Disk on rod test

In this study, new experimental technique for the investigation of thermal shock fracture behavior, Disk-on-Rod test, is proposed. The temperature fields in the specimen were measured and used to calculate the 2 dimensional thermal stress field. 

In this study, for characterizing the thermal shock fracture process, new experimental technique, Disk-on-Rod test, was developed. An outline of the Disk-on-Rod test is shown in Figure 1. A thin disk specimen was heated to the required temperature by an infrared (IR) lamp and only the central part of disk was quenched by means of contacting with a metal rod. Since the disk specimen has a diameter of 20 mm and a thickness of 0.6 mm, and a contacting area has 4 mm diameter, 2-D thermal stress field was obtained. In order to characterize the fracture process, AE signals during thermal shock fracture were detected by an AE sensor attached on the bottom end of a metal rod, thus it was used for both coolant and wave guide. 

The apparatus of Disk-on-Rod test and AE measuring system are shown in Figure 2, schematically. The heated specimen was brought down with a holder and... 

Figure 2. Schematic Diagram of Disk on Rod Test System.

Figure 3. Thermal Stress Distribution during Disk on Rod Test (a) Radial Stress, (b) Tangential Stress.

Since the formation of maincrack could be observed at the AE increasing point, it is understood that the remarkable increase in AE corresponds to the main-crack formation due to microdamage accumulation. Then the critical stress for maincrack formation during thermal shock fracture, oth, can be determined by Disk-on-Rod test. Those values ranged from 220 to 330 MPa. The instantaneous crack path was not determined definitely because of its high growth velocity. Therefore, the thermal stress analysis is no longer valid after maincrack formation because the crack path could not be introduced into finite element models. 

These statistical approaches can not be applied directly to the experimental results in this study, because the fracture was occurred under biaxial stress in Disk-on-Rod tests and Piston-on-Ring tests. The statistical approaches for multiaxial stress state have been studied by several investigators. In order to determine the suitable equivalent stress more precisely, further investigation is needed for the widely variable stress states. However, it is considered that uniaxial statistical approach by eqs. (2) (5) are available for the comparison of the critical stress for maincrack formation under... 

In the present study, new experimental technique, Disk-on-Rod test, was developed and applied to the characterization of thermal shock fracture process in ceramics. The thermal stress fields were computed from temperature distributions measured by high-speed IR camera and fracture process was characterized by AE measurement, both of which are significant for understanding the thermal shock fracture behavior. 

Further investigation is needed for the application to complex multiaxial stress states and the fracture mechanical analysis of crack arrest and propagation process. However, new experimental technique of thermal shock fracture (Disk-on-Rod test), by which the indispensable information for the structural application of ceramics at high temperature, was established in the present study. 

There are several variants to this apparatus, which is based on a sample holder that oscillates up and down in the medium vessel. The sample holder may take the form of a disk, cylinder, or a spring on the end of a stainless steel or acrylic rod, or it may simply be the rod alone. The sample is attached to the outside of the sample holder either by virtue of being self-adhesive (e.g., transdermal delivery system) or is glued in place using a suitable adhesive. This apparatus may be used for transdermal products, coated drug delivery systems, or other suitable products (e.g., osmotic pump devices). It is prescribed for the drug-release testing of Psuedoephedrine hydrochloride extended-release tablets USP where the tablets are enclosed in a 5x5 cm of nylon, which is then attached to the rod. 

Test chemicals or chemical fractions can be dispensed from a variety of materials, depending on their volatility and solubility. Chemicals may be evaporated from such materials as glass rods or beads, metal surfaces, filter paper disks, cotton balls or wicks, rubber septa, polyethylene vials, glass capillary tubes, etc. It is important to ensure that the dispenser emits the compound at a fairly constant rate over the course of the assay. This may be more difficult for very volatile chemicals, thus, fresh dispensers uniformly prepared ahead of time may be required. This may be most important in the early stages of investigation where fractions of unknown composition and concentration are being used in a bioassay-driven fractionation scheme to isolate and, ultimately, identify specific chemical compounds eliciting particular behaviors. 

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