The aim of the article is to discuss the issue of strength of the circumferential backlash compensating beam in a high-efficiency gear pump. Three geometric versions of the compensating beam structure differing in the wrapping angle are analyzed. The mechanical model is solved assuming the curved beam model supported at the contact points between the beam and the gear teeth. The assumed mechanical structure is statically indeterminate. In order to determine the reactions in the supports and in the beam fixing, the Menabrei and Castigliano theorems are used. Based on analytical calculation results, the cause of compensation structure damage during experimental tests of prototype units is identified and the most favorable variant of beam structure, from the mechanical strength point of view, is determined.

This article presents theoretical and experimental calculations of the minimum thickness of a compensation lip used in external gear pumps. Pumps of this type are innovative technical solutions in which circumferential backlash (clearance) compensation is used to improve their volumetric and overall efficiency. However, constructing a prototype of such a pump requires long-lasting research, and the compensation lip is its key object, due to the fact that it is an element influenced by a notch and that it operates in unfavorable conditions of strong fatigue stresses. The theoretical calculations presented in this article are based on identifying maximum stress values in a fatigue cycle and on implementing the stress failure condition and the conditions related to the required value of the fatigue safety factor. The experimental research focuses on static bending tests of the lips as well as on the fatigue loading of the lips in series of tests at increasing stress values until lip failure due to fatigue. The tests allowed the minimum lip thickness to be found for the assumed number of fatigue cycles, which is 2.5 times the number of cycles used in wear margin tests.

This paper presents the results of durability tests of AW7075 aluminium alloy, which is widely used in producing high-durable and particularly reliable constructions in aeronautical and automotive industries. The plain-strain fracture toughness, depending on the orientation of fracture direction with respect to the rolling direction of the material, and the fatigue crack growth rate were determined. Based on scanning electron microscope (SEM) studies the two stages of fatigue fracture are shown: the first is plastic striations and the second is phenomenon of connecting micropores that were formed around intermetallic second phase particles. As a results of research a model of fatigue crack for the second stage is presented.

The articles presents a pilot study aimed to provide preliminary assessment concerning the effect of the low-energy plasma treatment on the level of internal stresses in welded plates. In addition, the article discusses the similarity of a stress relief mechanism based on annealing and that based on low-energy plasma treatment. The extensormetric measurements of internal stresses involving steel S355 after welding and after treatment in the plasma chamber revealed the low-energy plasma treatment-induced reduction of internal stresses.