An all-electric instrumented tensile impact fatigue test system

Abstract

The application provides a full-electric instrumented tensile impact fatigue test system, and mainly solves the problems of stress wave pulse transmission in a rod back and forth, non-repeated cyclic loading test and automatic test. The application uses a Hopkinson rod system, a stress wave riveting gun module, a screw drive and a comprehensive detection and controller to realize single repeated impact loading of a test piece, control of the emission and recovery of a projectile body, and closed-loop control of loading force. The application realizes the single loading impact fatigue function of the test piece by energy absorption and a stopper and a screw drive, and realizes instrumented and full-automatic impact tensile fatigue test.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material fatigue performance test experiment, and mainly relates to a full-electricity measurement and control instrumented tensile impact fatigue experiment system. BACKGROUND

[0002] Various equipments and engineering structures often bear repeated impact loading (also known as impact fatigue) in use, which means that the speed of each loading is high, and the deformation rate of the material is high, that is, the impact speed can reach dozens of meters per second, and the strain rate of the material can reach about 10 2 / s order. Under high loading rate, the equipments and engineering structures usually appear crack initiation, cracking and expansion under impact tension, and develop to final failure under high strain rate repeated tension, so the impact repeated tension experiment loading device, that is, the impact fatigue experiment system, is an essential technical means for designing structures and evaluating material performance.

[0003] The prior art discloses a method for realizing high-speed loading of a riveted joint (cylindrical material), which is usually called a "stress wave riveting gun". Referring to Figure 1 , the document: Cao Zengqiang, Tao Hua, She Gongfan, Li Zhiyao, Sheng Xi, Stress Wave Riveting of Large Diameter Riveted Joints, New Technology - New Technology - New Equipment, 1996.2, 27-28 [J]. The device includes a transformer 1, a rectifier silicon stack 2, a capacitor group 3, a vacuum switch 4, a buffer element 5, a primary coil 6, a secondary coil 7, a stress wave modulator 8, and a rivet 9. During the experiment, when impact compression load is applied to the rivet 9, the transformer 1 is first turned on to charge the capacitor group 3, and when the voltage reaches a predetermined value, the vacuum switch 4 is turned on. When the transient large current passes through the primary coil 6, magnetic induction and eddy current are generated in the secondary coil 7, forming Lorentz force which in turn acts on the primary coil 6, so that the secondary coil 7 generates enhanced stress pulse to the stress wave modulator 8, which acts on the rivet 9 and deforms, realizing impact loading of the rivet 9.

[0004] The prior art discloses an electromagnetic Hopkinson pressure bar loading method. Referring to Figure 2The device includes a compression specimen 10, a compression incident rod 11, a compression transmission rod 12, a capacitor group 13, an effective coil 14, an induction coil 15, and a stress wave amplifier 16. The method is based on the traditional Hopkinson pressure bar principle, and the impact rod loading is changed into a "stress wave riveting gun" loading. During the experiment, the stress wave amplifier 16 generates an enhanced stress pulse along the compression incident rod 11 to load the compression specimen 10. Strain gauges are attached to the compression incident rod 11 and the compression transmission rod 12 to obtain the impact loading history signal.

[0005] A pneumatic control repeated impact compression loading device system is disclosed in the prior art, which can realize repeated impact compression of a cylindrical specimen. Referring to Figure 3 The device includes a high-pressure air cylinder 17, an impact rod 18, a variable-diameter rod 19, a compression specimen 20, a first strain gauge 21, a compression incident rod 22, a second strain gauge 23, an energy absorption rod 24, and a pneumatic stopper 25. Figure 3 The schematic diagram below represents the working order of each part when the impact rod moves once. Blue represents low pressure, magenta represents medium pressure, and red represents high pressure. During the experiment, when the air pressure enters the high-pressure air cylinder 17, it pushes the impact rod 18 to hit the variable-diameter rod 19, generating an impact signal to the compression specimen 20. The first strain gauge 21 and the second strain gauge 23 collect data at the same time as the pneumatic control signal. The high-pressure air cylinder 17 and the pneumatic stopper 25 are designed in different variable-diameter forms to realize limiting and single impact single loading of the specimen. This system can realize repeated impact loading by using electromagnetic switch valves and controllers.

[0006] Among the above three test methods, Figure 1 This "stress wave riveting gun" can realize impact compression of rivets or specimens, but it cannot display the impact wave configuration, cannot quantify the impact force, and cannot be directly used as an experimental device for testing the dynamic experimental performance of materials. Figure 2 This Hopkinson bar electromagnetic loading system basically meets the requirements of a single impact compression loading experimental device, but it belongs to the impact compression mode and does not constitute a repeated cycle loading. Figure 3The cyclic impact compression loading experimental device is for repeated compression impact loading of the sample, in the impact loading, stress wave pulses are transmitted back and forth in the rod, due to the material dispersion and geometric characteristics of the loading rod, the repeated back and forth of the stress wave will be continuously attenuated, and the sample must be waited until the attenuation of the repeatedly transmitted stress wave ends before the next loading, therefore, the secondary loading of the subsequent reflected stress wave pulses is also considered to achieve the one-time impact loading on the sample.

