Beam test technique

The resonant beam test technique forms the basis of the ASTM Standard E756-83 for measuring the viscoelastic properties of damping materials. Fundamentally, the beam test requires that the resonant frequencies of a metal-beam, mounted in cantilever fashion, be determined as a function of temperature and frequency the beam is then coated with a polymer and the resonant frequencies and corresponding modal damping of the composite beam are determined as a function of temperature and frequency. From these two data sets, the vibration damping properties of the polymer can be evaluated. The ASTM Standard provides the necessary equations to obtain the complex modulus data from the collected test data and also provides guidelines for the proper choice of the specimens (1.21. The principal difference between the beam test and the other methods used here is that the beam test calculates the material properties from the test results on the metal beam and the composite beam whereas the... 

The coin-tap test is a widely used teclinique on thin filament winded beams for detection of disbonded and delaminated areas. However, since the sensitivity of this teclinique depends not only on the operator but also on the thickness of the inspected component, the coin-tap testing technique is most sensitive to defects positioned near the surface of the laminate. Therefore, it was decided to constructed a new scaimer for automated ultrasonic inspection of filament winded beams. A complete test rig illustrated in figure 6 was constructed in order to reduce the scanning time. While the beam rotates the probe is moved from one end to the other of the beam. When the scarming is complete it is saved on diskette and can then be evaluated on a PC. The scanner is controlled by the P-scan system, which enables the results to be presented in three dimensions (Top, Side and End view). 

The calculation of the PE surface is basically quantum mechanical. Accurate surfaces are used to show how the topography of the surface affects the reaction unit as it changes configuration across the surface. Predictions can be made, and these can be tested by molecular beams, spectroscopic techniques and chemiluminescence. 

Metastable muonium atoms in the 2s state have been produced with a beam foil technique at LAMPF and at the Tri University Meson Physics Facility (TRI-UMF) at Vancouver, Canada. Only moderate numbers of atoms could be obtained. The velocity resonance nature of the electron transfer reaction results in a muonium beam at keV energies. Very difficult and challenging experiments using electromagnetic transitions in excited states, particularly the 2 Si/2 2 Pi/2 classical Lamb shift and 2 Si/2-2 P3/2 splitting could be induced with microwaves. However, the achieved experimental accuracy at the 1.5 % level [18,19,20], does not represent a severe test of theory yet. 

The standard testing for SCC has been reviewed by Sedriks [9] and Turnbull [10]. The following techniques have been used to estimate the SCC surface flawed, cantilever bend, creviced bent-beam tests, double cantilever beam, and compact tension specimens. 

Interlaminar shear testing was carried out using the short beam shear technique in 3-point bending at a displacement rate of 0.02 /minute from room temperature to 1300 C. Results of the interlaminar shear strength [31] forthe 0/90° cross-ply Nicalon/BN/SiC/BS AS composites, containing 38-40 volume per cent of fibers are given in Table 5. The failure mode for all the test specimens was shear. 

There are numerous examples of the application of fracture mechanics to structural adhesive systems. Most notable are those of Mostovoy and his coworkers which have already been mentioned. " Bascom and coworkers have made significant contributions to the understanding of the effect of bondline thickness on fracture toughness. Kinloch and Shaw extend the work of Bascom to include rate effects and to develop mathematical models of the fracture resistance of adhesives. Hunston et al have used these methods to study viscoelastic behavior in the fracture process of structural adhesives.Mostovoy and Ripling used these techniques to determine the flaw tolerance of several adhesives,while Bascom and Cottington have studied the effect of flaws caused by air entrapment in structural adhesives." Finally it must be mentioned that one of the most simple, most widely used tests for strucural adhesives, the peel test, is actually a version of the double cantilever beam test. 

Several testing techniques are possible which use different specimen configurations, different loading modes, and various loading frequencies. Marceau et al. have described results for thick adherend lap shear and double cantilever beam (DCB) specimens exposed to 140 F/100%... 

As a result of these interlaboratory test programs, stancUud-ized test technique development has proceeded even slower than ever anticipated, realizing the difficulties encountered in defining acceptable levels of reproducibility and control of test variables. Since publication of the first edition of Manual 20, ASTM Standard G 168, Standard Practice for Making and Using Precracked Double Beam Stress Corrosion Specimens has been developed, a result of the interlaboratory program conducted on aluminum alloy 7075 [32]. 

Oblique incidence ultrasonic test techniques like those illustrated in Fig. 7 are also quite useful. In fact, it has been found in earlier studies that the normal beam shear wave incidence technique is often more sensitive to subtle interfacial weakness problems than a normal beam longitudinal incident wave. It is difficult, however, to produce shear wave incidence in a normal beam mode because of the somewhat permanent adherence to the substrate that is required. As a result, it was... 

Young s modulus may be measured by a beam-bending technique with a universal mechanical testing machine. For a three-point centrally loaded uniform beam, the elastic deflection 8 is related to the load F and the beam geometry through the relation... 

The first section of this entry deals with measurement of raw time-domain data and details the spatial filtering technique for data reductimi. The second section is devoted to feature extractirMi, and the third section deals with the diagnostics, both for damage detection and localization. The last section presents an experimental illustration of the SHM technique on a 3.78 m long steel I-beam tested in the laboratory. 

Mechanical property measurements of films on substrates are made using the beam deflection techniques discussed under stress measurement except that the beam is loaded with known weights and the deflection is measured with the stress as the known.[ l Measurements can oidy be made as long as the film does not microcrack (tension) or bhster (compression). ] Thin films have been shown to have very high elastic modulus and strength, presumably due to surface pinning of mobile defects (dislocations). An indentation test may be used to determine the elastic properties of coatings. ... 

Comment on collisional depolarization studies. The resonance fluorescence experiments described above have served to stimulate and test the development of recent sophisticated theories of collision broadening. However, the hope that new information on interatomic forces would be obtained by these experiments has not been realized. This is largely because the observed broadening is the mean effect of collisions averaged over all possible relative orientations and over the thermal velocity distribution of the ensemble. It may be that in the future more detailed information on the interatomic potentials could be obtained by combining tunable dye laser excitation and atomic beam scattering techniques. 

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