-rays
and tensile tests