In modern times, it is necessary to offer reliable products to match the statutory directives concerning product liability and the high expectations of customers for durable devices. Furthermore, to maintain a high competitiveness, engineers need to know as accurately as possible how long their product will last and how to influence the life expectancy without expensive and time-consuming testing. As the components of a system are responsible for the system reliability, this paper introduces and evaluates calculation methods for life expectancy of common machine elements in technical systems. Subsequently, a method for the quantitative evaluation of the reliability of technical systems is proposed and applied to a heavy-duty power shift transmission.

The fatigue lifetime calculation of rolling bearings has been intensively researched in the past and has been well documented in standards. The majority of the conducted research in the field of bearing life expectancy only applies to bearings under continuously rotating conditions as can be found in many technical systems, such as vehicle transmissions. However, there are many other technical applications in which bearings perform oscillating motions, for which the fatigue life calculation is currently not standardized. For such oscillatory behaviour, there exist several modifications for the standardized lifetime calculation. The available modification approaches, however, assume purely sinusoidal oscillations. Thus, irregular non-sinusoidal oscillations require approximation with a simple sinusoidal oscillation to comply with the available approaches, which can lead to a loss of information. In this paper, a numerical calculation approach to modify the lifetime calculation for oscillating bearings underlying irregularly reversing speeds and varying loads is presented. The lifetime calculation results of this approach are compared to results of existing calculation approaches for fatigue life calculation of oscillating bearings. For this, the approaches are applied on simple sinusoidal speeds and loads. Subsequently, results of all calculation approaches are shown for irregularly varying speeds and loads, using the example of the drivetrain of an offshore crane winch with Active Heave Compensation (AHC). The calculation results indicate, that available lifetime modification approaches for oscillating bearings seem to overestimate the lifetime for irregularly oscillating conditions.

To match the high expectations and demands of customers for long-lasting machines, the development of reliable products is crucial. Furthermore, for reasons of competitiveness, it is necessary to know the future product lifetime as accurately as possible to avoid over-dimensioning. Additionally, a more detailed system understanding enables the designer to influence the life expectancy of the product without performing an extensive amount of expensive and time-consuming tests.In early development stages of new equipment only very basic information about the future system design, like the ratio or the system structure, is available. Nevertheless, a reliable lifetime prediction of the system components and subsequently of the system itself is necessary to evaluate possible design alternatives and to identify critical components beforehand. Lifetime predictions, however, require many parameters, which are often not known in these early stages.Therefore, this paper performs a sensitivity analysis on the drivetrain of an offshore winch with active heave compensation for two typical load cases. The influences of the parameters gear center distance and ambient temperature are investigated by varying the parameters within typical ranges and evaluating the quantitative effect on the lifetime.

Downtime of mobile machinery used in fields like construction, earthmoving or mining usually leads to an instant halt of an entire process and can even endanger entire operations. To meet the customer's requirement for high availabilities of their equipment, safeguarding the reliability of overall systems and components is necessary. Since life expectancy of systems and its components strongly depends on the experienced load history, this information needs to be available as accurately as possible to allow reliable lifetime calculation results. Due to the wide range of machines and applications of offhighway machines, determining representative loads is especially challenging. The challenges, in determining both load cycles for the entire system and local component loads, are discussed in this work, along with approaches to face them. Additionally, a method is described, which allows users to quantitatively calculate life expectancy of technical systems in both the concept phase and the later stages of the product life cycle. In the end, two examples are presented in which exemplary challenges are faced.

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