Tests mechanical

Many analytical techniques used to inspect the cited properties are common to the field of polymer characterization vibrational spectroscopy (ETIR, Raman), magnetic resonance spectroscopy (NMR, ESR) and liquid chromatography (GPC, HPLC). A few methods, such as oxygen consumption and chemiluminescence, are more specific to oxidative degradation. Mechanical tests are frequently used in combination with other analytical tools to asset the effects of degradation on mechanical properties. 

In thermal aging of polypropylene, for instance, a rapid transition from ductile to brittle behavior was observed before the appearance of carbonyl groups in the FTIR spectra. Recent data nevertheless indicate that some of the delay in C=0 buildup 

The morphology of these cracks depends on the type of polymer and the degradation conditions. Crack formation normally occurs on unstrained material according to the following sequence  

Oxidation of the superficial layer change in material density 

Oxidized polymers show an increase in density owing to the presence of polar functions. Densification of the degraded material creates internal stresses between the outer layer and the intact interior. Ultimately, cracks will appear when the mechanical strength of the degraded layer falls below the differentiial tensile stresses. Water absorption from ambient humidity or from rain, followed by surface evapo- 

In order to elucidate the influence of the modifications occurring on the composite surfaces, two adhesives were used. The first one (adhesive X) shows a poor adhesion with the composites used, and the second (adhesive Y) provides high-performance assemblies, with a predominantly cohesive failure in the composite at the initial stage. 

The mechanical behavior is quite different for the two adhesives (Fig. 20.6). Hence, the higher performance is not coming from the same surface treatment. 

In the case of adhesive X, the adhesive failure occurs principally for both untreated and peel ply treated surfaces. The corresponding improvement of lap 

In the light of these observations the interest of laser surface treatment is evident in terms of wettabihty, roughening, surface cleaning, and chemical modification. The use of two different adhesives makes it possible to check the relative effects of laser treatment on polymer modification as well as on fiber protrusion. When a cohesive failure inside the material is obtained after classical surface treatment, laser ablation makes it possible to improve the mechanical behavior by reaching the fiber reinforcement itself 

Adhesive bonding of anisotropic materials such as composites is comphcated as it is governed by numerous parameters. As a key issue, the surface parameters prior to bonding have to be correlated with the mechanical performance of the resulting assemblies. It is clearly established that apart from any additional surface treatment, the manufacture of the composite material itself strongly affects its adhesion ability. 

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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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