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Investigation of interface characteristics of single fiber model composites

Description

In the last decade several micromechanical measuring stations have been developed and set up to investigate the interface characteristics between fiber and matrix in composite materials. The experiments include quasistatic and high-speed pull-out tests, hysteresis and long-term loading tests as well as subcritical dynamic loading tests. In most cases, glass, carbon or aramid fibers embedded in a polymeric or cementitious matrix are used. The sample preparation equipment has also been developed at the IPF and is described in Fiber embedding. The principle setup of the experiments is shown in the adjacent picture. The vessel with matrix and embedded fiber is clamped on an actuator that generates the displacement. The fiber end protruding out of the matrix is glued on a mandrel that is fixed at a load cell. The equipment is specified by the experimental demands. A survey of the different methods is given in the table below.

Contact
Prof. Dr. E. Mäder (Composite Materials division)
Dr. W. Jenschke (Research Technology division)

  Quasistatic pull-out test Hysteresis and long-term loading test Dynamic loading test High-speed pull-out test
Measurement procedure: The fiber is slowly pulled out of the matrix with constant speed. The fiber-matrix composite is exposed to alternating stress (tensile, compressive or both). Depending on the frequency, the excitation function can be a variable load function or a sinusoidal load. The fiber-matrix composite is exposed to alternating stress (tensile, compressive or both) by sinusoidal excitation where frequency and/or amplitude are stepwise changed from an inital to a final value. The fiber is rapidly pulled out of the matrix in a split second.
Force meas.:
  Range:
  Resolution:
Piezo-resistive load cell
0 - 2.5 N
75 µN
Piezo-resistive load cell
0 - 2.5 N
75 µN
Piezo-electric quartz
0 - 50 N
0.1 mN
Piezo-electric quartz
0 - 50 N / 0 - 5 kN
0.1 mN / 2.5 mN
Displacement:
  Stroke:
  Resolution:
  Typ. displ.:
  Pull-out speed:
  Exc. freq.:
  Amplitude:
Micro-drive
50 mm
2 nm
300 µm
typical: 10 nm/s
-
-
Piezo-translator
120 µm
4 nm
8 µm
-
0.01 - 0.1 Hz / 5 - 20 Hz
0.5 - 5 µm
Piezo-translator
80 µm
1 nm
-
-
10 - 350 Hz
0.5 - 5 µm
Piezo-translator
180 µm
-
180 µm
max.: 10 000 µm/s
-
-
Issued parameters: Maximal force, E-module, strain work, shear stress, adhesion strength, energy release rate Hysteresis error, shear stress, shear strain, loss and storage work, phase angle between force and displacement curve, damping and stiffness Force amplitude and phase angle between force and displacement curve as a function of excitation frequency and amplitude Maximal force, E-module, strain work, shear stress, adhesion strength, energy release rate
Excitation function:
Force - displacement diagram: