Fracture standard physical testing

Fractured bulk polymers and composites require only coating with a conductive layer (Section 4.7.3) before observation in the SEM, although some composite fracture surfaces are so rough as to make deposition of a thin continuous conductive film very difficult. High resolution is rarely required in these materials so the common solution is to use a thick coating, and often carbon is evaporated followed by metal coating. Fibers, particularly textile fibers and thin films, have such a small cross sectional area that the main difficulty is in handling the broken sample. 

Hearle and Cross [294] broke thermoplastic fibers at normal rates of extension in an Instron and examined them in the SEM. They developed a special stub for mounting the fiber ends. A step was cut from the circular stub and an elliptical hole cut in the remaining stub and a screw placed in the cut step. This provides a space in the center of the stub for fibers to be mounted on double sided sticky tape. The screw is used to attach the cut step portion to the remainder of the stub. 

Studies have been conducted by breaking polymer fibers on devices, such as an Instron and then 

SE images of a matched pair of tensile failed PET fibers are shown in Fig. 4.30. A classical slow fracture zone, or mirror, is seen adjacent to the locus of failure. A typical ridged or hackle morphology is exhibited as the crack propagates and accelerates away from the failure locus. In this study, an inorganic residue from the polymer process was shown to be the cause of failure [295]. The value of such a fractography is that 

Multiphase polymers are observed by frac-tography for evaluation of the rubber or the dispersed phase size, shape and morphology. Bucknall [300] described the control of the 

Representative SEM images (Fig. 4.41) show a range of different multiphase polymers in notched Izod impact fractured specimens. A polymer with large, nonuniform, dispersed phase particles, not well adhered to the matrix, is shown in Fig. 4.41A. A much finer dispersed phase is shown in Fig. 4.41B with both particles and holes from particle pullouts. Smaller particles are not as obvious in Fig. 4.41 C, although the dispersed phase accounts for 15% of the specimen. Finally, the SEM image in Fig. 4.41 D does not reveal the elastomer, so the size and distribution of the dispersed phase must be provided by some other microscopy technique. 

Polymer matrices are also commonly reinforced with mineral fillers or fibers, such as calcium carbonate, talc, wollastonite, clay, and mica [506], and more recently fine additives are used to manufacture nanocomposites. Scanning electron microscopy images of fracture surfaces 

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Textile fiber fractography was initially developed at UMIST (University of Manchester Institute of Science and Technology), especially by Hearle. Fiber fractography and the classes of fracture were reviewed by Hearle and Simmens [15] and further defined later [29, 30]. These classes are shown in Table 5.1 with examples and appropriate references. The mechanism of fiber failure can be determined by fractography studies (Section 4.8.1) in the SEM. Typically, fibers broken during a standard physical test, such as... 

Determination of dispersed phase morphology is most often conducted by SEM of fractured specimens. Fractures are prepared by manual methods, after immersion in liquid nitrogen, or by standard physical testing procedures. The microstructure of the homopolymers should be examined for comparison with the multiphase polymer. SEI of an Izod fracture surface of a POM/PP copolymer is shown in Fig. 5.42. The two phases are incompatible, i.e. they are present as two distinct phases. The dispersed phase particles range from less than 0.5 to 2[xm in diameter. The sample fracture path follows the particle-matrix interface and holes remain where particles have pulled out of the matrix, showing there is little adhesion between the phases. 

Anew technique, laser induced decohesion spectroscopy, is presented, which is capable of measuring the practical work of adhesion between a transparent polymer coating or substrate. A laser pulse directed onto the sample creates a blister at the transparent/opaque interface. The blister s internal pressure depends on the laser pulse energy, and at a critical pressure the sample fractures, creating an annular debond similar to that obtained in the standard blister test. By measuring physical variables such as the... 

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. 

Proposed Method of Test for Plane Strain Fracture Toughness of Metallic Materials, ASTM Standards on Physical and Mechanical Testing of Metals Nondestructive Test. Part 31, ASTM International, West Conshohocken, PA, May 1969, pp. 1099-1114. 

Thermal cycle experiments have been the current industry standard for assessing second-level interconnect reliability. These t5q)es of tests tend to produce solder joint and solder joint-pad interfacial fractures that are t5q)icaUy seen in field failures. The fact that thermal cycle tests produce the same physical failures allows for detailed acceleration transformations and finite element-based Ufe assessments to be made employing thermal cycle data as input. 

Service lifetime prediction of polymers and/or polymer based materials may be undertaken from different types of tests, such as creep behavior tests (linear and non-linear creep, physical aging, time-dependent plasticity), fatigue behavior tests (stress transfer and normalized life prediction models, empirical fatigue theories, fracture mechanics theory and strength degradation) and standard accelerated aging tests (chemical resistance, thermal stability, liquid absorption) [32]. 

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