a 228.8 mm (9 in) length. The specimens were allowed to cure for at least 24 hours before testing. A photograph of a test specimen is shown in Figure 3.
Experimental Setup and Procedures
/hr). The temperature of the oven was controlled us- ing a 2216 Eurotherm model 1D1-16-230 control system. This system controls the temperature using a 230V, 3000W heating coil at 14.6 Amps. A cooling system, consisting of copper tubing through which cold water was circulated, was added to the oven to cool the system after a test at el- evated temperature. The use of a separate cooling system allows the specimen to cool in an oxygen-free environment over a range of cooling rates.
, a method for measuring the elastic
A schematic of the three-point bend apparatus is shown in Figure 4. The three-point bend apparatus was placed inside a model OH-O1O-F1_CO-12-12-18 Thermcraft oven ca- pable of reaching 538C (1,000F). The oven was purged of oxygen using nitrogen from a tank at a flow rate of 1 m3 (35 ft3
/hr
tem, a load cell (Omega LC703-50) was installed to mea- sure the applied force. The cantilever system consisted of a wooden board that was connected by a hinge to the table on which the oven rested. A hanging mass at the opposite end of the hinge provided the loading force for the system. The load was controlled with an eye and hook turnbuckle that supported the cantilever. Using a simple wrench, the load could be increased and decreased in a rapid fashion.
Two Type K thermocouples were used to measure the sur- face and center temperature of a separate “dummy” speci- men located at the same elevation in the oven as the test specimen. A dummy specimen was used in order to keep the test specimen free of any modifications.
The three-point bend test fixture was designed to follow ASTM Standard D59347
modulus of thermoplastics and thermosetting plastics. The support and loading heads were made from 12.54 mm (0.5 in) diameter cylindrical steel bars. The bars provide enough surface area to prevent any indentation caused by the load- ing or support heads. The support heads were welded to a base plate to ensure a constant support span of 190.56 mm (7.5 in). This distance between the supports results in an overhang of the specimens that is sufficient to avoid slip- ping. The loading head was aligned using a guide that was welded to the base plate. The guide ensures consistent place- ment of the loading head in order to reduce variability in the elastic modulus measurements.
Specimen deflection was measured using two Omega LD610-5 linear variable differential transformers (LVDTs). The LVDTs were located outside the oven by suspending them from a ladder stand. Quartz rods were used to extend the LVDT probes into the oven through a port hole located above the fixture. The port hole was insulated with fiber- glass to protect the LVDTs from the oven when operated at high temperatures. One probe was situated on a table that straddles the specimen and rests on the support heads. This LVDT measured the displacement of the support heads. The loading head probe passed through a hole in the table and a tube that was welded to a small plate which, in turn, was placed on the loading head. This prevents the loading head probe from “walking” off the loading head and rendering the test invalid.
The specimen was loaded using a cantilever system located beneath the oven. The loading head was connected to the cantilever system using a series of mechanical connections exiting the oven through a port hole located directly beneath the test fixture. Between the port hole and the cantilever sys-
10
All devices were powered using an Elenco Precision De- luxe model XP-620 regulated power supply. The data was collected using a 16-bit IOtech 3005 Personal DAQ system connected to a laptop via USB. The software DasyLab was used to control the data acquisition system. A sampling fre- quency of 10 Hz, with an over-sampling rate of 8192, was used for all measurements. With these settings, each analog channel is sampled for 8,192 µs and a 16-bit average value over the scan period is returned.
The specimen deflection, D, was obtained by taking the difference between the displacements measured by the loading head and support head displacement LVDTs. The
Figure 4. Schematic of three-point bend experimental setup.
International Journal of Metalcasting/Fall 10
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85