The objective of this paper is to model the synergistic bond-degradation mechanisms that may occur at the interface between a fiber-reinforced polymer (FRP) that is adhesively bonded to a substrate and subjected to elevated temperature and humidity. For this purpose, a two-dimensional cohesive-layer constitutive model with a prescribed traction-separation law is constructed from fundamental principles of continuum mechanics and thermodynamics, taking into account strain-dependent, non-Fickian hygrothermal effects as well as diffusion-induced degradation in the cohesive layer. In the interest of solution tractability, a simplified approach is employed where the rate-dependent behavior in the cohesive layer is implemented through the characterization of rate dependence of the maximum stresses and maximum strains in the cohesive layer, rather than through the use of convolution integrals in the free-energy definition. The remainder of the polymeric adhesive outside the cohesive layer is modeled as a nonlinear viscoelastic continuum with time-dependent constitutive behavior. The influence of temperature and moisture concentration on the work-of-separation and on crack growth is derived from first principles. The model is implemented in a test-bed finite element code. Results predicted by the computational model are benchmarked through comparison to experimental data from mixed-mode fracture experiments performed using a moving wedge test.

1.
Needleman
,
A.
, 1987, “
A Continuum Model for Void Nucleation by Inclusion Debonding
,”
ASME J. Appl. Mech.
0021-8936,
54
, pp.
525
531
.
2.
Needleman
,
A.
, 1990, “
An Analysis of Decohesion Along an Imperfect Interface
,”
J. Mech. Phys. Solids
0022-5096,
38
(
3
), pp.
289
324
.
3.
Tvergaard
,
V.
, and
Hutchinson
,
J. W.
, 1993, “
The Influence of Plasticity on Mixed Mode Interface Toughness
,”
J. Mech. Phys. Solids
0022-5096,
41
, pp.
1119
1135
.
4.
Tvergaard
,
V.
, and
Hutchinson
,
J. W.
, 1994, “
Effect of T-Stress on Mode I Crack Growth Resistance in a Ductile Solid
,”
Int. J. Solids Struct.
0020-7683,
31
, pp.
823
833
.
5.
De Borst
,
R.
, 2003, “
Numerical Aspects of Cohesive-Zone Models
,”
Eng. Fract. Mech.
0013-7944,
70
, pp.
1743
1757
.
6.
Knauss
,
W. G.
, and
Losi
,
G. U.
, 1993, “
Crack Propagation in a Nonlinearly Viscoelastic Solid With Relevance to Adhesive Bond Failure
,”
ASME J. Appl. Mech.
0021-8936,
60
, pp.
793
801
.
7.
Roy
,
S.
,
Lefebvre
,
D. R.
,
Dillard
,
D. A.
, and
Reddy
,
J. N.
, 1989, “
A Model for the Diffusion of Moisture in Adhesive Joints. Part III: Numerical Simulations
,”
J. Adhes.
0021-8464,
27
, pp.
41
62
.
8.
Roy
,
S.
, 1999, “
Modeling of Anomalous Diffusion in Polymer Composites: A Finite Element Approach
,”
J. Compos. Mater.
0021-9983,
33
(
14
), pp.
1318
1343
.
9.
Roy
,
S.
,
Xu
,
W.
,
Park
,
S. J.
, and
Liechti
,
K. M.
, 2000, “
Anomalous Moisture Diffusion in Viscoelastic Polymers: Modeling and Testing
,”
ASME J. Appl. Mech.
0021-8936,
67
, pp.
391
396
.
10.
Roy
,
S.
,
Xu
,
W.
,
Patel
,
S.
, and
Case
,
S.
, 2001, “
Modeling of Moisture Diffusion in the Presence of Bi-Axial Damage in Polymer Matrix Composite Laminates
,”
Int. J. Solids Struct.
0020-7683,
38
, pp.
7627
7641
.
11.
Weitsman
,
Y.
, 1987, “
Coupled Damage and Moisture Transport in Fiber-Reinforced, Polymeric Composites
,”
Int. J. Solids Struct.
0020-7683,
23
(
7
), pp.
1003
1025
.
12.
El-Sayed
,
S.
, and
Sridharan
,
S.
, 2001, “
Predicting and Tracking Interlaminar Crack Growth in Composites Using a Cohesive Layer Model
,”
Composites, Part B
1359-8368,
32
(
6
), pp.
545
553
.
13.
Gao
,
H.
, and
Ji
,
B.
, 2003, “
Modeling Fracture in Nanomaterials via a Virtual Internal Bond Method
,”
Eng. Fract. Mech.
0013-7944,
70
, pp.
1777
1791
.
14.
Shirani
,
A.
, and
Liechti
,
K. M.
, 1998, “
A Calibrated Fracture Process Zone Model for Thin Film Blistering
,”
Int. J. Fract.
0376-9429,
93
, pp.
281
314
.
15.
Kutlu
,
Z.
, and
Chang
,
F. K.
, 1995, “
Composites Panels Containing Multiple Through-the-Width Delaminations and Subjected to Compression. Part II: Experiments and Verification
,”
Compos. Struct.
0263-8223,
31
(
4
), pp.
297
315
.
16.
Knauss
,
W. G.
, and
Emri
,
I.
, 1987, “
Volume Change and the Nonlinear Thermo-Viscoelastic Constitution of Polymers
,”
Polym. Eng. Sci.
0032-3888,
27
, pp.
86
100
.
17.
Popelar
,
C. F.
, and
Liechti
,
K. M.
, 2003, “
A Distortion-Modified Free Volume Theory for Nonlinear Viscoelastic Behavior
,”
Mech. Time-Depend. Mater.
1385-2000,
7
(
2
), pp.
89
141
.
18.
Schapery
,
R. A.
, 1984, “
Correspondence Principles and a Generalized J Integral for Large Deformation and Fracture Analysis of Viscoelastic Media
,”
Int. J. Fract.
0376-9429,
25
, pp.
195
223
.
You do not currently have access to this content.