Flexural probes

Flexure Mode. Figure 29 illustrates TMA data for a two-layer insulation wire coating. Using the knife-edged three-point bend flexure probe (67) accentuates the softening that occurs at the glass-transition temperature. It is remarkable that the softening of both the outer layer of polyester and the inner layer of poly(amide-imide) were easily detected. 

Fig. 29. Use of the TMA knife-edged flexure probe to determine the softening point of both the outer and inner coatings of a motor-winding wire (67).

Flexural probes measure deflection properties in three-point bending, such as flexural strength and modulus of stiff materials and fiber-reinforced composites... 

Flat bulk sample, bars Loading/unloading cycles Flexural probe (three-point bend) Significant load Linear displacement Time Temperature crosslink density Creep behavior Softening temperature, heat... 

Optical methods can also be utilized to track the displacement of samples surfaces. Various types of interferometers have been employed for measurements of this type, yielding accuracy in the surface displacement between 0.1 and 10-5 A [6,9,15]. Both single and double beam versions have been developed for measuring the d33 coefficient of bulk samples. Cubic samples can avoid some of the difficulties associated with sample flexure on actuation [9], In some cases, one of the probing beams can also be brought to the side of the sample, so that lateral and tangential displacements can be tracked simultaneously [15]. 

Thermomechanical analysis (TMA) is the measurement of dimensional changes (such as expansion, contraction, flexure, extension, and calorimetric expansion and contraction) in a material. It is measured by the movement of a probe which is in contact with the sample in order to determine temperature-related mechanical behaviour in the temperature range of 180-800 °C. This occurs as the sample is heated, cooled (temperature plot), or held at a constant temperature (time plot). It also measures linear or volumetric changes in the dimensions of a sample as a function of time and force. 

The creep/fatigue studies Involving a high performance silicon nitride were also initiated. In particular, the creep strain associated with both button-head tensile samples and four-point flexure samples was measured as a function of time and stress at 1370 C, In the case of the button-head tensile samples, a direct-contact capacitance extensometer was used to monitor the displacement during constant load tests. The deflection of the specimen midspan in the flexure samples was measured with respect to the Inner load points using a three-probe LVDT extensometer. Additional details of the experimental procedure are given elsewhere. 

In thermomechanical analysis (TMA), the change in mechanical properties is measured as a function of temperature and/or time. A probe in contact with the sample moves as the sample undergoes dimensional changes. The movement of the probe is measured with an LVDT. The sample deformations that can be measured are compression, penetration, extension, and flexure or bending. 

Thermomechanical analysis (TMA) measures the deformation of a material contacted hy a mechanical prohe, as a function of a controlled temperature program, or time at constant temperature. TMA experiments are generally conducted imder static loading with a variety of probe configurations in expansion, compression, penetration, tension, or flexime. In addition, various attachments are available to allow the instrument to operate in special modes, such as stress relaxation, creep, tensile loading of films and fibers, flexural loading, parallel-plate rheometry, and volume dilatometry. The type of probe used determines the mode of operation of the instrument, the manner in which stress is apphed to the sample, and the amount of that stress. 

A series of quartz probes are available that allow the TMA-7 to be used in a variety of different operating modes expansion, compression, flexure, extension, and dilatometer. 

A) Penetration B) Extension C) Flexure a) Sample b) Probe c) Clamps d) Load... 

In general, the output of a TMA measurement is a plot of sample dimension or dimensional change versus temperature or time recorded in expansion, compression, tension, or flexure. Expansion, compression, and tension experiments are the most common measurements. Table 4.3 summarizes some key TMA applications in different measurement modes using different sample probes. Details of these measurements are discussed further in Sections 4.6 and 4.7 of this chapter. In addition to these basic types of measurement shear and torsional modulus of films, fibers, laminates, and adhesives can be measured using specially designed probes. 

Miscanthus, a high yield, fast growing perennial grass with low mineral content, was put under a microscope to explore its potential as a source of natural and environmentally friendly fibers and polymers for composite manufacturing. The manipulation of miscanthus structural and thermal properties at 25°C < T < 550°C, as probed by SEM, DSC, TGA, and in situ diffuse reflectance-FTIR, suggested that composites with flexural strength as high as 65 MPa could be formulated without the addition of external polymers. 

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