1 - Safety factor (Strength of Materials, Mechanics)
(Old)
To
provide safe, reliable operation in the face of variations and
uncertainties, it is common practice to utilize a design safety factor
to assure that the minimum strength or capacity safely exceeds the
maximum stress or load for all foreseeable operating conditions. Safety
factors, always greater than 1, are usually chosen to have values that
lie in the range from about 1.15 to about 4 or 5, depending on
particular details of the application.
(Mechanical Design of Machine Elements and Machines, Jack A. Collins,Henry R. Busby,George H. Staab, p.7)
(New and better)
A safety factor is the dimensionless ratio of 'conscious over-design' that is either required, or actually applied to some part of a system.
Notes:
- A safety factor is used to communicate about risk. It is used to ensure that the design compensates adequately for both systems engineering and operational uncertainties.
- Historically, safety factors were applied to mechanical loads. We are using it here to describe the amount of safety margin we wish to have designed into the system. The target and constrained levels are specified at the required levels and then safety factor is applied to allow safety margins. (An assumption is being made here that there is only one safety factor involved; There could be several.)
- A safety factor is either prescribed by standards, such as engineering rules or policy, or it is specified at project level.
- A safety factor is a dimensionless ratio. Compared to a safety margin which is either expressed using units of measure (As it is the difference between two levels on a scale) or as a percentage value based on the required target or constrained level being %100.
- If we want to explicitly specify a safety factor, we can do so in a variety of ways using the safety factor parameter.
2 - Analysis of Variance (ANOVA) (Experimental Methods)
(Old)
Analysis of Variance is one of the most popular tests for numerical data and is useful for number of reasons. ANOVA is a general method of studying sampled-data relationships. ANOVA analysis allows the identification of variability from different potential sources. It sets up the analysis of the two sample means from our statistics. Analyzing variance allows for a testing of significant different between class means. The changes in the averages for the data group will be established using the ratio of two estimates of variance: between the groups and within the groups.
The ANOVA procedure is used instead of simpler t-test because significant differences exist in the size of sub-samples. Furthermore, preliminary analysis of descriptive statistics of each sample indicated significant differences in the standard deviations in some cases, again favoring ANOVA instead of simpler t-test.
(Islamic Commmercial Law and Economic Development, Zeeshan Javed Hafeez, p.14)
(New and Better)
The variation among physical observations is a common characteristic of all scientific measurements. This property of observations, that is, their failure to reproduce themselves exactly, arises from the necessity of taking the observations under different conditions. Thus, in a given experiment, readings may have to be taken by different persons at different periods of time or under different operating or experimental conditions. For example there may be a large number of external conditions over which the experimenter has no control. Many of these uncontrolled external conditions may not effect the results of the experiment to any significant degree. However, some of them may change the outcome of the experiment appreciably. Such external conditions are commonly known as the factors.
The analysis of variance methodology is concerned with the investigation of the factors likely to contribute significant effects, by suitable choice of experiments. It is a technique by which variations associated with different factors or defined sources maybe isolated and estimated. The procedure involves the division of total observed variation in the data into individual components attributable to various factors and those due to random or chance fluctuation, and performing test of significance to determine which factors influence the experiment.
(The analysis of variance: fixed, random, and mixed models Yazar: Hardeo Sahai,Mohammed I. Ageel, p. 1)
3 - Erichsen Test (Materials, Testing)
(Old)
This method is a so-called simulative test, as it mimics industrial deep drawing. The test is usually run on small sheet-metal blanks, which are shaped into cups; the size is generally much smaller than that used in industrial deep drawing. The punch head used in this test commonly has hemispherical shape. When it is pressed down into the sheet to create the cup, the bottom portion of the cup will of course also be hemispherical. Thus the bottom of the cup will be formed under balanced bi-axial conditions. The deformations taking place then will be out of the plane of the sheet specimen.
(Applied Metal Forming: Including FEM Analysis, Henry S. Valberg, p.438)
(New and better)
A destructive test to evaluate the ductility of sheet metal, it is also known as the cupping test or the Erichsen cupping test.
Application range ALL DUCTILE SHEET METALS
The procedure is that a ball of known diameter is impressed under a standard load on to a sample of sheet metal. This results in a cup being formed, of the approximate diameter and the depth of the diameter of the ball. On completion of the test, the cup produced is carefully examined for bursts or cracks or any wrinkling of the material locally which would indicate failure. Since this is a standard test, a system of comparing the material under test with previous batches is available to the inspector.
The test is a cheaper method than tensile testing, giving slightly more specialist information under certain circumstances. It cam be compared with the procedure now carried out by some users of high quality sheet metal in mass producing difficult pressings. There are occasions when such users reach an agreement with the metal suppliers that the metal in question must make a specific pressing. Each delivery is then tested by producing a pressing, and in the event of any defect appearing, the material will be rejected. Another method of accessing the suitability of sheet metal for deep drawing purposes is the ration of 'yield' or 'proof stress' to the 'ultimate tensile strength': the greater the difference, the better the material will be for deep drawing.
(Handbook of metal treatments and testing By Robert B. Ross, p.121)
4 - Swift Cup Test (Material testing)
(Old and better)
In the sweep cup test, a deep-drawn cup is used to determine the limiting draw ratio of blank size to cup diameter. It is obtained with a 50mm diameter flat bottom punch and a draw die appropriate for the thickness of the specimen. A circular blank is cut to a diameter smaller than the expected draw limit. Lubrication is provided by two oiled polyethylene disks, one on each side of the blank. The blank is drawn to maximum punch load, which occurs before the cup is fully formed. Successively larger blanks are drawn until one fractures before being drawn completely through the die. The diameter of the largest blank that can be drawn without fracturing, divided by cup diameter, determines the limiting draw ratio.
(Aluminum and Aluminum Alloys, ASM Specialty Handbook, p.232)
(New)
A simulative test for determining formability of sheet metal in which circular blanks of various diameters are clamped in a die ring and deep drawn into a cup by a flat bottomed cylindrical punch. The ratio of the largest blank diameter that can be drawn successfully to the cup diameter is known as the limiting drawing ratio (LDR) or deformation limit.
(ASM metals reference book By American Society for Metals, p. 87)
5 - Solenoid Operation (Electromechanics, Automation)
(Old)
An interesting aspect of solenoid operation is that it can HOLD a force with a small fraction of the current required to STROKE the same force through the length of its travel. Once the armature bottoms-out it's capable of holding many times the force needed to initially engage the pinion gear. Designers reasond correctly that the total electrical energy and size of solenoid required to operated a starter be reduced along with a small change in design.
Nuckolls B., Let's Talk About Starter Solenoids, p.1
(New and better)
Solenoid operation of hydraulic/pneumatic valves simplifies synchronization and/or sequencing of various motions used in machine tools. Pilot operation uses fluid power for operating valves. It is also used for actuating bigger hydraulic valves. A small solenoid operated valve can be used ti direct pressurized fluid to either end of the bigger valve, to move the valve. This eliminates the need for using bigger solenoid for shifting the heavier spool of a bigger valve. Pilot operation is also very convenient in sequencing fluid power actuators.
(Machine tools handbook: design and operation By P H Joshi, p. 554)
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