FRP Composites: Overview, Characterization, Analysis ... Shortcourse-10-11Jul2014... · A Report on...
Transcript of FRP Composites: Overview, Characterization, Analysis ... Shortcourse-10-11Jul2014... · A Report on...
A Report on
Short Course “FRP 2014”
FRP Composites: Overview, Characterization,
Analysis, Design and Applications
10th & 11th July 2014
at IIT Hyderabad
Hosted by
Department of Mechanical and Aerospace Engineering,
&
Department of Civil Engineering,
Indian Institute of Technology Hyderabad
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Table of Contents
INTRODUCTION ................................................................................................................................. 2
SUMMERY OF DAY 1 ........................................................................................................................ 3
SUMMERY OF DAY 2 ........................................................................................................................ 4
DETAILS OF FRP COURSE .............................................................................................................. 5
Dr. Suriya Prakash‟s talk on „Overview of composites: Mechanical properties and applications‟ .... 5
Dr. Ramji‟s talk on „Manufacturing processes and compression behaviour of FRP composites‟ ...... 6
Dr. CM Majunatha‟s talk on „Mechanical testing of composites‟ ...................................................... 7
Mr.Kashafudoja‟s talk on „Experimental characterisation of FRPs and FEA modelling‟ .................. 8
Prof. P. Alagusundaramoorthy‟s talk on „FRP research at IIT Madras‟ ............................................. 9
Mr. Srinivas Aluri‟s talk on „Applications of FRP in bridges‟ ......................................................... 10
Dr. Viswanath‟s talk on „Mechanics and damage of FRP composites‟ ............................................ 11
Director‟s address ............................................................................................................................. 12
FEEDBACKS FROM PARTICIPANTS .......................................................................................... 13
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INTRODUCTION
Fiber-reinforced polymer (FRP) composite are now being extensively used as primary and secondary
load bearing members in many industries like aerospace, automobile, civil infrastructure, wind
energy, marine and sports. The feature of custom tailored properties and heterogeneous nature offered
by composites call for special attention to their characterization. Testing of heterogeneous and
anisotropic FRP materials poses several challenges like numerous parameter identification,
development of specific test methodology and fixtures etc. As a whole, the knowledge of fabrication
methods, accurate machining and testing methodology is essential for researchers and practicing
engineers from design and manufacturing perspective.
Keeping in mind this purpose, IIT Hyderabad organized a short course on “FRP composites:
Overview, characterization, analysis, design and applications” on JULY 10th
-11th
, 2014 focusing on
following aspects:
1. Introduction to Composites
2. Manufacturing Processes
3. Basic Mechanics
4. Material Characterization
5. Whole-field Strain Analysis using Digital Image correlation (DIC) technique
6. Mechanics of Composite Repair
7. Fatigue life assessment
8. Applications and Case Studies
Invitations were sent to many engineering colleges and industries across India. Around 75 participants
attended this short course. Number of students also showed interest to attend the course along with
faculty members and industrialists. Speakers with expertise on FRP composites were invited from
academic and research organizations as well as from industries so that participant could get the
flavour of research and applications of FRP composites across the domain.
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SUMMERY OF DAY 1
The day 1 began with the welcome speech by Prof. V. Eswaran, Head of Mechanical and Aerospace
Engineering. After that, there was a brief introduction about TEQIP program by Prof. N. Venkata
Reddy, Dean (R&D), TEQIP coordinator, IITH. He summarised various programs organised under
TEQIP program at IIT, Hyderabad. Thereafter, Dr. Suriya Prakash presented the overview of FRP
composites. He discussed about the applications of composites in modern day life. Following his talk,
Dr. M. Ramji gave the overview about various manufacturing processes used for preparing the
composite laminates and structures. Various materials used in composite structures were introduced in
this presentation. Later, Dr. C. M. Manjunatha discussed about the mechanical characterisation of
composites. In his talk, he presented various design philosophies used in design of composite
structures. Various tests mentioned in standards were introduced along with interpretation of results.
In the afternoon, Mr. Kashafudoja presented his work related to characterisation of composite
materials. He introduced participants with various ASTM standards used for testing. He presented
about Digital Image Correlation (DIC) and concluded his talk with results obtained for open cutout
CFRP panel. In the following session, he focussed on Finite Element Modelling of composites. He
gave a demo in ANSYS software using Graphical User Interface (GUI) as well as APDL codes. Then
all the participants visited the IITH central workshop to view various manufacturing and testing
facilities related to composites. This visit concluded the sessions of day 1.
