Taina Vuoristo

Dynamic compression testing of particle-reinforced polymer roll cover materials

Abstract Two polymer composite roll cover materials were studied using dynamic compression tests. The main focus was determination of viscoelastic properties of the materials and development of mathematical models to describe the behavior of these materials in the contact area between two rolls. The compression tests were conducted using short rise time pulses with different durations in servohydraulic materials testing machines. In the modeling, combinations of standard elastic and viscoelastic elements were used together with the Boltzmann superposition principle. A simple spring-dashpot model was found to fit sufficiently to the experimental data with relaxation (retardation) times ranging from a few milliseconds in transient loading tests to tens of hours in static compression tests

Effect of strain rate, moisture and temperature on the deformation behavior of polymer roll covers

Soft polymer roll covers, which are used in certain positions of paper manufacturing machines, have a vital role in the dynamics of two mating rotating rolls (i.e., nip dynamics). The polymer covers are often used in moist conditions where the loading rates are rather high and temperatures may vary from 45 to 60°C. In this paper, we study the dynamic mechanical behavior of two soft polyurethane composite roll covers under different conditions of temperature, moisture, and loading rate. For the tests in compression, both servohydraulic materials testing machines and the split Hopkinson pressure bar technique were used in the strain rate range of 0.001–1500 s−1. The specimens, which were to be tested under moist conditions, were immersed in paper machine water (pH 4.5) until saturated moisture content was reached. The materials showed remarkable softening as well as decrease in the strain rate sensitivity in moist conditions.

Multibody Analysis of Axially Elastic Rod Chains

Axially elastic rods are basic machine elements in hydraulic hammers, pilers and percussive drills [1]. The problem to analyze the motion history of such mechanisms is a very complex one, because the rods are simultaneously in large amplitude axial motion superimposed with a small amplitude elastic wave motion. The wave motion experiences division to reflected and transmitted components at each rod-rod interface depending on the current boundary stiffness [2]. The wave motion in each rod can be computed by finite elements or alternatively in space of semidefinite eigenfunctions. The feasibility of these methods in solving wave propagation problems in multi-rod systems with nonlinearly behaving rod-rod interfaces has been investigated and evaluated. The object of the experimental case study is a classical Hopkinson split bar apparatus [3] used in experimental analysis of material response to shock pulses. Another example representing a pile hammering system [4] evaluates the computational performance of the proposed approaches in long-term simulation of a complete work process.

Viscoelastic Wave Analysis of Hopkinson Split Bar System

Axially elastic rods are basic machine elements in hydraulic hammers, pilers and percussive drills. The problem to analyze the motion history of such mechanisms is a very complex one, because the rods are simultaneously in large amplitude axial motion superimposed with a small amplitude elastic wave motion. The wave motion experiences division to reflected and transmitted components at each rod-rod interface depending on the current boundary stiffness. The wave motion in each rod can be computed by finite elements or alternatively in space of semidefinite eigenfunctions. The feasibility of these methods in solving wave propagation problems in multi-rod systems with nonlinearly behaving rod-rod interfaces has been investigated and evaluated. The object of the case study is a classical Hopkinson split bar apparatus used in experimental analysis of material response to shock pulses.Copyright

Effects of Microstructure on the Dynamic Strain Aging in Ferritic-Pearlitic Steels

Effects of microstructure on the high strain rate high temperature mechanical response and dynamic strain aging of C45 and 27MnCr5 ferritic-pearlitic steels were studied using four different microstructural variants of the standard alloys. The high strain rate high temperature behavior of the steels was studied using a compression Split Hopkinson Pressure Bar device with high temperature testing capabilities. The steels were studied at strain rates up to 4500xa0s−1 and at temperatures from RT to 680xa0°C. Strong dynamic strain aging was observed for both steels in the studied temperature range. The results also show that the microstructure has a strong effect on the dynamic strain aging sensitivity of the steel. This is especially true at low plastic strains, where the effect of the microstructure is strongest. The effect of microstructure decreases as plastic strain increases. A coarse-grained microstructure showed the strongest dynamic strain aging sensitivity for both steels.

Monotonic Strength Properties of Siberian Yellow Pine

Strength values of the sapwood of Siberian yellow pine were measured in a system with orthogonal coordinates along the axial, radial, and tangential directions of the cell structure. Highest strength was the axial normal strength and lowest the tangential normal strength. The difference between these two values was 87-fold. Shear strength values remained between the two normal strength values. The highest shear strength appeared in tangential direction across the reinforcing fibers, i.e., on the plane perpendicular to the axial direction. Lowest shear strength appeared in tangential direction on the plane perpendicular to radial direction. The variations are due to orientation of cells and of fiber reinforcement in the cell wall laminas, especially in the middle layer of the secondary cell wall.