Sliding planes of PTFE are normally used because of their incredible tribological homes. however, specifically in instances of high contact pressures, PTFE suffers from its comparatively negative mechanical residences. This paper affords a sliding production advanced inside an revolutionary experimental take a look at-setup to allow experimental investigation of large-scale concrete participants subjected to punching shear. to satisfy the unique needs of the brand new take a look at-setup, greased, handiest 0.5 mm skinny sheets of PTFE High Contact Pressures have been used to limit friction among the bearing construction and the test specimen. This enormously powerful sliding production ends in a dynamic friction coefficient μd,max between 0.0065 and zero.0035 even as the static friction coefficient μs remains below zero.0048. simultaneously, compressive axial stresses of extra than 60 MPa occur. The paper highlights fundamental aspects of the sliding plane’s improvement and demonstrates its sliding abilities.
Polytetrafluoroethylene (PTFE) is one of the maximum regularly used strong sliding substances inside the international. because of its unique tribological residences, PTFE is nowadays hooked up in a extensive variety of programs [1] [2] . in particular its very low friction coefficient, even for excessive contact pressures up to ninety MPa [3] , has made PTFE famous as an engineering material.
however, PTFE exhibits relatively bad mechanical houses and a high rate of damage. One way to improve the price of wear and the mechanical properties of PTFE is to incorporate filler substances which includes glass fibers, bronze or carbon. as an instance, Khedkar, et al. [4] and Conte, et al. [5] confirmed that fillers extensively growth the hardness and put on-resistance of PTFE-composites. however and in flip, its integration might also impair the tribological properties of PTFE, especially for excessive touch pressures.
In civil engineering in advance studies of Mark, et al. [6] and Vonk [7] have proven a extraordinary manner to enjoy the advantageous sliding traits of PTFE for excessive contact pressures. inside the framework of experimental investigations of concrete properties they used PTFE to allow a unfastened lateral extension on the loading plates in popular concrete cube assessments. Sheets of PTFE have been positioned among the loading High Contact Pressures plates and a concrete check member. To account for an basically decrease young’s modulus of PTFE in comparison to concrete, very thin sheets of PTFE with a thickness of zero.05 mm had been carried out (discern 1(a)). even as these skinny sheets decreased the affect on their take a look at outcomes correctly, experimental investigations with large sliding paths revealed instability of the sliding sheets along with a loss of sliding abilities.
although, PTFE is also used in case of appreciably more sliding paths. to be able to preserve its sliding skills, the thickness of the PTFE-sheets is then expanded. as an example, regular bridge bearings are ready with PTFE-sheets of approximately three – five mm thickness (figure 1(c)) [8] . consequently and especially because of the lower younger’s modulus of PTFE as compared to the metal additives of the bearing constructions, High Contact Pressures appreciably more deformations occur. Such deformations are desirable for bridge bearings due to surprisingly small axial stresses. however, in an progressive test-setup for concrete slabs subjected to punching shear presently developed at Ruhr-Universität Bochum in Germany, compressive stresses up to 64 MPa occur [9] – [11] . right here, the rotational rigidity required would no longer be glad with thick PTFE-sheets.
inside the the rest a sliding creation, essential for value effective punching shear tests of huge concrete slabs of realistic relevance, is delivered, that complies rotational tension in addition to enough shape balance. The basic concept of this new experimental take a look at-setup is the application of the nice practice in numerical investigations. by way of utilising symmetry situations, take a look at loads, physical dimensions and self-weights are substantially reduced. As a result, drastically large slabs may be tested with present check infrastructure.
Prerequisite of this concept is the improvement of a High Contact Pressures symmetry bearing to satisfy the symmetry conditions at the symmetry traces of a punching test. therefore, a bearing construction allowing nearly frictionless sliding in vertical and horizontal directions as well as a rotational stress (nearly no deformability) must be installed.
Sliding planes of greased PTFE have verified to be appropriate in this regard because they show high-quality tribological properties inspite of high compressive axial stresses. within the development process, PTFE-sheets of 0.5 mm thickness have proved to be especially suitable (figure 1(b)). The cause of this paper is to focus on the important improvement steps of this sliding construction as well as to provide the sliding competencies executed.