16 июля, 2015 
Malyar In this study, a comprehensive program to evaluate the durability, shear strength, and fracture toughness of FRP-wood bonded interfaces was presented. The potential in-service delamination of bonded interfaces was evaluated by a 3-cycle test involving repeated wetting and drying [4]. Also, wet and dry interface strengths were evaluated through block-shear tests [4]. The fracture toughness of the interface was measured by an innovative fracture mechanics test [8]. Several key durability parameters of bonded interfaces were investigated, including use of a coupling agent (primer), open/closed assembly time, and clamping pressure; further the durability of bonded interfaces was evaluated by performing fracture tests on specimens under wet [15] and cyclic loading [7] conditions. The present interface bond characterization study can be used to qualify adhesives, establish service performance, and obtain bond shear strength and fracture toughness values for interfaces of FRP-wood composite materials.
To effectively evaluate the in-service performance of bonded FRP-wood hybrid products and to qualify adhesive systems for FRP-wood bonding, the following general guidelines for interface bond characterization are suggested:
The ASTM D2559 wetting-and-drying cyclic delamination test [4] is sensitive enough to investigate key performance parameters, such as use of a coupling
agent (primer), open/closed assembly time, clamping pressure, bonding surface preparation, etc., and it can be first used as a screening test to evaluate the delamination of bonded interfaces.
Once the best combination of parameters is obtained from the ASTM D2559 tests, standard block-shear tests (ASTM D905) can then be used to evaluate average bond ‘‘shear’’ strength [4], which can be used in engineering design taking into account appropriate factors of safety. Also, the bond strength under various moisture contents (conditions) can be obtained.
Finally, the tapered double cantilever beam specimen [8] described in this study can be effectively used to obtain interface mode-I fracture toughness values under various environmental loadings (e. g., under dry and wet conditions [5,14,15]) and cyclic load conditions (fatigue fracture [7]); these data can be implemented in practical applications to assess the potential growth of a delamination crack at the FRP-wood interface.
This chapter presents a current status report on our research on FRP-wood interface bond. The qualification program is organized in two phases. First, the service performance and shear strength of adhesively bonded interfaces are evaluated by modified ASTM standard tests. The potential in-service delamination (or durability) is evaluated by a 3-cycle test involving repeated wetting and drying, and the wet and dry interface strengths are evaluated through ASTM block-shear tests. Next, the fracture toughness of the interface under dry and wet conditions and cyclic loading is measured by an innovative fracture mechanics test using the contoured or tapered double cantilever beam specimens. Several key parameters are studied, such as coupling agents (primers) to promote bonding, type of composite, open/closed assembly time, and clamping pressure. The characterization approach presented in this chapter can be efficiently used to establish the service performance and strength of FRP-wood interface bonds and to obtain fracture toughness data useful for delamination studies of bonded interfaces.
This study was partially sponsored by the United States Department of Agriculture under the National Research Initiative Competitive Grants Program (NRICGP-CSREES, Grant No. 98-35103-67579), the National Science Foundation (CMS 0002829 and CMS 9970008), and the West Virginia University Research Corp. Incentive Grant Program. The authors would like to acknowledge the valuable contributions of former and present graduate students: Uma M. Munipalli, Prabhu Madabhusi-Raman, Brent S. Trimble, Junhui Jia, David Boyajian, Jialai Wang, Shilpa Kodkani, and Yingwu Xu.
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