RU2110051C1 - Method of overload pulse formation at impact tests - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: platform with object under test positioned loosely on it is accelerated till it collides with braking device, and object is braked by second braking device. The latter is positioned between object and platform. Method enable increase in amplitude and rate of pulse rise due to installation of object relative to second braking device with clearance to be selected from relation δ = K•v $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ •v $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ /2g•(n₂-n₁)²/n₁•n₂,, where δ is clearance; v₀ is platform acceleration speed; g is free fall acceleration; n₁ is overload on platform; n₂ is overload of object under test; K is empirical coefficient which depends on correlation of masses of object under test and platform and on overload pulse forms on object under test and platform. EFFECT: enhanced formation of overload pulse. 1 dwg

Description

 The invention relates to the field of testing equipment, in particular to testing objects for impact loads.

 When testing objects for impact loads, the object is exposed to an overload pulse with predetermined characteristics - the steepness of the leading edge and amplitude.

 One of the challenges in the field of test technology is to increase the characteristics of the overload pulse.

 Closest to the invention is a method of generating an overload pulse used in a bench for testing products for shock loads of a rectangular shape (ed. St. N 445870 03/30/71, ed. Stepanov VD, Bulletin N 37, 1974). The method consists in the fact that the test object is fixed on a table connected to the platform of the shock stand by means of a brake device placed between the table and the platform (hereinafter referred to as the internal brake device), the platform is accelerated and then braked by a collision with the brake device (hereinafter text - external brake device) of the shock stand. When the platform collides with an external braking device, the load is affected by the load during the active stage of the impact, which is transmitted through the platform structure and the internal brake device to the table with the object, as a result of which the table with the test object begins to brake and the impulse forms on it overload. At the same time, in the initial stage of the impact, until the load transmitted through the internal braking device reaches the value that determines the beginning of its working stroke, the table with the test object will experience the same overload as the platform. Over time, the load transmitted through the internal brake device reaches a value that determines the beginning of its working stroke, and there is a movement of the table with the test object relative to the platform, as a result of which the overload acting on the table undergoes changes (decreases) compared with the overload acting to the platform.

 When using known methods for generating an overload pulse, to increase the characteristics of the pulse, it would be necessary to increase the resistance force of both internal and external braking devices.

 The disadvantage of this method (see ed. St. N 445870) is the need to create an overload pulse on the platform with higher overload characteristics (the steepness of the leading edge and the amplitude of the overload on the platform should be greater than the corresponding characteristics compared to the overload pulse formed on the table with the test object) pulse), which requires the use of platforms with increased strength, the use of external braking devices with high braking forces, an increase in the load on the braking devices and foundations stand the shock. However, in some cases, for example, when testing objects of large dimensions and mass, when testing for the effects of high level overloads and with a large steepness of the leading edge, due to the limited capabilities of shock stands (restrictions on the maximum platform weight, on the permissible load on the shock foundation stand and external braking device, etc.), it is not possible to provide sufficient platform strength and the required magnitude and steepness of the leading edge of the force pulse generated by the external braking device, which ichivaet opportunity to known methods in relation to the test load. In addition, during the formation of an overload pulse with a large steepness of the leading edge, the latter appears to be distorted by resonant vibrations arising in the platform structure under the influence of its sharp impact on the external braking device and transmitted to the table with the test object in the initial stage of impact, while the internal braking device operates as a rigid communication.

 The aim of the invention is to increase the characteristics of the overload pulse at the test object, namely an increase in the amplitude and steepness of the leading edge of the pulse, without increasing the loads on the elements of the shock stand, as well as improving the accuracy of reproduction of the leading edge of the overload pulse.

где
δ - зазор;
V₀ - скорость разгона платформы;
g - ускорение силы тяжести;
n₂ - перегрузка на объекте испытаний;
n₁ - перегрузка на платформе;
K - коэффициент, определяемый экспериментально, в зависимости от соотношения масс объекта испытаний со столом и массы платформы и от формы импульсов перегрузок на объекте испытаний и платформе, а n₁ ≠ n₂.The goal is achieved by the fact that in the known test method, the start of braking of the table with the test object is shifted relative to the start of braking of the platform by setting a gap between the table and the internal brake device, the gap being selected from the ratio

Where
δ is the gap;
V ₀ is the acceleration speed of the platform;
g is the acceleration of gravity;
n ₂ - overload at the test object;
n ₁ - overload on the platform;
K is the coefficient determined experimentally, depending on the ratio of the masses of the test object with the table and the mass of the platform and on the shape of the overload pulses on the test object and platform, and n ₁ ≠ n ₂ .

