WO2022125042A2

WO2022125042A2 - A machine for determining the lifetime of an elastic material

Info

Publication number: WO2022125042A2
Application number: PCT/TR2021/051369
Authority: WO
Inventors: Cihan CENGİZ
Original assignee: Tekno Kauçuk Sanayi̇ Anoni̇m Şi̇rketi̇
Priority date: 2020-12-08
Filing date: 2021-12-07
Publication date: 2022-06-16
Also published as: WO2022125042A3; DE112021005615T5

Abstract

The invention relates to a machine (1) for determining the fatigue life of the elastic materials (EM), comprising - an upper shaft (1.1) applying a stress (or a pressure) by being bent at the predetermined values of an angle to an elastic material (EM), a lower shaft (1.2) on which said elastic material (EM) is positioned and which rotates the elastic material (EM) around its own axis (a symmetry axis), a drive shaft (1.3) mounted to said lower shaft (1.2), a drive member (1.4) which rotates the drive shaft (1.3) at a predetermined rotation speed, a bending member (1.5) which enables the upper shaft (1.1) to apply a stress to the elastic material (EM) by bending the upper shaft (1.1) by a predetermined angle, a pushing member (1.6) which enables said bending member (1.5) to angle the upper shaft (1.1), and a detector (1.7) for measuring a force value formed by the elastic material (EM) in the opposite direction to the force applied thereto.

Description

A MACHINE FOR DETERMINING THE LIFETIME OF AN ELASTIC MATERIAL

Technical Field

The invention relates to a machine for determining the fatigue characteristics of an elastic material.

Prior Art

Determination of the fatigue characteristics of the materials provides information on the lifetime of a material. Thus, the determination of the fatigue lives of the materials is important. In the state of the art, there are a number of machines in order to determine the fatigue characteristics of the materials, such as metal and plastic. There are static and dynamic tests applied to the materials to determine the fatigue characteristic. When the material is tested under the slowly increasing static loads, the strength of the material failures, and the material breaks at a certain boundary strain. This stress value found is called the static strength of the material. Determination of the static test values are easier than the determination of the dynamic test values. The tests for the static loads are quite simple. Said tests are a tensile and breaking test under a certain load, and the force and distance are measures under that load. The standards and mode of the test are defined. As no material is defined except for the metals in the static tests in the state of the art, said tests provide good results for the metals. That is, this test provide correct results only for metal materials. Said test measures how long the metal materials resist under the same load. As the load is a force acting on the material, the strength of the material is observed under strain, stress and displacement by the force acting on the material. Thus, in the state of the art, there are machines (a fatigue testing machine, or a creep testing machine) performing static tests in order to determine the lifetime of a material in the metals.

The same measurement in the hard plastics is carried out by the machines (a flexibility testing machine) in the state of the art. In that test, the plastic materials are tried to be bent in varying displacement or force amplitudes. How long the plastic material resist under said displacement or force, hence the fatigue characteristic thereof is tested, and the lifetime of the plastic material is determined. In the state of the art, the characteristic features and fatigue strength of the materials, such as metal and plastic, are determined by the tests using standard bow-tie or coupon samples. Thus, a design may be made using the analytical or digital methods in order to achieve a certain function. The behavior of the designs made under certain loads and displacements may be calculated by the analytical and digital methods, as well as the fatigue strength under the repetitive loads may be calculated with fatigue curves obtained from the material tests. The stiffness of the elastic materials may be determined at a material level using the standard coupon or bow-tie samples. However, the fatigue strength of the elastic materials cannot be obtained in a material level, the behaviors of the designs made under the repetitive loads cannot be calculated. Therefore, there is a need for an expensive and time-consuming process to produce the products and to test the fatigue strengths thereof in order to verify the designs. The characterization of the fatigue strengths of the elastic materials at a material level is time- and cost-efficient for the designing and verifying processes of the elastic materials used in many sectors.

