بحث بعنوان Buckling Strength of Adhesively-Bonded Single and Double-Strap Repairs on Carbon-Epoxy Structures

بحث بعنوان Buckling Strength of Adhesively-Bonded Single and Double-Strap Repairs on Carbon-Epoxy Structures
اسم المؤلف
R.D.S.G. Campilho a,b,*, M.F.S.F. de Moura b, D.A. Ramantani b, J.J.L. Morais c, J.J.M.S. Domingues d
التاريخ
27 أبريل 2021
التصنيف
المشاهدات
320
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بحث بعنوان
Buckling Strength of Adhesively-Bonded Single and Double-Strap Repairs on Carbon-Epoxy Structures
R.D.S.G. Campilho a,b,*, M.F.S.F. de Moura b, D.A. Ramantani b, J.J.L. Morais c, J.J.M.S. Domingues d
a Departamento de Economia e Gestão, Universidade Lusófona do Porto, Rua Augusto Rosa, no. 24, 4000-098 Porto, Portugal
b Departamento de Engenharia Mecânica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal
c CITAB/UTAD, Departamento de Engenharias, Quinta de Prados, 5001-801 Vila Real, Portugal
d Departamento de Engenharia Mecânica, Instituto Superior de Engenharia do Porto, Rua Dr. António Bernardino de Almeida, no. 431, 4200-072 Porto, Portugal
Keywords:
C. Laminate
A. Carbon fibres
B. Fracture
C. Finite element analysis (FEA)
Cohesive zone model
a b s t r a c t
This work reports on an experimental and finite element method (FEM) parametric study of adhesivelybonded single and double-strap repairs on carbon-epoxy structures under buckling unrestrained compression. The influence of the overlap length and patch thickness was evaluated. This loading gains a particular significance from the additional characteristic mechanisms of structures under compression, such
as fibres microbuckling, for buckling restrained structures, or global buckling of the assembly, if no transverse restriction exists. The FEM analysis is based on the use of cohesive elements including mixed-mode
criteria to simulate a cohesive fracture of the adhesive layer. Trapezoidal laws in pure modes I and II were
used to account for the ductility of most structural adhesives. These laws were estimated for the adhesive
used from double cantilever beam (DCB) and end-notched flexure (ENF) tests, respectively, using an
inverse technique. The pure mode III cohesive law was equalled to the pure mode II one. Compression
failure in the laminates was predicted using a stress-based criterion. The accurate FEM predictions open
a good prospect for the reduction of the extensive experimentation in the design of carbon-epoxy repairs.
Design principles were also established for these repairs under buckling.
Concluding remarks
An experimental and finite element parametric study was performed on the behaviour of single and double-strap repairs of carbon-epoxy laminates under buckling unrestrained compression.
The influence of the overlap length and patch thickness on the failure modes, elastic stiffness and strength of the repairs was evaluated, to validate a finite element methodology to simulate
adhesively-bonded assemblies. This procedure used a trapezoidal
mixed-mode cohesive zone model to simulate the adhesive layer
and a stress-based criterion to predict compression failure in the
laminate. The cohesive laws of the adhesive layer in pure modes
I and II were estimated by an inverse method. The pure mode III
cohesive law was equalled to the pure mode II one. Results showed
that the finite element method can be a valuable predictive tool
and an option for the reduction of costs due to experimentation,
provided that suitable criteria are employed for the simulation of
the different types of fracture. Design principles were proposed
to execute single and double-strap repairs on composite structures
under compression, which should not be separated from the specific set of conditions selected for the repairs. For the range of overlap length (5–15 mm) and patch thickness values examined (0.6–
2.4 mm), the 15 mm overlap length double-strap repairs showed
the best results. Good results were also attained using double-strap
repairs with 10 mm of overlap length and values of patch thickness
between 1.2 and 2.4 mm, and also with single-strap repairs with an
overlap length of 15 mm.
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