Fracture testing methods

The fracture strength is commonly measured by applying a static load to membranes or cantilever beams. Due to the statistical nature of fracture processes, many tests have to be performed to obtain a statistically relevant result For membrane structures, knowing the burst pressure is essential. Section 5.5.5 presents several tensile-fracture testing methods for surface micromachined polysilicon cantilever beams. 

A relatively large quantity (approximately 200 gm) of an aromatic heterocyclic material was available and was used to develop a fracture test method that could be used to characterize materials limited in available quantities. This material is an acetylene-terminated polyimide, known as Thermid 600, which has the molecular structure shown in Figure 1. Although the material is a bit difficult to work with in the 100% solid form, this form was used to fabricate specimens. Cure kinetics and rheological data were measured and used to guide specimen fabrication. 

R.N. Parkins, A Critical Evaluation of Current Environment-Sensitive Fracture Test Methods, Environment-Sensitive Fracture Evaluation and Comparison of Test Methods, STP 821, ASTM, 1984... 

Injection-molded plaques of liquid crystalline polymers exhibit a multilayered structure through the thickness of a molding, where in each layer there is a high degree of orientation. Accordingly the fracture test methods of continuous fiber composites can be adopted for the testing of liquid crystalline polymers [176]. 

Anderson and others [18] have reviewed these and other fracture test methods for evaluating adhesive bonds. 

Procedures for performing valid fracture tests on polymers have been published [23] and besides containing details of specific fracture testing methods and procedures, criteria for the validity of the linear elastic assumption also are given. Some of the more common test geometries are shown in Figure 19.4. 

B K Neale and R H Priest, The unloading compliance method for crack length measurement using compact tension and precracked Charpy specimens, Elastic-Plastic Fracture Test Methods The User s Experience, ASTM STP856, F J Loss and E T Wessell, eds, American Society for Testing and Materials, Philadelphia, PA, 1985,375-393. 

G. Gogotsi, S. Mudrik, Fracture Barrier Estimation by the Edge Fracture Test Method, Ceram. Int., 35,1871-1875(2009). 

In addition to chemical analysis a number of physical and mechanical properties are employed to determine cemented carbide quaUty. Standard test methods employed by the iadustry for abrasive wear resistance, apparent grain size, apparent porosity, coercive force, compressive strength, density, fracture toughness, hardness, linear thermal expansion, magnetic permeabiUty, microstmcture, Poisson s ratio, transverse mpture strength, and Young s modulus are set forth by ASTM/ANSI and the ISO. 

Special-Purpose Resins, Repair Resins. Fractured acryflc dentures can be repaired with materials similar in composition to cold-cured denture resins. These materials generally cure more rapidly because of the relative simple manipulations involved. The process is quick and there is fltde dimensional change, but the strength of the repaired denture may be only half that of the original appliance (213). Test methods and requirements of these materials are given in ANSI/ADA specification no. 13 for denture cold-curing repair resins. 

ASTM-E 399-81 Standard test method Plane-strain fracture toughness of metallic materials... 

In TPE, the hard domains can act both as filler and intermolecular tie points thus, the toughness results from the inhibition of catastrophic failure from slow crack growth. Hard domains are effective fillers above a volume fraction of 0.2 and a size <100 nm [200]. The fracture energy of TPE is characteristic of the materials and independent of the test methods as observed for rubbers. It is, however, not a single-valued property and depends on the rate of tearing and test temperature [201]. The stress-strain properties of most TPEs have been described by the empirical Mooney-Rivlin equation... 

Cutwater, J. O., Murphy, M. C., Kumble, R. G. Berry, J. T. (1974). Double torsion techniques as a universal fracture toughness test method. Fracture Toughness and Slow-Stable Cracking, ASTM Special Technical Publication 559, pp. 121-31, American Society for Testing and Materials. 

Static fluid loss measurements, which are the present standardized testing method, provide inadequate results for comparing fracturing fluid materials or for understanding the complex mechanisms of viscous fluid invasion, filter-cake formation, and filter-cake erosion [ 1806]. On the other hand, dynamic fluid loss studies have inadequately addressed the development of proper laboratory methods, which has led to erroneous and conflicting results. 

Linear combination of atomic orbitals (LCAO) method, 16 736 Linear condensation, in silanol polycondensation, 22 557-558 Linear congruential generator (LCG), 26 1002-1003 Linear copolymers, 7 610t Linear density, 19 742 of fibers, 11 166, 182 Linear dielectrics, 11 91 Linear elastic fracture mechanics (LEFM), 1 509-510 16 184 20 350 Linear ethoxylates, 23 537 Linear ethylene copolymers, 20 179-180 Linear-flow reactor (LFR) polymerization process, 23 394, 395, 396 Linear free energy relationship (LFER) methods, 16 753, 754 Linear higher a-olefins, 20 429 Linear internal olefins (LIOs), 17 724 Linear ion traps, 15 662 Linear kinetics, 9 612 Linear low density polyethylene (LLDPE), 10 596 17 724-725 20 179-211 24 267, 268. See also LLDPE entries a-olefin content in, 20 185-186 analytical and test methods for,... 

The test method may specify either a notched sample or an unnotched sample. If a notched specimen is specified, the dimensions of the notch are also given. Figure 15.31 is an example of these dimensions for a metal sample. In the Charpy test the notched sample is struck from behind the notch. In the Izod test the notch is facing the hammer. The notch, called a stress raiser, concentrates the stresses applied by the impact load. It makes the material brittle and increases the elastic limit in the notch area. Without the notch, many materials will bend without fracture, and the capacity to absorb energy will not be accurately determined. 

In many fracture tests, a splitting method was employed. Figures 8 to 10 schematically indicate three of the arrangements used. In Fig. 8, a slice, h cm thick, is separated from the rest of the solid by pushing in a wedge which may be as thin as 0.01 cm but may also be more robust and have one of various shapes also the part broken off may be as thick as the remainder. In Fig. 9, a plate, 2h cm thick and w cm wide, is split in the middle to the depth c cm, and the force /required to extend the fissure is measured. Figure 10 shows peeling a ribbon, h cm thick, is peeled off the main body of an identical solid. 

ASTM El820-99 Standard Test Method for Measurement of Fracture Toughness , 1999 Annual Book of ASTM Standard Volume 3.01 Metals-Mechanical Testing Elevated and Low-Temperature Tests Metallography, American Society for Testing and Materials, 1999. 

A number of methods have been applied to evaluate the experimental data recorded during the tests, and they may be classified into two types compliance method and direct fracture energy method. 

Mandell 3.F., Darwish, A.Y. and McGarry F.3. (1981). Fracture testing of injection-molded glass and carbon fiber-reinforced thermoplastics. In Testing Methods and Design Allowable for Fibrous Composites, ASTM STP 734 (C.C. Chamis ed.), ASTM, Philadelphia, PA, pp. 73 90. 

Moore, D., Pavan, A., and Williams, J. 2001. Fracture Mechanics Testing Methods for Polymers, Adhesives, and Composites. Elsevier, New York. 

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