Prof. V. Eswaran,
Head of Mechanical and
Aerospace Engineering
Prof. N. V. Reddy,
Dean (R&D) and TEQIP
coordinator
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SUMMERY OF DAY 2
The second day program began with the talk by Dr. C. M. Manjunatha about the fatigue testing of
composites. He talked about various damage mechanisms in composites under fatigue loading.
Thereafter, he outlined the methods for fatigue testing, data collecting and post-processing of data.
Followed by him, Dr. M Ramji talked about compressive behaviour of composites. His talk focused
on the importance on behaviour of composites under compressive loading. He then presented various
compressive failure modes. Prof. Alagusundaramoorthy P. (Professor, IIT Madras) talked about FRP
research at IIT, Madras. Various applications of FRP‟s were discussed illustrated through various
projects done at IIT Madras. Thereafter, Mr. Srinivas Aluri (Hara industries) talked about the
applications of FRP‟s in bridge structures. Various applications in bridges were discussed along with
the dynamic response characteristics of FRP bridges. In the afternoon session, Sika India listed their
various products along with their advantages. Thereafter, the presentation by ATOS about Non
Destructive Testing was followed. The Infrared testing method was introduced. Dr. Viswanath
Chinthapentha presented about mechanics and damage in FRP composites focusing analytical aspects.
Finally, an interactive feedback session was conducted by Dr. M Ramji. After this session, all the
participants were awarded with the certificates for attending the course. This concluded the day 2 as
well as the overall FRP course.
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DETAILS OF FRP COURSE
Dr. Suriya Prakash‟s talk on „Overview of composites: Mechanical properties
and applications‟
(10:00 AM to 11:00 AM, 10th July)
Dr. Suriya Prakash from IIT Hyderabad talked mainly about introducing the basics of composites.
Starting with the definition of Fiber Reinforced Polymers (FRPs), he listed various mechanical
properties that are needed for the analysis of composites. Thereafter, he presented on classifications of
composites. There are many types of composites eg. Particle reinforced, fiber reinforced, structural
laminates etc. Then the sizes of various types of reinforcements were compared. He briefly discussed
about the applications of FRPs in various fields along with advantages and challenges in their
practical application. Each constituent of FRP performs a different role. The matrix supports the fibes
and keeps them together while fibers are the main load taking members. He then talked about
properties of Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP).
Finally, the temperature effect on mechanical behavior of FRPs was discussed along with the effect of
fatigue loads.
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Dr. Ramji‟s talk on „Manufacturing processes and compression behaviour of
FRP composites‟
(11:15 AM to 12:15 AM, 10th
July & 10:00 AM to 11:00 AM, 11th
July)
Dr. Ramji from Indian Institute of Technology, Hyderabad (IITH) discussed about the manufacturing
methods of composites. He talked about the mechanical properties of fibers and matrix materials.
Various manufacturing processes used for manufacturing glass fibers and carbon fibers were
discussed. The properties of continuous fiber, chopped fiber composites, pultruded sections were
compared. There are various methods for manufacturing composites like resin transfer process,
vacuum infusion process, hand layup process etc. Various factors that affect the properties of
composites were discussed.
On the second day, He discussed about behaviour of composite laminates under compressive loading.
At start he briefly discussed about various applications of composites in modern day world. Then he
told about the importance of compressive strength and damage analysis in composites. In
compression, local micro-buckling of fibers are the main failure unlike fiber breakage in tension.
There are various mechanisms by which FRPs fail in compressive loading. They are fiber
microbuckling, kinking, fiber crushing, splitting, buckle delamination.
Talk then followed the experimental procedure for compressive testing of composites. Special types
of fixtures were introduced to carry out the testing. SACMA and UCSB fixtures were used to carry
out tests. Then the results obtained from experiment and Digital Image Correlation (DIC) technique
were compared with the results obtained from Finite Element Analysis. Then the concept of
Progressive Failure Analysis (PFA) was introduced to understand the damage mechanics in
composites. Various cases of damage propagation were presented eg. Single hole in panel, two
interacting holes in panel etc. The talk was concluded with question and answers session.
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Dr. CM Majunatha‟s talk on „Mechanical testing of composites‟
(12:15 AM to 01:15 PM, 10th
July & 09:30 AM to 10:00 AM, 11th
July)
Dr. CM Manjunatha is currently working as a Senior Principal Scientist and Group Head, Fatigue and
Structural Integrity Group, CSIR-NAL. He talked about mechanical characterization of composites.
