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D M h i i C iDamage Mechanics in Composite MaterialsMaterials
Dr. Bijan MohammadiSchool of Mechanical Engineeringg g
Iran University of Science and Technology
Chapter 2Chapter 2
Damage Mechanisms in Laminated Compositesp
Various mechanisms of damage in composite l i tlaminates
(a) Matrix Cracking(c) Fiber/Matrix Debonding
(b) Delamination
(d) Fiber Fracture
Matrix Cracking Formationg
Different kinds of Damage Mechanismsff f g
• Over the course of the experimental investigation several f p gdistinct damage modes were identified including:– Matrix crack‐induced microcracking
M i k i d d d l i i– Matrix crack‐induced delamination– Angle‐ply edge delamination– Mode I edge delaminationg
Matrix crack accumulation
• Matrix crack accumulation:– Matrix cracks form within a given ply group in a direction
parallel to the fibers in that ply group. M t i ki i f tl th i iti l d d d– Matrix cracking is frequently the initial damage mode and matrix cracks may accumulate to high densities with increased loading.
Matrix crack‐induced microcrackingg
• Matrix crack‐induced microcracking: g– Plies adjacent to a ply group which has suffered matrix cracking
may form microcracks (small cracks which cluster around an existing matrix crack)existing matrix crack).
– The localized microcracks may propagate throughout the ply or remain localized depending upon the laminate configuration.
Matrix crack‐induced delamination
• Matrix crack‐induced delamination:– Delamination may form at the intersection of an existing matrix
crack and an adjacent ply. Th t d f th d l i ti t t t i ifi t– The tendency for the delamination to propagate to significant length depends upon the laminate configuration.
Interior Damageg
• Matrix crack‐induced microcracks– appeared in bands surrounding the primary matrix cracks. – The density and length of the microcracks were observed to gradually
increase with the applied load.increase with the applied load. – When the microcracks grew to significant length, the effect on the
laminate stiffness was moderate, and similar to that of matrix cracks.• Matrix crack induced delamination• Matrix crack‐induced delamination
– Initiate from existing matrix cracks – Grow simultaneously with a dense band of microcracks. – This combined damage state produced immediate and complete failure
of the laminate – limited mainly to angle‐ply laminates.
Matrix crack‐induced delamination and Microcracksi [60 / 60 ] l i tin a [602/–602]s laminate
• (a) X radiograph showing• (a) X‐radiograph showing• (b) schematic representation.
X‐radiograph images showing matrix crack‐induced delamination appearing in three different laminates pp g ff
(material T300/976)
• (a) [602/–603/60]s, (b) [452/–452]s, (c) [602/–602/90]s.( ) [ 2/ 3/ ] , ( ) [ 2/ 2] , ( ) [ 2/ 2/ ]
Effect of microcrack propagation l i t tiffon laminate stiffness response
• Response of laminate which suffers combined delamination p f ffand microcracking damage (1.0 ksi = 6.89 MPa).
Damage Scenario of [602/–602]s laminate ( t i l (T800/3900 2)(material (T800/3900‐2)
• Initial damage consisted of matrix cracks in the 60° ply group g p y g p• followed immediately by matrix crack‐induced microcracking
in the –60° ply group. • Delamination formed only after applying additional strain. • No fiber breakage.
Effect of microcrack propagation l i t tiffon laminate stiffness response
• Response of laminate which suffers combined delamination p f ffand microcracking damage (1.0 ksi = 6.89 MPa).
Damage Scenario of [452/–452]s laminate t i l (T300/976)material (T300/976)
• Initial damage consisted of matrix cracks in the 45° ply group g p y g p• followed immediately by matrix crack‐induced microcracking
in the –45° ply group • and matrix crack‐induced delamination at the interface. • No fiber breakage.
Series of X‐radiograph images obtained at increasing l d l l h i k tiload levels showing crack propagation
• [602/90/–602]s laminate (material T300/976).[ 2/ / 2] ( / )
[602/90/–602]s laminate (material T300/976) Damage S iScenario
• Initial damage consisted of matrix cracks in the 60° ply group g p y g pand microcracks in the –60° ply group
• Failed specimens suffered fiber breakage in the 90° ply group l th 60° fib di ti bi d ith t i kalong the 60° fiber direction combined with matrix crack‐induced delamination at both interfaces.
