Depth loading

The wide use of microhardness testing recently prompted Oliver (1993) to design a mechanical properties microprobe ( nanoprobe would have been a better name), which generates indentations considerably less than a micrometre in depth. Loads up to 120 mN (one mN 0.1 g weight) can be applied, but a tenth of that amount is commonly used and hardness is estimated by electronically measuring the depth of impression while the indentor is still in contact. This allows, inter alia, measurement... 

Depth loading The deposition of particles mainly within the filter interstices, rather than on the filter surface. Desiccator A sealed container containing a water-absorbing substance such as silica gel or calcium chloride used to dry test materials in the laboratory,... 

In the longer term, picoindentation instruments are likely to be widely used to extend the technique to a still smaller scale, with the help of techniques developed for atomic force microscopy. Already, plastic deformation at depths of a few atomic layers, as well as the effect of surface forces, have been quantified by means of depth-load measurements, using a point force microscope, i.e. an AFM operated in static (non-scanning) mode (Burnham Colton, 1989). 

Depth loading Fair Fair Poor Poor Poor Good Good... 

TABLE 8.9 Footing Shape, Footing Depth, Load Inclination, Foundation Ground (Slope) Inclination (Slope), and Footing Base Inclination Factors for Equations 8.20 and 8.21... 

Mat.-No. 1.5403, 1.6310) was developed in demineralised water with oxygen contents of 10 mg/1 and 5-6 mg/1 at a water temperature of 93 °C. The potentials that were ascertained were discussed as a function of crack depth, load frequencies, wave form and oxygen content. Subsequently, the potential differences between the metal surface and the crack tip increased with decreasing load frequency and for higher oxygen contents higher potential differences were also found (60 as opposed to 10 mV) [37]. 

The diesel generator buildings features include two standby diesel generators supplying power to priority defence-in-depth loads in the event of loss-of-normal power from ac power sources preferred and the maintenanee. Only one standby diesel generator is needed to fulfill this defence-in-depth duty. 

The combination of different electret treatment pattems/charge distributions means that the electret filters are not created equal filters combining mechanical and electret filtration mechanisms would thus better be a depth-loading media with a density gradient structure to help achieve reduced airflow resistance, enhanced dust loading, and prevention of face loading of the filter. ... 

The technological importance of thin films in snch areas as semicondnctor devices and sensors has led to a demand for mechanical property infonnation for these systems. Measuring the elastic modnlns for thin films is mnch harder than the corresponding measurement for bnlk samples, since the results obtained by traditional indentation methods are strongly perturbed by the properties of the substrate material. Additionally, the behaviour of the film under conditions of low load, which is necessary for the measnrement of thin-film properties, is strongly inflnenced by surface forces [75]. Since the force microscope is both sensitive to surface forces and has extremely high depth resolntion, it shows considerable promise as a teclnhqne for the mechanical characterization of thin films. 

Knoop developed an accepted method of measuring abrasive hardness using a diamond indenter of pyramidal shape and forcing it into the material to be evaluated with a fixed, often 100-g, load. The depth of penetration is then determined from the length and width of the indentation produced. Unlike WoodeU s method, Knoop values are static and primarily measure resistance to plastic flow and surface deformation. Variables such as load, temperature, and environment, which affect determination of hardness by the Knoop procedure, have been examined in detail (9). 

Fig. 2. Induction heating cod and load showing (a), current distribution in load, and (b), reference depth.

Fig. 3. Relative cod efficiency vs ratio of load diameter to reference depth.

A special coil configuration is used to heat thin strips of metal that caimot be heated efficiently with a coil that encircles the load, as the strip thickness is small compared to the depth of penetration. The transverse flux induction coil is positioned on either side of a strip to produce a uniformly heated strip with good efficiency in a much smaller space than conventional radiant or convective strip heating furnaces (6). 

The principle of the Rockwed hardness test is that the depth of the indentation between a minor and a major load appHed through an indenter is inversely proportional to the hardness number. Using a minor load to set the indenter helps to reduce backlash in the measuring system. 

The Rockwed testing machine is thus a framework permitting stable support of the workpiece on one side and means to impress the indenter under specified load on the other. A dial indicator attached to the indenter spindle is used to read directly the depth of indentation in hardness numbers. 

Depth filters are usually preferred for the most common type of microfiltration system, illustrated schematically in Figure 28. In this process design, called "dead-end" or "in-line" filtration, the entire fluid flow is forced through the membrane under pressure. As particulates accumulate on the membrane surface or in its interior, the pressure required to maintain the required flow increases until, at some point, the membrane must be replaced. The useful life of the membrane is proportional to the particulate loading of the feed solution. In-line microfiltration of solutions as a final polishing step prior to use is a typical apphcation (66,67). 

Penetration—Indentation. Penetration and indentation tests have long been used to characterize viscoelastic materials such as asphalt, mbber, plastics, and coatings. The basic test consists of pressing an indentor of prescribed geometry against the test surface. Most instmments have an indenting tip, eg, cone, needle, or hemisphere, attached to a short rod that is held vertically. The load is controlled at some constant value, and the time of indentation is specified the size or depth of the indentation is measured. Instmments have been built which allow loads as low as 10 N with penetration depths less than mm. The entire experiment is carried out in the vacuum chamber of a scanning electron microscope with which the penetration is monitored (248). 

Design criteria for carbon adsorption include type and concentration of contaminant, hydrauhc loading, bed depth, and contact time. Typical ranges are 1.4—6.8 L/s/m for hydrauhc loading, 1.5—9.1 m for bed depth, and 10—50 minutes for contact time (1). The adsorption capacity for a particular compound or mixed waste stream can be deterrnined as an adsorption isotherm and pilot tested. The adsorption isotherm relates the observed effluent concentration to the amount of material adsorbed per mass of carbon. 

Filter type Wastewater Filter depth, m HydrauUc loading, L/(min-m ) SS BO D SS BO D... 

Anaerobic ponds are loaded such that anaerobic conditions prevail throughout the Hquid volume. One of the major problems with anaerobic ponds is the generation of odors. The odor problem can frequentiy be eliminated by the addition of sodium nitrate at a dosage equal to 20% of the appHed oxygen demand. An alternative is the use of a stratified facultative lagoon, in which aerators are suspended 3 meters below the Hquid surface in order to maintain aerobic surface conditions, with anaerobic digestion occurring at the lower depths. 

Hardness is determined by measuring the penetration (depth or area) when a harder material, such as diamond, is pushed into the surface of the material of interest under a specified load. Tme hardness is defined as the force divided by the projected area. Vickers hardness tests, which employ a pyramid-shaped indentor, are frequently used to characterize ceramics however, Vickers hardness calculations normally employ total surface area rather than projected area (43). Measurements are made on the diamond impression shown in Figure 6. Vickers hardness is calculated using... 

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