Apart from the hard plastic and metal materials, elastic, for example rubber parts are used in the industry, especially in the automotive industry, and these rubber parts operate under variable loads. The above-mentioned machines which operate based on the static test values of the metal or plastic materials do not have the same effects for the materials having dynamic test values, such as rubber. Thus, an accurate result cannot be obtained. The fatigue characteristics of said rubber material used in the automotive industry are difficult, or impossible to, determine with the machines used for the materials of metal and hard plastic. The machines developed to determine the lifetime of both metal materials and hard plastic materials are very expensive, and said machines used to test the lifetime are not used for rubber materials. Thus, the test methods of said machines are not used for the rubber materials in order to calculate the fatigue life of the metal and plastic materials. That is, the fatigue life of the rubber cannot be accurately calculated with the machines using this method. The fatigue life may substantially vary depending on the type of material. As the stiffness of the elastic materials is lower than that of the metal and plastic materials, the displacement amplitudes to which they are exposed under the similar loads are higher. Therefore, measurement machines which do not fall within the state of the art are needed to be developed in order to determine the fatigue characteristics, hence life, of a rubber material in an accurate manner. Brief Description of the Invention:

The object of the invention is to provide a machine for determining the fatigue characteristics, hence lifetime, of an elastic material, for example a rubber.

Another object of the invention is to determine the fatigue resistance of rubbers of varying types by said machine and to compare them with each other.

Said machine determines the lifetime of a rubber material in a quite accurate manner. To do this, the necessary fatigue data of the materials are determined by said machine.

The invention determines the fatigue life of a rubber material exactly, and easier, cheaper and more accurate results are obtained as compared to the other machines in the state of the art. In addition, the fatigue lives of the rubber types having different structures may be compared by the machine of the invention. The fatigue life of a rubber material is determined upon the tests and experiments carried out by the machine of the invention. After the fatigue life is determined exactly, a manufacturing process of a prototype and part is performed for the rubber material.

Description of Figures

Figure 1 is a representative front view of a machine of the invention, which is located on a chassis as six pieces in one embodiment.

Figure 2 is a large-scaled representative front view of a part used to determine the lifetime of an elastic material in the machine of the invention.

Figure 3 is a large-scaled representative view of a moment during which an elastic material located between the upper shaft and lower shaft of the machine according to the invention is unbalanced, that is under the pressure and draft pressures.

Figure 4 is a representative side view of a machine of the invention, which is located on a chassis as six pieces in one embodiment.

Figure 5 is a representative top view of a machine of the invention, which is located on a chassis as six pieces in one embodiment.

Figure 6 is a representative isometric view of a machine of the invention, which is located on a chassis as six pieces in one embodiment.

Description of the References in the Figures In order to provide a better understanding of the invention, the numerals in the figures are provided below:

1. Machine

1.1. Upper Shaft

1.2. Lower Shaft

1.3. Drive Shaft

1.4. Drive member

1.5. Bending member

1.6. Pushing member

1.7. Detector

EM. Elastic Material

§. Chassis

TQ. Carrying rod

Detailed Description of the Invention:

The machine (1) of the invention comprises an upper shaft (1.1) applying a stress (or a pressure) by being bent at the predetermined values of an angle to an elastic material (EM), a lower shaft (1.2) on which said elastic material (EM) is positioned and which rotates the elastic material (EM) around its own axis (a symmetry axis), a drive shaft (1.3) mounted to said lower shaft (1.2), a drive member (1.4) which rotates the drive shaft (1.3) at a predetermined rotation speed, a bending member (1.5) which enables the upper shaft (1.1) to apply a stress to the elastic material (EM) by bending the upper shaft (1.1) by a predetermined angle, a pushing member (1.6) which enables said bending member (1.5) to angle the upper shaft (1.1), and a detector (1.7) for measuring a force value formed by the elastic material (EM) in the opposite direction to the force applied thereto, for determining the fatigue life of the elastic materials (EM).

The machine (1) also comprises a cycle counter (not shown and numbered in the figures) which measures the number of cycles (or revolutions) of the drive shaft (1.3) and a rod (not shown and numbered in the figures) which is located anywhere on the drive shaft (1.3) to count the cycle. Said counting process is performed using said part or rod passing by the cycle counter. Every passing process constitutes one full cycle.

