N Curve

A common form of societal risk measure is an F-N curve, which is normally presented as a cumulative distribution plot of frequency F... 

Figures 12 and 13 illustrate two of the more commonly used methods for displaying societal risk results (1) an F-N curve and (2) a risk profile. The F-N curve plots the cumulative frequencies of events causing N or more impacts, with the number of impacts (N) shown on the horizontal axis. With the F-N curve you can easily see the expected frequency of accidents that could harm greater than a specified number of people. F-N curve plots are almost always presented on logarithmic scales because of...

While the F-N curve is a cumulative illustration, the risk profile shows the expected frequency of accidents of a particular category or level of consequence. The diagonal line is a line of constant risk defined such that the product of expected frequency and consequence is a constant at each point along the line. " As the consequences of accidents go up, the expected frequency should go down in order for the risk to remain constant. As the example illustrates, if a portion of the histogram sticks its head up above the line (i.e., a particular type of accident contributes more than its fair share of the risk), then that risk is inconsistent with the risk presented by other accident types. (Note There is no requirement that you use a line of constant risk other more appropriate risk criteria for your application can be easily defined and displayed on the graph.)... 

The F-N curve, the risk profile, and the risk contour are the three most commonly used methods of graphically presenting risk results. Normally, you will elect to use more than one of these methods when evaluating risk estimates for decision making. 

Fig. 2-23 S-N curves for plain carbon steel in 0.05 M potassium hydrogen benzoate (pH 4) at 30°C at various potentials U U = rest potential).

F-N curve - A cumulative frequency number affected curve. 

Bogen-lampe, /. arc lamp, -lampenkohle, /. arc carbon, -licht, n. arc light, -linie, /. curved line, -mass, n. circular measure, -rohr, n., -rBhre, /. bent or curved pipe or tube, -schweisaung, /. arc welding, -skala, /. curved scale, -spektrum, n. arc spectrum. Stiic n. curved piece (Brewing) return bend,... 

Kurven-ast, m. branch of a (or the) curve, -bild, n. curve diagram, graph, -blatt, n. graph, -darstellung, /. graphic representation, -eck, n. angle in a curve, -gipfel, m. apex of a curve, -lineal, n. curved ruler, curved rule, French curve. 

Kurven-schar, /. group or system of curves, -schreiber, m. curve tracer, -zacke, /. iag (sharp change in direction) in a curve, -zeichnen, n. curve plotting. -zug, m. curve. 

The importance of the prevailing corrosion conditions in determining corrosion fatigue strength is further emphasised by the response of the S-N curve to electrochemical potential and in some instances corrosion... 

Fatigue data are normally presented as a plot of the stress (S) versus the number of cycles (N) that cause failure at that stress the data plotted defined as an S-N curve (Fig. 2-43). The use of an S-N curve is used to establish a fatigue endurance limit strength. The curve asymptotically approaches a parallel to the abscissa, thus indicating the endurance limit as the value that will produce failure. Below this limit the material is less susceptible to fatigue failure. 

Fig. 2-43 S-N curve establishes fatigue endurance limit strength.

Since fatigue cracks often start at a random surface imperfection, considerable scatter occurs in fatigue data, increasing with the increasing lifetime wherever crack initiation occupies most of the fatigue life of a specimen. When a line of the best fit is drawn from the available data points on an S-N curve, this represents the mean life expected at any given stress level or the stress that would cause, say, 50% of the product failures in a given number of cycles. 

Two conclusions can be drawn from an inspection of the S-N curve (1) the higher the applied material stress or strain, the fewer cycles the specimen can survive and (2) the curve gradually approaches a stress or strain level called the fatigue endurance limit below which the material is much less susceptible to fatigue failure. Different materials may... 

Endurance limit To develop S-N curves the fatigue specimen is loaded until, for example, the maximum stress in the sample is 275 MPa (40 ksi) (Fig. 2-43). At this stress level it may fail in only 10 cycles. These data are recorded and the stress level is then reduced to 206 MPa (30 ksi). Tliis specimen may not break until after 1,000 stress cycles at this rather low stress level. 

For below one monolayer the deposit may consist of an inhomogeneous mixture of a bare substrate and clusters approximately one monolayer thick. The state with the lowest chemical potential is represented by a line through the origin and tangent to the E[N) curve near the first local minimum, at Ni Nq. The slope of this tangent defines a chemical potential Thus, as N is increased from 0 to the fraction of the sub-... 

Note that most societal F-N curves extend out to hundreds or even thousands of fatalities. Such events involving process plant buildings are extremely unlikely, since few buildings, if any, within process facilities have such large concentrations of people. Aggregate risk curves should reflect site-specific conditions and realistic events. 

On simple inspection, it appears that the risks presented by the cafeteria exceed the company criteria. However, F-N curves are not always the most effective tools for identifying the major contributors to the risk. More detailed analysis, or use of other aggregate risk methodologies, such as determining expected numbers of fatalities per year, may reveal the risk to be more (or less) tolerable than that shown by the F-N curves. 

Section 4.2.2 discussed the use of methods other than F-N curves for determining aggregate risk. An aggregate risk measure can be calculated for Example 10 by multiplying each incident frequency by the expected number of serious injuries or fatalities. This results in a parameter of "fatalities per year."... 

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