Testing, mechanical

Another quantity of interest which we can obtain from the dynamic mechanical testing is the complex viscosity t. It has the following correlations between the various material functions  

The importance of t] is that many polymers obey the Cox-Merz rule,05) which states that T] (a)) = T](7) when co (rad/sec) = y (sec). Thus, dynamic shear measurements may be useful for estimating steady shear viscosity [t] (7)] for crosslinked polymer systems since it has the following correlations06)  

A log-log plot of G (co) and G (co) versus co must have slopes of 1 and 2, respectively, in the regime of linear viscoelastic response. 

we would like to explain some of the details of our experimental technique because there are difficulties in handling these amorphous systems, most of which are pressure-sensitive adhesives at room temperature. For our work we used a dynamic spectrometer manufactured by Rheometrics Inc. (RDS). Both the parallel-plate and torsional-rectangular sample geometries were used initially, and we employed both temperature and frequency sweeps to obtain our data. The details of our testing technique are presented below. 

The form factor for a 25-mm-diameter disk, 2-mm thick, is too high at about 20,000. It is satisfactory for maximum modulus values of about 10 dyn/cm. The usual approach to accurately measure modulus values greater than 10 dyn/cm is to obtain measurements on long samples, such as rods or bars, which allow significant deformation at reasonable forces. The rectangular sample, which is approximately 2i x i wide, has a form factor of about 1. This can be used to measure samples in the modulus range greater than 10 dyn/cm. However, it is very difficult to prepare a bar of a pressure-sensitive adhesive at room temperature. Therefore, a small parallel-plate fixture, one which is only about 8 mm in diameter, was employed for all our measurements. 

The combined effect of the chemical and physical environment and stress on a polymeric material can be described in terms of a feedback, as the chemical and physical changes during exposure to UV-irradiation and oxygen 

Changes of morphology and particularly of orientation act as negative or inverse feedback, because orientation acts as a negative or inverse feedback and orientational strengthening and plastically deformed zones at crack tips paralyse the progress of fracture and deformation [2319]. 

Photodegradation causes the deterioration of mechanical characteristics, cracking and eventually complete disintegration of the material. The ultimate mechanical characteristics (especially elongation and break) of polymers are 

The deterioration of mechanical and rheological properties observed during photodegradation of polymers can be measured as changes in tensile strength and elongation (Fig. 10.110). 

The deterioration of mechanical properties is normally assessed by measurements of fracture resistance by pendulum impact test methods or slow speed flexural strength measurements and by ensuring that the surface of the specimens subjected to tensile stresses corresponds to the face exposed to the UV (or weathering) source. These tests are generally more meaningful than nondestructive tests, such as modulus measurements, since the chemical changes and the creation of fine cracks (often invisible to the naked eye) may involve only a very fine layer on the surface of the exposed samples. 

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GFC (Groupement Francois de Coordination pour le developpement des essais de performances des lubrifiants et des combustibles pour moteurs) the membership of which includes petroleum companies, additive manufacturers, automobile manufacturers and a few consumers. The GFC is interested mainly in mechanical testing. 

R. H. Mark, Handbook of Physical and Mechanical Testing of Paper and Paperboard, Marcel Dekker, Inc., New York. 

Nondestmctive testing (qv) can iaclude any test that does not damage the plastic piece beyond its iatended use, such as visual and, ia some cases, mechanical tests. However, the term is normally used to describe x-ray, auclear source, ultrasonics, atomic emission, as well as some optical and infrared techniques for polymers. Nondestmctive testing is used to determine cracks, voids, inclusions, delamination, contamination, lack of cure, anisotropy, residual stresses, and defective bonds or welds in materials. 

Mechanical Behavior of Materials. Different kinds of materials respond differently when they undergo basic mechanical tests. This is illustrated in Eigure 15, which shows stress—strain diagrams for purely viscous and purely elastic materials. With the former, the stress is reheved by viscous flow and is independent of strain. With the latter, there is a direct dependence of stress on strain and the ratio of the two is the modulus E (or G). 

Rheometric Scientific markets several devices designed for characterizing viscoelastic fluids. These instmments measure the response of a Hquid to sinusoidal oscillatory motion to determine dynamic viscosity as well as storage and loss moduH. The Rheometric Scientific line includes a fluids spectrometer (RFS-II), a dynamic spectrometer (RDS-7700 series II), and a mechanical spectrometer (RMS-800). The fluids spectrometer is designed for fairly low viscosity materials. The dynamic spectrometer can be used to test soHds, melts, and Hquids at frequencies from 10 to 500 rad/s and as a function of strain ampHtude and temperature. It is a stripped down version of the extremely versatile mechanical spectrometer, which is both a dynamic viscometer and a dynamic mechanical testing device. The RMS-800 can carry out measurements under rotational shear, oscillatory shear, torsional motion, and tension compression, as well as normal stress measurements. Step strain, creep, and creep recovery modes are also available. It is used on a wide range of materials, including adhesives, pastes, mbber, and plastics. 

