Chapter 2
A Novel Test Geometry for Characterization of Traction-Separation
Behavior in Composite Laminates Under Mode I Delamination
Devon C. Hartlen, John Montesano, and Duane S. Cronin
Abstract The integration of composite laminates into automotive structures can provide weight reduction and improvement
in occupant safety. However, the adoption of such materials requires characterization and efficient modeling of the damage
behaviors of composite laminates which may occur during crash events, such as delamination. Numerical modeling
techniques such as cohesive zone modeling require a traction-separation response for each mode of loading. The standard
test technique used to characterize Mode I delamination, the double cantilever beam (DCB), measures the critical energy
release rate; however, additional tests or inverse fitting techniques are required to characterize the full traction-separation
response. Additionally, compliance inherent in the DCB specimen can influence the measured energy release rate while the
large size of the specimen complicates the high deformation rate testing needed for crash analysis.
In this study, a novel Mode I test specimen adapted from a recent advancement in structural adhesive characterization is
applied to evaluate composite delamination. The hybrid Rigid Double Cantilever Beam (RDCB) test specimen presented
herein consists of rigid steel adherends co-molded to a composite plate containing a crack initiator. The use of steel adherends
eliminates compliance in the composite laminate and ensures the interface of interest is loaded consistently and uniformly
during tests, enabling measurement of the Mode I traction-separation behavior of composite delamination in a single test. As
an example, the hybrid RDCB geometry is used to characterize the Mode I delamination behavior of a unidirectional E-glass
fiber/epoxy laminate under quasi-static conditions, highlighting the ability of this specimen geometry to extract a full tractionseparation behavior from a single test.
2.1 Introduction and Background
With increasingly strict emission limits placed on automotive manufacturers, there is a push toward integrating lightweight
materials such as fiber-reinforced polymers (FRPs) into production automobiles to reduce vehicle weight and increase fuel
efficiency [1]. In addition to being lightweight, FRPs also have greater stiffness-to-weight and energy absorption properties
compared to traditional steel components [2]. However, their adoption is slowed, in part, due to a lack of maturity in modeling
the damage accumulation and failure modes of composite materials that may occur in extreme events such as impact or crash
scenarios. One modeling approach being investigated to predict the delamination behavior of FRP components is cohesive
zone modeling (CZM). However, a traction-separation law (TSL) representing the material response of the FRP is required
when using CZM, which further necessitates characterizing the delamination behavior of the FRP.
The de facto method for characterizing Mode I delamination is the double cantilever beam (DCB) test [3]. While widely
used and studied, the DCB test is only capable of directly measuring the Mode I critical energy release rate (CERR) of the
FRP. Additional tests or inverse fitting techniques are needed to extract the mechanical properties required to define the TSL
for a specific material fully. Furthermore, the compliance of the DCB specimen can affect the calculation of CERR in some
data reduction schemes or test conditions [4].
One approach to mitigate the issue of DCB specimen compliance developed by Marzi et al. [4] was to bond aluminum bars
to the top and bottom of composite DCB specimens to increase specimen rigidity. While this improves the measurement of
CERR, inverse methods are still required to extract other TSL parameters. However, a recent advancement in the characterization of adhesive behavior presents a potential alternative to the DCB test. The rigid double cantilever beam (RDCB)
specimen and analysis technique presented by Watson et al. [5] makes use of metallic adherends, which are effectively rigid
compared to the interface material being testing. This rigidity makes it possible to extract the full traction-separation response
D. C. Hartlen (*) · J. Montesano · D. S. Cronin
Department of Mechanical and Mechatronic Engineering, University of Waterloo, Waterloo, ON, Canada
e-mail: Devon.Hartlen@UWaterloo.ca; John.Montesano@UWaterloo.ca; Duane.Cronin@UWaterloo.ca
© The Society for Experimental Mechanics, Inc. 2021
R. P. Singh, V. Chalivendra (eds.), Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 6,
Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59868-6_2
5
A Novel Test Geometry for Characterization of Traction-Separation
Behavior in Composite Laminates Under Mode I Delamination
Devon C. Hartlen, John Montesano, and Duane S. Cronin
Abstract The integration of composite laminates into automotive structures can provide weight reduction and improvement
in occupant safety. However, the adoption of such materials requires characterization and efficient modeling of the damage
behaviors of composite laminates which may occur during crash events, such as delamination. Numerical modeling
techniques such as cohesive zone modeling require a traction-separation response for each mode of loading. The standard
test technique used to characterize Mode I delamination, the double cantilever beam (DCB), measures the critical energy
release rate; however, additional tests or inverse fitting techniques are required to characterize the full traction-separation
response. Additionally, compliance inherent in the DCB specimen can influence the measured energy release rate while the
large size of the specimen complicates the high deformation rate testing needed for crash analysis.