The upper shaft (1.1) and the lower shaft (1.2) are preferably made of a metal, but it is not limited thereto in practice. The elastic material (EM), the lifetime of which will be determined, is positioned between the upper shaft (1.1) and the lower shaft (1.2). The upper shaft (1.1) and the lower shaft (1.2) are in contact with preferably cylindrical lower and upper pieces of the elastic material (EM). Upon positioning of the elastic material (EM) between the upper shaft (1.1) and the lower shaft (1.2), the elastic material (EM) is rotated around the symmetry axis (that is, the axis passing through the center point of the material) of the elastic material (EM). The elastic material (EM) is rotated by the drive shaft (1.3) moving rotationally via the drive member (1.4) which allows rotation.

The fatigue life of the cylindrical elastic material (EM) which is chosen in any form in the invention is determined with the machine (1) of the invention. In a preferred embodiment of the invention, the elastic material (EM) (or an elastomeric material) is rubber, but it is not limited thereto in practice.

In the invention, the detector (1.7) is a force sensor and measures the force value formed by the elastic material (EM) under load.

In the invention, the fatigue life of more than one elastic materials (EM) is determined by more than one machine (1) simultaneously. More than one machines (1) are mounted on the chassis (§) and operated. In the invention, preferably six machines (1) are mounted on the chassis (§), but it is not limited thereto in practice. Thus, the fatigue life of 6 elastic materials (EM) is determined simultaneously. In said embodiment, all of the upper shafts (1.1) are brought to the bending mode at the same time. At the same time, the drive shaft (1.3) to which the lower shaft (1.2) is connected and the lower shaft (1.2) are rotated around a fixed axis at a predetermined fixed speed by a belt and pulley system to which the drive member is connected and the drive member (1.4).

When a point is marked on the elastic material (EM), if this point completes one full cycle around the symmetry axis of the elastic material (EM), that is, if this point constantly moves in a rotational movement, said point switches to a draft mode when it reaches the side of the elastic material (EM) to which no pressure is applied, to a neutral mode when it is in the middle, and to a pressure mode when it reaches the side there of to which a pressure is applied. Thus, a stress (or stain) variation is created on the material. A dynamic forcing state is created on the material during both draft and pressure modes. Said point of the elastic material (EM) is exposed to a cyclic stress and pressure. Thus, the behavior of the elastic material (EM) against the cyclic stress and pressure during the fatigue tests will be characterized. The upper shaft (1.1) is bent at a fixed angle and applies the same stress to the elastic material (EM) during the measurement process. During said measurement process, the difference between the draft stress and the pressure stress equals to the stress amplitude of the elastic material (EM). For example, in case that a draft of 120% and a pressure of 70% are created on the elastic material (EM), a stress amplitude of 190% is formed with a predetermined constant rotation speed. Cracks (or deformations) are formed on the material over time due to the pressure applied, and the material begins to be torn upon formation of the cracks. When the elastic material (EM) is forced to bent under a stress, the material tends to be flat, that is tends to return to a balanced state. Then, the elastic material (EM) starts to exhibit resistance. Thus, the material forms a resistance against bending. A force is created at a level of the resistance of the material against bending. When the upper shaft (1.1) is bent at a predetermined angle, the detector (1.7) is also bent at the same angle and in the same direction towards which the upper shaft (1.1) is bent. Then, a force value will be read from the detector (1.7). The elastic material (EM) forms a force in an opposite direction to the movement. At the same time, a force value is read from the detector (1.7), that is, the force sensors. When a rotation is started in the same direction along all axes, a same number of rotation and the same force values are measured. The force reaction applied by the elastic material (EM) is reduced as the elastic material (EM) starts to wear or tear over time. Thus, the resistance force is reduced. This is known from the force value read from the detectors (1.7). In one embodiment of the invention, the lifetime of the elastic material (EM) is completed when there is a reduction of 30% in the amplitude read at a specified bending angle. For example, when the elastic material (EM) completes a full cycle of 1.000.000 and there is a reduction of 30% in the amplitude at the end of this, it is understood that the lifetime of the elastic material (EM) is a full cycle of 1.000.000. The measurements are repeated for the same material in the bending modes at varying angles. When a break value is obtained assuming that it is pushed by an angle of 15° by the pushing member (1.6), this value is maximum. As the angle increases, the stress applied to the elastic material (EM) is increased (See Graph-1). Accordingly, the lifetime is reduced. At least a number of points are required to create a CF (Constant Fatigue) curve. The curve rendered constant using a curve fitting function relative to said points. That is, the points are found by interpolation. For example, in case of 15°, 30° , 45° , a stress corresponding to 18° is found, as a function is created by combining the points.