He started with the discussion on three different design approaches: safe-life design, fail-safe design
and damage tolerant design. He emphasized on the building block approach for design of structures
which starts with coupon testing and stretches up to component testing. In aerospace industry, FRP
composites widely replace the conventional metallic alloys. There is need of testing of these
composites and characterize the same. ASTM has established many standards to conduct various tests
for composites. It includes tension, compression, shear, flexure, delamination, interlaminar shear, etc.
tests. ASTM along with many other organizations has designed various fixtures to conduct all these
tests. It is also required to get the behaviour of notch effect on the structures. The wing and fuselage
features come next to coupon testing. Also repaired composite panels are also tested at CSIR-NAL. It
is very critical to get the bearing strength of CFC (carbon fiber composite) joints. The next is
component level testing which includes wing-root fitting box test, wing test, fuselage test, etc. At the
end it comes to full scale fatigue testing of aircraft.
In spite of good design, structures often fail during service due to fatigue loading. Due to uncertainty
of failure of composites, the complete potential of FRPs is not used. The main fatigue damage
includes matrix cracking, fiber break and debonding, delaminations. It is very essential to design the
structures based on fatigue criterions and also to predict service life. Fatigue life prediction under
spectrum loads is very complex. Firstly it requires the cycle count data produced through rainflow
technique and also S-N curves. Then all data is transformed into one plot called Constant Life
Diagram (CLD) curve. It is used with various damage accumulation models to predict the life of the
structures.
The recent trend is to add nano size fillers in composites to improve the properties of FRPs. It is
called nanocomposites. Nano particle reinforced epoxy exhibit higher fatigue life over that of neat
epoxy. Same is observed in GFRP. So advanced nanocomposites appear to be potential futuristic
structural materials. There are very many interesting avenues for research in the areas of fracture
mechanics and fatigue.
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Mr.Kashafudoja‟s talk on „Experimental characterisation of FRPs and FEA
modelling‟
(02:20 PM to 04:00 PM, 10th
July)
Mr. Mohammad Kashafudoja talked about the experimental characterisation of FRP‟s. He started with
applications of FRP‟s in various fields and the importance of characterisation. He talked about various
ASTM standards that are used for characterisation of FRPs. Various tests used for finding out
mechanical properties of CFRP panel were discussed. He explained the experimental procedure
followed during testing of CFRP panels. Then he discussed about the use of Digital Image Correlation
(DIC) technique in characterisation of CFRP. Then he compared the results obtained from MTS
machine with DIC results. Then he talked about repair of composites which is widely used in
aerospace industries. Single side and double side patch repair results were shown. He concluded his
talk by discussing about the progressive failure analysis.
The next session conducted by him focussed on Finite Element Modelling and Analysis of FRPs. He
demonstrated the step by step procedure to perform FEA in ANSYS software. He discussed about
both unidirectional and multidirectional composites. He demonstrated the procedure using the
graphical user interface (GUI) as well as APDL codes. Various commands used in APDL code were
discussed. This demo session was then concluded by discussing about loading process.
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Prof. P. Alagusundaramoorthy‟s talk on „FRP research at IIT Madras‟
(11:15 AM to 12:15 PM, 11th
July)
Prof. Alagusundaramoorthy from IIT Madras discussed about the research towards FRP applications
done at structural engineering lab at IIT Madras. FRP deck panels have been tested at the lab. They
have inspected and evaluated bridge deck partially reinforced with GFRP rebars. Also the research
has been done on material selection and fabrication of FRP composite bridge deck panels. They have
used contact moulding hand lay-up process and also pultrusion for bridge deck panels. They studied
the fatigue of prototype GFRP composite bridge deck panels under enhanced fatigue loading. His
research group has done flexure tests on beams bonded with CFRP sheets and fabric. They have also
done experiments on shear strength of beams wrapped with CFRP fabric. They have facility to test the
columns having height upto 5 meters. The testing of segmentally erected composite girders has also
been done. Experiments on Seismic retrofit of column in beam-column joint using glass fiber fabric
are also carried out at the lab. The strength of stiffened composite plates with cutout under a
combination of axial and out of plane load is found experimentally. Research is going on strength of
steel and glass fiber reinforced composite plates with square opening under axial and out of plane
load. They have found the behaviour of GFRP retrofitted masonry assemblage under axial
compression and shear. They have established a novel setup for testing of ship deck stiffened panels
under axial and lateral loads.
