Loading, impact

The pin Brinell tester takes the form of a large C clamp with the baU indenter on the end of the screw. Load is controUed by a built-in shear pin. A modification of this device employs impact loading by a hammer to achieve similar results. 

A number of amorphous thermoplastics are presently employed as matrices in long fiber composites, including polyethersulfone (PES), polysulfone (PSU), and polyetherimide (PEI). AH offer superior resistance to impact loading and higher interlaminar fracture toughnesses than do most epoxies. However, the amorphous nature of such polymers results in a lower solvent resistance, clearly a limitation if composites based on such polymers are to be used in aggressive environments. 

G.T. Gray III and P.S. Follansbee, Influence of Peak Pressure and Pulse Duration on the Substructure Development and Threshold Stress Measurements in Shock-loaded Copper, in Impact Loading and Dynamic Behavior of Materials (edited by C.Y. Chiem, H.-D. Kunze, and L.W. Meyer), Deutsche Gesellschaft fuer Metall-kunde, Germany, 1988, 541 pp. 

J.E. Flinn, G.E. Duvall, G.R. Fowles, and R.F. Tinder, Initiation of Dislocation Multiplication in Lithium Fluoride Monocrystals Under Impact Loading, J. Appl. Phys. 46, 3752-3759 (1975). 

Finally, several chapters are provided which summarize the applications of shock-compression techniques to the study of material properties, and which illustrate the multidisciplinary nature of shock-wave applications. These applications include the inelastic response of materials, usually resulting from the extreme impact loads produced by colliding bodies, but also resulting from intense radiation loading. 

In this chapter the various approaches to the fracture of plastics are described and specific causes such as impact loading, creep and fatigue are described in detail. 

If Cm -I- 3Cii > 0, a centered simple wave will be produced by impact loading, and a record of this waveform suffices to determine the entire uniaxial stress-strain relation over the range of strains encountered. Vitreous silica is a material responding in this manner, and its coefficients have been determined by Barker and Hollenbach [70B01] (see also [72G02]) on the basis of a simple-wave analysis. 

Fig. 4.2. The technique used to study the piezoelectric behavior of the crystals quartz and lithium niobate used controlled, precise impact loading. The impact velocity can be measured to an accuracy of 0.1%, leading to the most precisely known condition in shock-compression science (after Davison and Graham [79D01]).

Fig. 4.5. The degree of approximation for the increase of current in time for uncoupled and weakly coupled solutions for impact-loaded, x-cut quartz and z-cut lithium niobate is shown by comparison to the numerically predicted, fully coupled case. In the figure, the initial current is set to the value of 1.0 at the measured value (after Davison and Graham [79D01]).

Fig. 4.7. The dielectric permittivity of impact-loaded dielectrics can be determined from current pulse measurements on disks biased with a voltage V. The magnitudes of the normalized current pulse values shown for two crystallographic orientations of sapphire are linear change with applied strain (after Graham and Ingram [68G05]).

Fig. 4X When x-cut quartz is subjected to impact loading whose duration is less than wave transit time, an anomalous current pulse can be observed after the stress release. The diagram shows locations at which experiments were conducted and delineates the region of normal and anomalous response (after Graham and Ingram ([72G03]).

Fig. 5.2. Current-versus-time records for x-cut quartz impact loaded to stresses of 2.5, 3.9, 4.5, 5.9, 6.5, and 9.0 GPa are shown, illustrating the drastic changes occurring with mechanical yielding and conduction. Time increases from right to left. The current pulses are in the center of each record and are characterized by a brief horizontal trace (zero current before impact) followed by a rapid jump to a current value (after Graham [74G01]).

A limited number of minus-x orientation samples were impact loaded in the vicinity of the Hugoniot elastic limit at stresses from 5.9 to 6.7 GPa. The principal observation of these experiments was that positive currents were observed from negative polarity disks when a stress of 5.9 GPa was exceeded. Such an observation confirms that quartz responds as predicted by the model, and that the elastic limit is in the vicinity of 6 GPa. 

Fig. 5.6. Typical current-time responses from impact-loaded PVDF are shown for samples on the standard materials indicated. In each record the upper traces are the full record showing short duration negative and positive current pulses due to loading and release in the standard. Time increases from left to right. The detail of each pulse depends upon the shock impedance of the materials. In each record, enlarged views of loading and release pulses are shown.

Fig. 5.21. The shock-induced polarization of polymers as studied under impact loading is shown. For the current pulse shown, time increases from left to right. The increase of current in time is due to finite strain and dielectric constant change. (See Graham [79G01]).

The toughness of a material is a design driver in many structures subjected to impact loading. For those materials that must function under a wide range of temperatures, the temperature dependence of the various material properties is often of primary concern. Other structures are subjected to wear or corrosion, so the resistance of a material to those attacks is an important part of the material choice. Thermal and electrical conductivity can be design drivers for some applications, so materials with proper ranges of behavior for those factors must be chosen. Similarly, the acoustical and thermal insulation characteristics of materials often dictate the choice of materials. 

Impact loading The loading resulting from sudden changes in the motion state of rig components. 

API Standard 4A (superseded by Standard 4F) provides rating of derrick capacities in terms of maximum safe load. This is simply the load capacity of a single leg multiplied by four. It does not account for pipe setback, wind loads, the number of lines between the crown block and the traveling block, the location of the dead line, or vibratory and impact loads. Thus, it is recommended that the maximum safe static load of derricks designed under Standard 4A exceed the derrick load as follows ... 

The manufacturer shall establish the reduced rated static hook loads for the same conditions under which the maximum rated static hook loads apply, but with the addition of the pipe-setback and sucker-rod loadings. The reduced rated static hook loads shall be expressed as percentages of the maximum rated static hook loads. Thus, the portable mast ratings in Standard 4D include a safety factor of 2 to allow for wind and impact loads, and require the manufacturer to specify further capacity reductions due to setback. 

Critical loads may be experienced for example, severe loads, impact loads such as jarring, pulling on stuck pipe, and/or operating at low temperatures. If in the judgment of the supervisor a critical load has occurred, or may occur, an on-the-job shutdown inspection equivalent to the periodic field inspection should be conducted before and after the occurrence of such loading. If critical... 

Ajar is a device for providing an impact load to the fish when the fish cannot be retrieved by normal string and derrick forces. There are purely mechanical jars and hydraulic Jars (see the section titled Drilling Bits and Downhole Tools for details on drilling Jars). In a fishing operation the Jar is usually placed... 

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