Graph -1 : Graph for the Elastic Material (EM)- Stress Life

Installation of the machine (1) according to the invention is rather simple. The measurement is performed practically. The desired displacement is obtained with the machine (1) without a super-advanced technology. The strain on the elastic material (EM) rotated around its own axis by bending the upper shaft (1.1) up to a predetermined distance by a simple pushing member (1.6), for example a piston, creating a strain on the material, and using a drive member (1.4) for the machine (1) behind the chassis (or panel) and hence, the lifetime of the elastic material (EM) are known.

In the invention, the life strength is modelled with the values of said machine (1); a function is obtained from the Wohler curve; and a material strain of that angle for any angle entered in the function is obtained. Thus, the life strength of the materials with the same material structure but different geometries may also be estimated with the invention.

In the invention, a maximum stress (Smax) and a minimum stress (Smin) are created quickly at different values from each other on the rubber by the machine (1) of the invention, in order to accurately determine the fatigue characteristic, hence the life, of the rubber material. This is done under a varying load. The system operates according to the principle of rotational deviation. A standardized rubber block is used as a coupling between two shafts. These two shafts are angularly connected at a certain angle. Couplings are used to connect two shafts. The shafts and pivots vibrate when they are not connected in a fully adjusted manner. In order to minimize that vibration, two devices are necessarily connected via couplings at a certain angle. The rubber is unilaterally actuated. At a certain moment, a predetermined part of one end of the rubber is tensioned fully, while a predetermined part of the other end thereof is compressed. Thus, when it completes half of the cycle, the part that was in compression in the previous state switches to tension in the second state. As the geometry of the material is standard, the stresses and controlled elongations depending on the angle are also known. Reducing the load on the rubber part by a certain percentage is also a criterion. When the maximum force on the rubber decreases by a predetermined percentage, it is understood that the lifetime of this part is completed. Consequently, the shafts are bent at different angles relative to each other in order to obtain a maximum and minimum stress, and this process is carrier out very quickly. By measuring the forces at the controlled angles and displacements, the lifetime of the rubber parts may be determined periodically. As the conditions are very controlled in terms of both displacement and rotation, different types of rubbers may be compared with each other by the lifetime determining machine (1) of the invention.

Industrial Applicability of the Invention:

The invention is especially determined the fatigue characteristic of the rubber materials used in the automobile industry and is applied industrially.

The invention is not limited to the foregoing exemplary embodiments, and one person skilled in the art may easily reveal the different embodiments of the invention. These should be considered within the scope of protection of the invention claimed in the claims.

Claims

CLAIMS A machine (1) for determining the fatigue life of the elastic materials (EM), characterized in that it comprises: an upper shaft (1.1) applying a stress (or a pressure) by being bent at the predetermined values of an angle to an elastic material (EM), a lower shaft (1.2) on which said elastic material (EM) is positioned and which rotates the elastic material (EM) around its own axis (a symmetry axis), a drive shaft (1.3) mounted to said lower shaft (1.2), a drive member (1.4) which rotates the drive shaft (1.3) at a predetermined rotation speed, a bending member (1.5) which enables the upper shaft (1.1) to apply a stress to the elastic material (EM) by bending the upper shaft (1.1) by a predetermined angle, a pushing member (1.6) which enables said bending member (1.5) to angle the upper shaft (1.1), and a detector (1.7) for measuring a force value formed by the elastic material (EM) in the opposite direction to the force applied thereto. A machine (1) as claimed in claim 1, characterized in that it comprises an upper shaft (1.1) and a lower shaft (1.2), which are made of a metal.

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