In this study, a novel Mode I test specimen adapted from a recent advancement in structural adhesive characterization is
applied to evaluate composite delamination. The hybrid Rigid Double Cantilever Beam (RDCB) test specimen presented
herein consists of rigid steel adherends co-molded to a composite plate containing a crack initiator. The use of steel adherends
eliminates compliance in the composite laminate and ensures the interface of interest is loaded consistently and uniformly
during tests, enabling measurement of the Mode I traction-separation behavior of composite delamination in a single test. As
an example, the hybrid RDCB geometry is used to characterize the Mode I delamination behavior of a unidirectional E-glass
fiber/epoxy laminate under quasi-static conditions, highlighting the ability of this specimen geometry to extract a full tractionseparation behavior from a single test.
2.1 Introduction and Background
With increasingly strict emission limits placed on automotive manufacturers, there is a push toward integrating lightweight
materials such as fiber-reinforced polymers (FRPs) into production automobiles to reduce vehicle weight and increase fuel
efficiency [1]. In addition to being lightweight, FRPs also have greater stiffness-to-weight and energy absorption properties
compared to traditional steel components [2]. However, their adoption is slowed, in part, due to a lack of maturity in modeling
the damage accumulation and failure modes of composite materials that may occur in extreme events such as impact or crash
scenarios. One modeling approach being investigated to predict the delamination behavior of FRP components is cohesive
zone modeling (CZM). However, a traction-separation law (TSL) representing the material response of the FRP is required
when using CZM, which further necessitates characterizing the delamination behavior of the FRP.
The de facto method for characterizing Mode I delamination is the double cantilever beam (DCB) test [3]. While widely
used and studied, the DCB test is only capable of directly measuring the Mode I critical energy release rate (CERR) of the
FRP. Additional tests or inverse fitting techniques are needed to extract the mechanical properties required to define the TSL
for a specific material fully. Furthermore, the compliance of the DCB specimen can affect the calculation of CERR in some
data reduction schemes or test conditions [4].
One approach to mitigate the issue of DCB specimen compliance developed by Marzi et al. [4] was to bond aluminum bars
to the top and bottom of composite DCB specimens to increase specimen rigidity. While this improves the measurement of
CERR, inverse methods are still required to extract other TSL parameters. However, a recent advancement in the characterization of adhesive behavior presents a potential alternative to the DCB test. The rigid double cantilever beam (RDCB)
specimen and analysis technique presented by Watson et al. [5] makes use of metallic adherends, which are effectively rigid
compared to the interface material being testing. This rigidity makes it possible to extract the full traction-separation response
D. C. Hartlen (*) · J. Montesano · D. S. Cronin
Department of Mechanical and Mechatronic Engineering, University of Waterloo, Waterloo, ON, Canada
e-mail: Devon.Hartlen@UWaterloo.ca; John.Montesano@UWaterloo.ca; Duane.Cronin@UWaterloo.ca
© The Society for Experimental Mechanics, Inc. 2021
R. P. Singh, V. Chalivendra (eds.), Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 6,
Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59868-6_2
5