Design and Dimensioning Load Spectra
For designing and dimensioning a structural component or a structure, a design and dimensioning spectrum which covers the design life is required. The data which are acquired from a measurement constitute only an initial basis. Since the measurement exten
- PDF / 292,233 Bytes
- 11 Pages / 439.37 x 666.142 pts Page_size
- 44 Downloads / 222 Views
Design and Dimensioning Load Spectra
For designing and dimensioning a structural component or a structure, a design and dimensioning spectrum which covers the design life is required. The data which are acquired from a measurement constitute only an initial basis. Since the measurement extends only over a short period of time in comparison with the design life, an extrapolation is necessary. In particular, however, a preview over the so-called operational profile during the design life is necessary. If it is assumed that different operational states can occur, an assumption is also required for determining the frequency with which these states occur, for example start and stop procedures, idle time, or different states of operation. For making an assumption of this kind, many years of operational experience are required; the results of a single measurement are often not sufficient. For this purpose, partial spectra can be analysed for individual operational states, and the associated damage content can be evaluated by means of a Palmgren-Miner calculation. The purpose of the fatigue-life estimate is to obtain a relative estimate of the damage contribution from each state of operation, rather than a qualitative lifetime estimate. This can be accomplished with the use of a fictitious S-N curve, for instance, with the slope k ¼ 5 for bending and k ¼ 8 for torsion (Miner elementary, steel component). In correspondence with the severity of the risk associated with a case of damage, the operational profile can be varied in such a way that the load assumption results in a reasonable partial safety factor. A second partial safety factor results from the specification of the tolerable loading capacity (the strength). For machines and equipment which are manufactured in large series and which are employed in very different ways by the customer, the load assumption is often especially difficult. Bicycles, for instance, mountain bikes, are a prime example of such a problem complex. The loads acting on the bicycle fork, for example, depend on the weight of the cyclist, his manner of riding, on the type of terrain, and on details of construction such as the spring suspension. For which cyclist (recreation, not sport) is the bicycle to be designed and dimensioned? In this case, too, experience in the field is ultimately decisive for designing and dimensioning.
© Springer-Verlag GmbH Germany 2017 M. Ko¨hler et al., Load Assumption for Fatigue Design of Structures and Components, DOI 10.1007/978-3-642-55248-9_10
131
132
10
Design and Dimensioning Load Spectra
In the case of failure, material and production defects as well as faulty maintenance are often the first expected cause. Upon closer examination of the statistics on cases of failure, however, it becomes evident that many failures are the result of an incorrect load assumption and an erroneous determination of the local stresses. In plant designing, for example, it may be difficult to subsequently determine the load which actually occurred in a case of damage. Further
Data Loading...