 If there is a gap between the table and the internal braking device during braking of the platform, the table is displaced relative to the platform, since the speed of the platform is suppressed by the external braking device, and the speed of the table, which does not have a rigid connection with the platform, remains constant.

 Having shifted relative to the platform by the amount of the gap and having acquired a certain speed relative to the platform during the displacement, the table hits the internal braking device and is braked by it, as a result of which an overload pulse is formed on the table with the test object.

 The fundamental difference between the proposed method of generating an overload pulse from the known methods is that the braking of the object does not begin simultaneously with the beginning of the braking of the platform, but after a certain period of time during which the table with the object moves within the gap, thereby eliminating the influence of the front slope of the front and amplitude of the load acting on the platform during this period of time on the characteristic of the generated pulse, the values of which by The actual adjustment of the gap and power characteristics of the internal braking device can be assigned regardless of the values of the characteristics of the overload pulse acting on the platform, i.e., they can be not only less, but also more of them. To increase the characteristics of the overload pulse, it is enough to increase the gap and the resistance force of the internal brake device, and the resistance force of the external brake device can not be changed. Thus, it becomes possible to increase the characteristics of the overload pulse at the test object without increasing the characteristics of the overload pulse acting on the platform and increase the loads on the brake device and the foundation of the shock stand, which will expand the operational characteristics of the shock stand. Improving the accuracy of reproduction of the leading edge of the pulse is ensured by the fact that, as a result of eliminating the connection between the table and the platform in the initial stage of impact of the platform by setting a gap, the resonant vibrations arising in the platform structure under the influence of its impact on the external braking device are not transmitted to the table, and by the time the contact is established (the beginning of table braking), the leading edge of the generated overload pulse is damped and does not distort.

 The drawing shows a diagram of a device on which the proposed method can be implemented.

 The test object 1 is fixed on the table 2 of the platform 3 of the shock stand 4. Between the platform 3 and the table 2 there is an internal brake device 5. The table is connected by a rigid connection 6 to the platform 3 so that a gap δ is formed between the table 2 and the internal brake device 5 . . Platform 3 is driven to a predetermined speed and hits the external braking device 7. When a collision is made, the rigid connection 6 is destroyed, table 2 acquires freedom of movement, and platform 3 is braked. Table 2 is shifted towards the platform 3, hits the internal brake device 5 and is exposed to an overload pulse. The steepness of the leading edge of the pulse and its amplitude will be determined by the value of the gap δ between the table 2 and the internal brake device 5 and the power characteristic of the internal brake device 5.

 Using the proposed method for generating an overload pulse during impact testing of objects provides the following advantages compared to existing methods: the ability to increase the characteristics of the overload pulse at the test object without increasing the loads on the elements of the shock stand and increasing the accuracy of reproduction of the leading edge of the overload pulse, which will significantly expand the range of characteristics of shock pulses created on existing drum stands. An experimental verification of the proposed method of generating an overload pulse, carried out on the model, confirmed the effectiveness of the method.

Claims (1)

The method of generating an overload impulse during shock tests, namely, that the platform with the test object, which is mounted with the possibility of moving relative to the platform when the latter is braked, is accelerated to the collision with the braking device and the test object is braked by the second braking device, which is installed between the test object and the platform characterized in that, in order to increase the achievable amplitude and steepness of the leading edge of the pulse, the test object is set relative torogo braking device with a gap, which is selected from the relation

where δ is the gap;
V ₀ is the acceleration speed of the platform;
g is the acceleration of gravity;
n ₁ - overload on the platform;
n ₂ - overload at the test object;
K is an empirical coefficient depending on the mass ratio of the test object and platform and on the shape of the overload pulses on the test object and platform.