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Mr. Srinivas Aluri‟s talk on „Applications of FRP in bridges‟
(12:15 PM to 01:15 PM, 11th
July)
Mr. Srinivas Aluri from Hara Industries presented uses of FRP in bridges which includes retrofitting
of existing bridges, rebars with concrete and bridge decks/stringers. First generations of FRP bridge
deck was made of E-glass fabrics and Vinyl Ester resin. But it is very costly. Currently Prodeck 4 is
widely used bridge deck fabricated by pultrusion method. It is the third generation of FRP bridge
decks and its cost is reduced more than an half than its predecessor. Adhesive plays a major role in
transferring the load from one deck to another. Also spring clips are used to connect FRP deck
modules to girders. Its performance is evaluated using various static and dynamic testing. It is
required to check actual performance against design assumptions especially for new technologies such
as FRP. Through testing the parameters such as transverse load distribution factors, damping ratios,
natural frequencies, dynamic load allowance factor, vibration serviceability, etc. are determined. The
vibration of bridges due to moving traffic has potential problems like dynamic amplification of
stresses and vibration serviceability. The first one is accounted in design as DLA (impact factor)
while the second is not accounted in design. Dynamic Load Allowance (DLA) Factor is determined
by allowing a loaded truck to pass at 2 mph and at highway speeds. Ontario Highway Bridge Design
Code (OHBDC) chart provides an indication whether traffic-induced bridge vibrations are
perceptible. Damping usually not measured for steel-concrete & concrete bridges since inherent
damping of these bridges is sufficiently high enough to dissipate traffic induced vibrations. But
composite being lighter in weight has very poor damping properties. So Lack of inherent damping in
these bridges is the primary reason for high amplitudes of vibration. Research is currently underway
to improve damping in FRP decks using pour-in-place foams and lightweight granular materials.
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Dr. Viswanath‟s talk on „Mechanics and damage of FRP composites‟
(02:30 PM to 03:00 PM, 11th
July)
Dr. Viswanath from IIT Hyderabad discussed about the basics of stress and strain. The constitutive
law relates the stress and strain through elasticity tensor. More the internal symmetries, the simpler
the structure of the elasticity tensor. Voigt notation is very handy to describe the constitutive law. It
transfers the stress/strain tensor into a vector form. The composite panels is nothing but a stack of
laminates having different fiber orientation. The classical laminate theory (CLT) makes it possible to
relate external loads (in-plane forces and moments) to the composite plate deformations. The ABBD
matrix is a result of this theory. Going further, it is required to establish model for damage mechanics.
Right now there are many damage models are available for composites. But no model is generic and
accurate. Composites have a huge hidden potential but it cannot be used until the damage in
composites can be predicted accurately. The damage mechanics in composites becomes complex due
to multiple failure modes. There are various failure theories like Tsai-Wu, Tsai-Hill, Hashin, Puck‟s,
etc. The Tsai-Wu quadratic interaction or tensor polynomial failure criterion (Tsai and Wu, 1971)
accounts for the interactive effects of a multi-axial stress state. s. The only region which it does not
work very well is for fiber compression failure, which is actually a geometrically driven failure and
not a true material property. For that type of failure, one of the “micro-buckling” types of criteria
seems to be more accurate.
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Director‟s address
(02:15 PM to 02:30 PM, 11th
July)
Prof. U. B. Desai welcomed all the participants again on behalf of IIT-Hyderabad. He discussed about
active involvement of IIT Hyderabad in conducting different research and application oriented
programmes through TEQIP. There should be an interactive collaboration between educational
institute, research organizations and industries so that students and faculties can contribute to the
research, the major need of developing India and also this research should lead to some real and
feasible application so that society can also be benefited. He also talked about the current research
areas IIT Hyderabad working on. He appreciated the idea of organizers of conducting the course of
FRP composites which is nowadays widely used in aerospace along with other areas like marine,
automobile, etc. He requested all the participants to have a continuing interaction with IITH Faculty
and amongst themselves. He congratulated and encouraged them to participate in such activities.
Finally, he thanked Dr. Ramji and Dr. Suriya for organizing this course.
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FEEDBACKS FROM PARTICIPANTS
The issue on environmental damages should be discussed
One session on secondary manufacturing processes such as cutting, machining, polishing, etc.
could be added.
Proper illumination level should be maintained in the lecture hall.
It could be good if the students got more time to interact with the experts to clarify their
queries.
The course should be stretched up to five days to include more topics and discussion.
The transportation facility was very good.
Many participants got the ideas and direction to begin and carry out their research further.
The characterization of composite should be discussed further in detail.
Group Photo in the Lecture Hall-3
Group Photo after visit to Workshop at IITH