[0007] In summary, in order to solve the problem of repeated impact loading in the tensile mode, the problem of multiple loadings on the sample under impact loading, and the problem of non-automation of the instrument, an instrumented automatic experimental system needs to be constructed. SUMMARY

[0008] In order to overcome the shortcomings of the prior art, the present application provides a full-electric measurement and control instrumented tensile impact fatigue experimental system, which realizes the automation and instrumentality of the tensile impact fatigue system. The Hopkinson rod system, stress wave riveting gun module, screw drive, comprehensive detection and controller are used to realize single repeated impact loading on the test piece, solve the problem of repeated impact loading in the tensile mode, the problem of multiple loadings on the sample under impact loading, and the problem of non-automation of the instrument.

[0009] A full-electric measurement and control instrumented tensile impact fatigue experimental system includes a pulse emission module, a sample loading module, a screw drive 41 and a metal screw rod; the pulse emission module includes a stress wave riveting gun module and a pulse emission control circuit; the sample loading module is a Hopkinson compression rod; the sample loading module includes a tensile incident rod 48, a tensile transmission rod 42, a dumbbell-shaped sample 46 and a damping module; the damping module includes an energy absorption and stopper 38 and a damping blocker 39; the screw drive 41 includes a lead screw drive motor and an LVDT linear displacement differential transformer 40;

[0010] The stress wave riveting gun module comprises a buffer element 32, a primary coil 33, a secondary coil 34 and a stress wave modulator 35; the buffer element 32, the primary coil 33 and the secondary coil 34 are all hollow cylinders; the stress wave modulator 35 is a cone; the radius of the bottom surface of the stress wave modulator 35 is the same as that of the bottom surface of the secondary coil 34; the stress wave modulator 35 is provided with a through hole in the axial direction; the radius of the through hole is the same as that of the inner ring of the secondary coil 34; the primary coil 33, the secondary coil 34 and the stress wave modulator 35 are sequentially arranged based on one bottom surface of the buffer element 32; after the buffer element 32, the primary coil 33, the secondary coil 34 and the stress wave modulator 35 are combined, they are coaxial; the through hole, the inner ring of the buffer element 32, the inner ring of the primary coil 33 and the inner ring of the secondary coil 34 are connected to form a through hole; the primary coil 33 is connected with a pulse emission control circuit;

[0011] The pulse emission control circuit comprises a transformer 26, a rectifier silicon stack 27, a charging voltage detector 28, a vacuum switch 29, a voltage-time switch 30 and a capacitor group 31; one end of the vacuum switch 29 is connected with the primary coil 33; the other end of the vacuum switch 29 is connected with the charging voltage detector 28; the other end of the charging voltage detector 28 is respectively connected with one end of the rectifier silicon stack 27 and one end of the capacitor group 31; the other end of the rectifier silicon stack 27 is connected with the transformer 26; the other end of the transformer 26 is connected with the voltage-time switch 30; the other end of the capacitor group 31 is respectively connected with the voltage-time switch 30 and the primary coil 33;

[0012] The stretching incident rod 48 is horizontally arranged in the through hole; the flange 36 is arranged on the end surface of the stretching incident rod 48 close to the vertex of the stress wave modulator 35; the damping stopper 39 is a cylinder; the damping stopper 39 is fixed on the experimental frame; the energy absorption and limiting device 38 is arranged in the damping stopper 39; the energy absorption and limiting device 38 is a metal rod; a gap is arranged between the flange 36 and the energy absorption and limiting device 38; the length of the gap is △;

[0013] One end of the stretching transmission rod 42 is connected with the dumbbell-shaped sample 46; the other end of the stretching transmission rod 42 is fixedly connected with one end of a metal screw rod; the other end of the metal screw rod is fixedly connected with the lead screw driver 41; the LVDT linear displacement differential transformer 40 and the lead screw driver 41 are both fixed on the experimental frame; after the LVDT linear displacement differential transformer 40, the lead screw driver 41 and the sample loading module are installed, the stretching transmission rod 42, the dumbbell-shaped sample 46, the stretching incident rod 48, the metal screw rod and the energy absorption and limiting device 38 are collinear.

[0014] Further, the damping stopper 39 is provided with threads; the energy absorption and limiting device 38 is fixedly connected with the damping stopper 39 through the threads; after the energy absorption and limiting device 38 is arranged in the damping stopper 39, the damping stopper 39 is filled with energy absorption materials; and the energy absorption and limiting device 38 is coaxial.

