Underground Construction - December 2017 - 68

CIGMAT Report
the other hand, the yield strength increased with increasing strain rate
at 220C, but no variation was observed with increasing strain rate at 60
and 900C within the strain rate range studied. The ratio Esy/Ei varied
from 0.375 to 0.387 when the temperature increased from 22 to 900C
at a strain rate of 0.03 min-1. The ratio Esyo/Eio, at 220C varied from
0.282 to 0.360 when the strain rate was varied from 0.003 to 0.30
min-1, respectively.

In the case of GM, with a density of 0.79 g/cm3, it was observed that
the engineering tensile stress-strain relationship was nonlinear in both
elastic and inelastic domain, as shown in Figure 6(b). The initial yielding
was followed by nearly perfectly plastic state with some slight increase in
stress level near the fracture point in some cases. Quantifying the temperature effect, at the same strain rate, the overall stress level decreased
with increasing temperature; i.e. at a strain rate of 0.300 min-1 the yield
strength was 9.0 MPa at 220C and 4.0 MPa at 900C, a 56% decrease in
strength for about 300% increase in temperature. The stress level increased with increasing strain rate at all temperatures in the strain rate
range studied. The addition of glass microsphere to polypropylene decreased the yield strength and increased its thermal insulation properties.
The nonlinear behavior was more pronounced. The ratio Esy/Ei varied
from 0.167 to 0.120 when the temperature increased from 22 to 900C at a
strain rate of 0.03 min-1. The ratio Esyo/Eio, at 220C increased from 0.167
to 0.218 when the strain rate was increased from 0.03 to 0.30 min-1,
respectively.
GF engineering stress-strain relationships were nonlinear in both
elastic and inelastic domain, as shown in as shown in Figure 6(c). The
initial yielding was followed by a sudden drop in the stress level and a
steady decrease in the stress level, until fracture at all strain rates and
temperatures. Quantifying the temperature effect, at the same strain
rate, the yield strength decreased with increasing temperature. When the
strain rate was 0.300 min-1 the yield strength was 16.0 MPa at 220C and
6.8 MPa at 900C, a 58% decrease in strength for about 300% increase in
temperature. The stress level increased with increasing strain rate at all
temperatures within the strain rate range studied. Addition of 65% glass
filler to polypropylene decreased its yield strength and made the resulting
composite stiffer and more brittle at near-room temperature, 220C. The
modular ratio Esy/Ei decreased from 0.358 to 0.267 when the temperature increased from 22 to 900C at a strain rate of 0.03 min-1. The modular
ratio Esyo/Eio, at 220C, increased from 0.359 to 0.400 when the strain
rate was increased from 0.003 to 0.30 min-1.
In summary, pure polypropylene (PP) had the highest yield strength
at 220C and 900C temperature, followed by the polypropylene with 65%
glass filler (GF), as shown in Figure 8. GF had the highest elastic modulus,
and polypropylene with glass microsphere filler (GM) had the lowest elastic modulus. Addition of glass microsphere to polypropylene decreased
the elastic modulus. The same observations were recorded at the strain
rate of 0.300/min. Yield strengths were higher due to the strain rate level.

Conclusions

Figure 6: Engineering stress-strain relationships for (a) pure polypropylene (PP), (b)
glass microspheres filled polypropylene (GM), (c) glass filled polypropylene (GF).

ucononline.com

In this study, pure polypropylene, polypropylene with glass microsphere
filler and polypropylene with 65% glass fillers used as insulator coating
for deepwater pipelines were characterized using FT-IR and Scanning
Electron Microscope. The materials were characterized based on the bulk
density and tensile properties, with varying strain rates (0.003 to 0.300/
min) and temperatures (22ºC to 90ºC).
At least three samples were tested under each condition, and the density maximum coefficient of variations was 0.5% to 1.5% based on the
material type. Also, the maximum coefficient of variation for the tensile
yield strength, initial modulus and secant modulus was 2%, 4% and 3%,
respectively for all the tested materials.
Based on the experimental data and constitutive modeling of the behavior, the following conclusions are advanced:
* The pure polypropylene (PP), polypropylene with glass microsphere
filler (GM) and polypropylene with 65% glass filler (GF) engineering
Underground Construction December 2017

http://www.ucononline.com

Underground Construction - December 2017

Table of Contents for the Digital Edition of Underground Construction - December 2017