Analysis methods for hydrogen absorbed in the deposit have been described (65), and instmments are commercially available to detect hydrogen in metals. Several working tests have been devised that put plated specimens under strain and measure the time to failure. A method for cadmium-plated work has been described (66) as has a mechanical test method for evaluating treatments on AlSl 4340 Steel (67). Additional information on testing for hydrogen embrittlement is also available (68). 

If there is a spare rotor sold with the order, the spare rotor is also heat cycled. If the customer requests, it too can be mechanically tested prior to shipment. If a motor drive is required, the initial run-up is... 

Mechanical testing of the non-lubricated helical-lobe compressors is modified from the previously described lest. For example, API 619 only requires a two-hour mechanical run. The procedures and monitoring requirements are generally the same as previously described. A run comparable to the overspeed run is the heat run. The compressor is run on air at the maximum allowable speed, and the discharge temperature is allowed to stabilize at a value 20°F higher than the rated discharge temperature. The compressor is then run for 30 minutes. 

As an alternative, used when the cost of the extra running does not warrant mechanical testing of both rotors, the spare rotor can be fitted to the case and only clearance measurements taken. This is philosophically similar to the reciprocating compressor bar over test. 

Neal, D. F, Centrifugal Compressor Mechanical Testing, Pre.sented at The Third Compressor Train Reliability Symposium sponsored by 1 ngi necring Advisory Committee, Manufacturing Chemists Association. April, 1973. 

TURNER, s.. Mechanical Testing of Plastics, liiffe, London (1973)... 

Portable fire extinguishers. Constiaiction, resistance to pressure, mechanical tests. With BS EN 3 Parts 1 to 6, BS 7863, superseded BS 5423 1987 (still cuiTcnt)... 

In a mechanical test, interfacial strength may be quantified in terms of either the minimum load required for interface disruption or the total integral energy or work expended. In many situations, due to non-uniformity of chemical or morphological conditions over the area of the interface or to non-uniformity of the applied stress in a given test [7], the two criteria are different. The investigator must thus strive to minimize or deal with both of the above complications, i.e. the interfaces studied should be chemically and morphologically uniform, and the stresses applied in the test should be uniform or distributed in way which is quantitatively describable. 

It is only in the context of the systematic variation of the properties of the adhesive and/or the adherend surface in a set of otherwise identical specimens subjected to a given mechanical testing procedure that it is reasonable to think of predicting relative interfacial strength. 

Fig. 2. Results of interfacial shear strength measurements of the same fiber/matrix systems using four different micro-mechanical tests during a round-robin program involving 12 different laboratories, (a) Results for untreated, unsized carbon fibers, (b) Results for carbon fibers with the standard level of surface treatment. Redrawn from ref. [13].

At least 11 repetitions of the mechanical test were made for each silane. 

As is true for macroscopic adhesion and mechanical testing experiments, nanoscale measurements do not a priori sense the intrinsic properties of surfaces or adhesive junctions. Instead, the measurements reflect a combination of interfacial chemistry (surface energy, covalent bonding), mechanics (elastic modulus, Poisson s ratio), and contact geometry (probe shape, radius). Furthermore, the probe/sample interaction may not only consist of elastic deformations, but may also include energy dissipation at the surface and/or in the bulk of the sample (or even within the measurement apparatus). Study of rate-dependent adhesion and mechanical properties is possible with both nanoindentation and... 

Hay, J.L. and Pharr, G.M., Instrumented indentation testing. In ASM Handbook Mechanical Testing and Evaluation. ASM International, Materials Park, OH, 2000. 

A more recent process, the P2 etch [60], which uses ferric sulfate as an oxidizer in place of sodium dichromate avoids the use of toxic chromates, but still provides a similar oxide surface morphology (Fig. 15) allowing a mechanically interlocked interface and strong bonding [9]. The P2 treatment has wide process parameter windows over a broad range of time-temperature-solution concentration conditions and mechanical testing confirms that P2-prepared surfaces are, at a minimum, equivalent to FPL-prepared specimens and only slightly inferior to PAA-prepared surfaces [61]. 

The simplest dynamic system to analyse is one in which the stress and strain are changing in a sinusoidal fashion. Fortunately this is probably the most common type of loading which occurs in practice and it is also the basic deformation mode used in dynamic mechanical testing of plastics. 

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