1、 Brief intbaruction of dynamic hardness test system shd-1000
Hardness is often used to characterize the ability of materials to resist indentation deformation, to reflect the yield strength, strain hardening ability or the strength of bond between atoms. The traditional hardness measurement technology effectively reflects the mechanical properties of materials in the quasi-static process, but the existing research shows that the plastic deformation behavior of most materials has strain rate correlation, and the yield stress of most metals will increase under the condition of high strain rate;
The fracture toughness and fracture strength of ceramics will also be improved due to the strain rate effect. Therefore, the static hardness can not reflect the high strain rate behavior of materials in high-speed cutting or high-speed collision. Dynamic indentation is formed on the surface of the specimen by the stress pulse acting on the rigid indenter contacting with the specimen, and then the dynamic indentation hardness of the material is measured, which is called dynamic hardness for short.
The dynamic hardness reflects the ability of the material to resist the dynamic pressing deformation of the indenter, and its strain rate reaches 10 ~ 104 / s. at the same time, the dynamic hardness test is quick and convenient, and the sample is not damaged. Therefore, dynamic hardness is an important parameter which can reflect the high strain rate behavior of materials under complex three-dimensional stress conditions, and it is expected to become a new method to evaluate the dynamic properties of materials. The dynamic hardness test system is based on the traditional SHPB device. According to the principle of single stress pulse loading, a new dynamic hardness test system is established. Its structure is shown in Figure 1. The system consists of a single stress pulse generator, a waveform shaper, a pressure head, a signal acquisition device and a data processing device.
2、 Working principle of dynamic hardness test system shd-1000 The core of the whole system is a single stress pulse generator. It is composed of bullet, incident bar and flange, sleeve and mass action block at its end. When the bullet strikes the flange, the compression wave propagates to the incident bar and the sleeve at the same time. Because the sleeve and the mass action block are close to each other, the compression wave propagated along the sleeve reflects into a compression wave at the boundary between the sleeve and the mass action block and propagates along the sleeve to the end face of the flange. At the end face of the flange, the reflection is a tensile wave propagating towards the pressure head. The bullet and the sleeve have the same acoustic resistance and length, so the compression wave propagating to the left of the sleeve and the stretch wave reflected from the left free end of the bullet reach the flange at the same time, and the stretch wave propagates in the direction of the compression wave to the indenter. The compression pulse is reflected as a tensile wave at the end of the indenter, and it is absorbed by the sleeve and the mass action block when it propagates to the left of the flange and sleeve interface, instead of being reflected as a compression wave entering the incident bar again, resulting in the / momentum trap effect. After that, the right traveling wave of the incident bar only has a tensile wave, which ensures that the sample is only loaded by a compression pulse. Fig. 2 (a) and (b) are the theoretical waveforms of the stress wave propagation in the incident bar and the measured waveforms collected by the strain gauge respectively. It can be seen that the compression wave propagates only once towards the indenter in the incident bar. In order to adjust the loading rate of the loading stress pulse, filter out the high frequency part of the incident stress wave, improve the experimental accuracy and protect the diamond indenter, it is necessary to shape the loading pulse. The dynamic hardness test system uses a special Vickers diamond indenter, which is connected to the end of the incident bar by screws and other devices. During the test, there is no prestressed contact between the indenter and one end of the sample, and the other end of the sample is in contact with the piezoelectric sensor. The output signal of the piezoelectric sensor is amplified by the charge amplifier and then input into the computer and recorded in real time. The data processing software of Hopkinson pull bar can automatically identify the jumping point and the ending point of the transmitted and reflected waves, and can also identify manually. At the same time, it can test the square sample, and calculate the impact stress-strain, strain energy, particle velocity, reflection energy, transmission energy and other data of the sample. It is simple to operate and convenient to use. According to the first-class level of the current industry. Hopkinson multi-functional pull bar equipment mainly consists of air storage device, launch and control control system, bar system and bullet, measurement and analysis system, center support component, combined foundation guide rail, active confining pressure part, single loading device, buffer device and auxiliary equipment. Hopkinson multi-functional pull and pull equipment is a set of special test equipment based on a unified high-precision benchmark.
The special parts which are mainly different from other equipment are described as follows:
Launching system: it is composed of air chamber, launching body, control module, piston, connecting flange, quick change variable diameter gun tube, support seat, anti back seat bracket, etc.
Rod diameter: Φ 10, Φ 8 Rod system and bullet: the material is 18Ni, spring steel, titanium and other high-strength steel; the metal materials are overheated, and the perpendicularity of all bar end faces can be within 0.02, and the bar diameter and end face roughness can be above Ra0.8.
3. dynamic hardness testing system SHD-1000 data acquisition system
1. Equipment function intbaruction and main technical indexes: Alt1000 ultra dynamic data acquisition system is specially used for the test and analysis of hobkinson bar experiment. The highest transient sampling rate of the system is 40MHz, each channel is independent of a / D analog-to-digital converter, and the external strain conditioner completes the stress-strain test and analysis of 1 / 4 bridge, half bridge and full bridge states. The system has the functions of real-time acquisition, real-time display, real-time storage and real-time analysis of the measured signal, automatic test control and data waveform analysis and processing. 4、 Brief intbaruction of shd-1000 software for dynamic hardness testing system
5、 Test results:
Dynamic hardness test method static Vickers hardness reflects the pressure on the surface area of the unit indentation, and its physical meaning is clear. Therefore, according to the static Vickers test principle and its measurement standard, according to the dynamic stress and strain, as well as the Vickers indentation size, the dynamic Vickers hardness calculation results can be obtained.
Dynamic Hardness Result |
