Consequently, although the actual load-displacement curves were used to calculate the stiffness (approximated here as the load-deflection curve
slope [DELTA]P/[DELTA]d), load-position curves were produced to illustrate the responses of individual specimens to the loading regime from the beginning to the ultimate fracture.
Figure 6(a) presents the load-midspan deflection curves of the lattice-web reinforced foam core sandwich panels with different web heights; the bending stiffness is calculated according to the slope of the load-deflection curve
. The stiffnesses of the sandwich panels with web heights of 75 mm (specimen TS75-75) and 100 mm (specimen TS75-100) increased by 100% and 88.8%, respectively, relative to specimen TS75-50 with a web height of 50 mm.
Inclination of load-deflection curve
from the ordinate axis is the smallest.
This is manifest as a long horizontal portion of the load-deflection curve
presented in Figure 4.
Load was applied in the inboard direction of the vehicle until a drop in load was observed in the load-deflection curve
. The drop in load occurred at 133% of the load requirement.
Empirically speaking and according to the ISO 9585 standard procedure, some conventional standard eight-hole plates were tested under the four-point bending test under ISO 9585 conditions, and their respective load-deflection curve
were compared with a curve obtained from a simulated model of similar geometry and properties (In regard to tables 1 and 2).
This must lie on a spring's load-deflection curve
, which is defined by the familiar Hooke's Law, F = -K x [chi], for linear displacement, where F is force, x is deflection, and K is the spring constant.)
Samples of the same diameter will show the same load at the same level of strain (% compression), but as the shape factor increases, so does the stiffness (slope of the load-deflection curve
The slope of the linear region of the load-deflection curve
was calculated in N/mm and assumed to reflect resistance of the passage of the screw through the foam.
A significant source of variability--and thus an area where extreme care is required--is in the analysis of the recorded load-deflection curve
for modulus calculation.
A resultant load-deflection curve
would give a composite picture showing how the test bar behaves during bending and reflect the intrinsic material properties and effects of physical dimensions of the test bar (width and thickness) and the testing apparatus setup (span).
In the precracking region, the load-deflection curve
was essentially a straight line defining full elastic behavior of the girders, and the girders were crack free.