Effect of microcrack propagation l i t tiffon laminate stiffness response
• Points (a), (b), and (c) correspond to X‐radiograph images in two previous slide (1 0 ksi = 6 89 MPa)two previous slide (1.0 ksi = 6.89 MPa).
X‐radiograph images at increasing load levels, microcrackti t [60 / 60 /0] l i t ( t i l T300/976)propagation at [603/–603/0]s laminate (material T300/976),
• (a) applied stress= 196.4 MPa,(b) applied stress = 228.1 MPa, ( ) pp ,( ) pp ,(c) applied stress = 254.2 MPa
Damage Scenario of [603/–603/0]s laminate ( t i l T300/976)(material T300/976)
• Initial damage consisted of matrix cracks in the 60° ply group g p y g pand microcracks in the –60° ply group.
• Microcracks slowly propagated with increased strain. • Failed specimens suffered fiber breakage in the 0° and 60° ply
groups along the –60° fiber direction.
Near the Edge Damageg g
• Angle‐ply edge delaminationg p y g– From the intersection of a matrix crack and the laminate free edge.– Angle‐ply edge delamination was usually very small– Producing a negligible effect on the laminate stiffness – Delamination growth seemed to be highly unstable– leading directly to laminate failureleading directly to laminate failure.
• Mode I edge delamination – Typically stable, gradual growth. – Usually appeared at the laminate midplane– was not observed to lead directly to laminate failure.
Magnified view of angle‐ply edge delamination i i [30/90/ 30] l i tappearing in a [30/90/–30]s laminate
Progression of angle‐ply edge delamination appearing i [30/90/ 30] l i t ( t i l T300/976)in a [30/90/–30]s laminate (material T300/976)
• (a) applied stress = 372.7 Mpa, (b) applied stress = 376.9 MPa, ( ) pp p , ( ) pp ,(c) laminate failed with maximum applied stress = 376.9 MPa
Effect of angle‐ply edge delamination on laminate tiffstiffness response
• Points (a), (b), and (c) correspond to X‐radiograph images ( ), ( ), ( ) p g p gshown in previous slide
Progression of Mode I edge delamination [45 / 45 /90] l i t ( t i l T800/3900 2)[453/–453/90]s laminate (material T800/3900‐2)
• (a) applied stress = 142.6 MPa, (b) applied stress =155.7 MPa, ( ) pp , ( ) pp ,(c) applied stress 156.4 MPa
Effect of Mode I edge delamination on laminate tiffstiffness response
• Points (a), (b), and (c) correspond to X‐radiograph images ( ), ( ), ( ) p g p gshown in Previous slide
Progression of Mode I edge delamination appearing in [30/ 30/90 ] l i t ( t i l T300/976)a [30/–30/901/2]s laminate (material T300/976)
• (a) applied stress = 344.5 MPa, (b) applied stress = 347.3 MPa, ( ) pp , ( ) pp ,(c) applied stress = 353.5 MPa
Mode I edge delamination (material T300/976) g ( / )
• (a) [90/30/–30]s, (b) [45/–45/90]s, (c) [45/–45/0/90]s.( ) [ / / ] , ( ) [ / / ] , ( ) [ / / / ]
Stiffness response plots for laminates that failed in d d l i tiedge delamination
Stiffness response plots for laminates that failed in d d l i ti M d I d d l i tiedge delamination + Mode I edge delamination
Variation of laminate strength with i i l lincreasing layup angle
Variation of laminate strength with i i l lincreasing layup angle
Variation of laminate strength with i i l lincreasing layup angle
Variation of laminate strength with increasing thi k lthickness scale
Variation in laminate strength due to increasing thi k lthickness scale.
• Specimen failures caused by angle‐ply edge delaminationp f y g p y g
Variation of laminate strength with increasing thi k lthickness scale
Variation of laminate strength with stacking sequencef g g q