A Dual-Actuator Load Frame for Mixed-mode Fracture Testing of Laminated or Adhesively Bonded Specimens

David A. Dillard and Donatus OhanehiEngineering Science and Mechanics Department

Virginia Polytechnic Institute and State University

Sponsorship: National Science Foundation DMR-0415840

Intellectual Merit: A unique dual-actuator loading frame was developed with capabilities of providing an instantaneous and infinitely variable mode mix for fracture mechanics studies of adhesively bonded or laminated beam specimens. The design allows one to produce any desired combination of in-plane mode mixity with a single standard double cantilever beam specimen. The flexibility in mode mixity is achieved through use of two actuators driven by standard servo controllers, which may be independently operated at any desired amplitude and phase difference. To size the unit appropriately, a design space was created in which load and displacement restrictions can be superimposed in a fracture energy versus adherend stiffness space. This design space approach is expected to be a useful guide to instrument users and others for conducting fracture tests on laminated or bonded beam specimens. The instrument is fully operational and currently being used for testing. Acquisition & installation of an environmental chamber will complete the instrument.

Hydraulic Actuator

Bonded Sample

Clamp

Hydraulic Pump

G = 2000 J /m2

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0.01 0.1 1 10 100 1000 10000

EI (N-m2)

G (

N/

m2) 50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

13mm

16mm

Displacement,Δ=200mm lines

50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

Safe region for Aluminum alloy6061-T61,E = 70 GPaYield stress = 240 MPa

G = 2000 J /m2

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0.01 0.1 1 10 100 1000 10000

EI (N-m2)

G (

N/

m2) 50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

13mm

16mm

Displacement,Δ=200mm lines

50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

Safe region for Aluminum alloy6061-T61,E = 70 GPaYield stress = 240 MPa

G = 2000 J /m2

G = 2000 J /m2

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0.01 0.1 1 10 100 1000 10000

EI (N-m2)

G (

N/

m2) 50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

13mm

16mm

Displacement,Δ=200mm lines

50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

Safe region for Aluminum alloy6061-T61,E = 70 GPaYield stress = 240 MPa

G = 2000 J /m2

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0.01 0.1 1 10 100 1000 10000

EI (N-m2)

G (

N/

m2) 50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

13mm

16mm

Displacement,Δ=200mm lines

50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

Safe region for Aluminum alloy6061-T61,E = 70 GPaYield stress = 240 MPa

G = 2000 J /m2

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0.01 0.1 1 10 100 1000 10000

EI (N-m2)

G (

N/

m2) 50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

13mm

16mm

Displacement,Δ=200mm lines

50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

Safe region for Aluminum alloy6061-T61,E = 70 GPaYield stress = 240 MPa

G = 2000 J /m2

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0.01 0.1 1 10 100 1000 10000

EI (N-m2)

G (

N/

m2) 50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

13mm

16mm

Displacement,Δ=200mm lines

50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

Safe region for Aluminum alloy6061-T61,E = 70 GPaYield stress = 240 MPa

G = 2000 J /m2

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0.01 0.1 1 10 100 1000 10000

EI (N-m2)

G (

N/

m2) 50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

13mm

16mm

Displacement,Δ=200mm lines

50mm

100mm

150mm

200mm

250mm

50mm

100mm

250mm

150mm

1mm4mm

7mm

10mm

Load, P=10kNlines

Safe region for Aluminum alloy6061-T61,E = 70 GPaYield stress = 240 MPa

G = 2000 J /m2

Capabilities:• Ease of changing mode mixity while a test is

underway.• Mode mixity is infinitely variable from pure

mode I through any mode mixity to pure mode II.

• Data at various mode mixities obtained with a single specimen or specimen type.

• Capable of doing quasi-static, high frequency fatigue testing of adhesively bonded geometries.

• Conducting fracture tests on specimens held in a controlled temperature chamber, or submersed in a liquid environment.

• Systematically characterize fracture envelopes for adhesives and composites for design purposes.

Research Areas of Interest:

• Quasi-static crack growth and kinking

• Subcritical crack growth and kinking

• Effect of environmental degradation

• Effect of crack tip shielding on changing mode mixity

• Steering cracks away from weak regions

• Using aligned nanotubes for promoting adhesion

Broader Impact: Several students are participating in the experimental effort to utilize this instrument, obtaining

significant experience in fracture testing and analysis, finite element modeling of fracture events and crack propagation, and the effects of mode mixity, adherend surface pretreatment, and material durability. A conference presentation and journal article are currently being prepared to convey concept and instrument design. Plans are underway to utilize the instrument on several significant projects.

Specifications:• The dual-actuator unit is equipped with fatigue rated linear hydraulic actuators with a force

capacity of 2.5 kips and 4” (2”) stroke.

• A hydraulic service manifold, rated at 60 GPM and 3000 psi oil service, was used to interface the hydraulic supply to the actuators.

• A hydraulic power supply to provide fluid to the service manifold at a rate of 22 gallons per minute (GPM) and with 3000 psi pressure.

• TESTExpress® Digital Servocontroller equipped with a built in test compiler, 2 DC load conditioners, 2 AC stroke conditioners, 2 valve drivers, 4-waveshape function generator, Transducer interlocks, hydraulic power supply interface, including HPS start/Low/High, and overtemp and low level interlocks, and 8 channel A/D interface with 4 uncommitted A/D inputs, and data logging/reporting facility. to provide complete control of the servo-hydraulic actuator.

• The fracture testing on the dual-actuator unit is performed via LabVIEW codes designed specifically for each application.