Abstract
The questions of design maintenance of a given fatigue longevity of rods of complex form during the intensification of load modes without changing of geometric, inertial and rigidity parameters of roads are considered. The study is conducted on the example of needles of circular machines with a small diameter of cylinder (automatic half-hose machines). An approach, based on the system of calculation of loads, loadings and resources under the criterion of fatigue strength, is proposed. The key link for the transition from the results of dynamic analysis to the determination of reliability indices is the dependence of limited longevity of needles on the cycles of load to fatigue failure with the use of statistical data on operating time to fatigue failure of the needles in production conditions. Since the random values of loads of the needles do not obey the normal law of distribution, the general description of density of distribution of amplitude of loads is presented. The influence of increase in speed parameters and constructive measures, aimed to reduce the corresponding loads at a current size of critical section of the needles, on the fatigue longevity is analyzed.
Highlights
IntroductionThe questions of longevity of rods of complex form on the example of knitting needles of circular machines of small diameter (automatic half-hose machines) are considered
The questions of longevity of rods of complex form on the example of knitting needles of circular machines of small diameter are considered
The study is conducted on the example of needles of circular machines with a small diameter of cylinder
Summary
The questions of longevity of rods of complex form on the example of knitting needles of circular machines of small diameter (automatic half-hose machines) are considered. The rods of the knitting needles have sections of a variable rectangular cross-section in length and a cylindrical hook in the zone of loop formation. Technological trajectories of the needles are given by a set of cams, which are called cams of knitting system. According to the results of the study of needle failures in production, the domination of hook destructions has been identified. Using the fractography analysis of surfaces of hook failures, the fatigue nature of destructions has been recorded [1, 2]. It is concluded that fatigue failures of needle hooks are the results of repeated action of repeated-variable loadings of the needle during the interaction with pitched cams that raise and lower the needles, and lateral cams, which braking needles on a given trajectory. The increase in stress in the critical section of the needle hook is affected by the reflection of waves when changing the sections in the needle rod
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