[0015] Further, the end face of the tensile incident rod 48 connected with the dumbbell-shaped sample 46 is provided with an incident rod trapezoidal groove 47; the incident rod trapezoidal groove 47 is a quadrangular pyramid; the bottom face with the smallest area of the incident rod trapezoidal groove 47 is the end face of the tensile incident rod 48; the bottom face with the smallest area and one side face of the incident rod trapezoidal groove 47 are open; the dumbbell-shaped sample 46 is arranged in the incident rod trapezoidal groove 47; one end of the dumbbell-shaped sample 46 is arranged in the incident rod trapezoidal groove 47; the other end of the dumbbell-shaped sample 46 is arranged in the transmission rod trapezoidal groove 45 of the tensile transmission rod 42; the transmission rod trapezoidal groove 45 is a quadrangular pyramid; the bottom face with the smallest area of the transmission rod trapezoidal groove 45 is the end face of the tensile transmission rod 42; the bottom face with the smallest area and one side face of the transmission rod trapezoidal groove 45 are open; after the two end heads of the dumbbell-shaped sample 46 are respectively arranged in the transmission rod trapezoidal groove 45 and the incident rod trapezoidal groove 47, a sample gap is arranged between the bottom face with the largest area of the transmission rod trapezoidal groove 45 and the end head of the dumbbell-shaped sample 46, and a sample gap is arranged between the bottom face with the largest area of the incident rod trapezoidal groove 47 and the end head of the dumbbell-shaped sample 46.

[0016] Further, the length of the energy absorption and limiting device 38 is greater than the wavelength of the stress wave generated by the system.

[0017] Further, the length of the gap is calculated in advance according to the tensile shock wave form.

[0018] Further, the gap photoelectric detector 37 is arranged directly above the gap.

[0019] Further, the tensile transmission rod 42 is provided with a first strain gauge 43; and the tensile incident rod 48 is provided with a second strain gauge 49.

[0020] Further, the all-electric instrumented tensile impact fatigue test system comprises an automatic control module and a data acquisition module; the automatic control module comprises a comprehensive detection and controller 50 and a peak detector 53; the comprehensive detection and controller 50 is a computer; the comprehensive detection and controller 50 is connected with a lead screw actuator 41, a voltage-time switch 30, a gap photoelectric detector 37, a charging voltage detector 28 and a vacuum switch 29 respectively; the peak detector 53 is connected with an LVDT linear displacement differential transformer 40; the automatic control module is used for controlling the test system, and the transmission rod and the sample are reset after being loaded by an electrical signal, so that single loading of the sample is ensured; the data acquisition module comprises an ultra-dynamic strain gauge 54, the peak detector 53, a voltage comparator 52 and a PID regulator 51; a first strain gauge 43 is connected with the ultra-dynamic strain gauge 54; a second strain gauge 49 is connected with the ultra-dynamic strain gauge 54; the ultra-dynamic strain gauge 54, the peak detector 53, the voltage comparator 52 and the PID regulator 51 are all connected with the comprehensive detection and controller 50; data acquisition is used for collecting impact force waveform, amplitude, displacement value, impact frequency and data in real time.

[0021] Further, the rubber sleeve 44 is arranged on the tensile incident rod 48, and is used for preventing the sample from falling.

[0022] Further, the primary coil 33 and the secondary coil 34 are both wire windings; the stress wave modulator 35 is made of steel; the buffer element 32 is made of a high polymer material and steel, and the high polymer material is coated in the inside of the steel; the energy absorption material is rubber clay or lead.

[0023] Further, the energy absorption and stopper 38, the tensile transmission rod 42 and the tensile incident rod 48 are made of titanium alloy or aluminum alloy.

[0024] The beneficial effects of the present application are as follows:

[0025] 1) The present application provides an all-electric driving, detecting and controlling high-strain-rate impact tensile fatigue test system, and realizes instrumented and full automation of the impact tensile fatigue test;

[0026] 2) The present application adopts a hooking type tensile sample, the sample is connected with the end of the slotted loading rod, and realizes single loading impact fatigue function of the sample by the energy absorption and stopper 38 and the lead screw actuator 41;

[0027] 3) The present application designs a closed-loop control of impact fatigue, including closed-loop control of impact force and displacement, and realizes amplitude stability of the impact force and displacement in the impact fatigue process;

[0028] 4) The present application uses a large current electromagnetic "stress wave riveting gun" to generate a half-sine impact tensile pulse, with high impact energy and large impact force. By detecting the electrical signals of force and displacement during impact fatigue, the sample loading can be displayed and controlled in real time, achieving fast response, high synchronization and good stability in electrical measurement and control. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a large-diameter riveting stress wave riveting schematic diagram proposed in background reference 1;

[0030] Figure 2 is a Hopkinson bar electromagnetic loading system design and experimental schematic diagram in background reference 2;

[0031] Figure 3 is a cyclic impact compression loading experimental system schematic diagram in background reference 3;

[0032] Figure 4 is a fully instrumented tensile impact fatigue experimental system schematic diagram;

[0033] Figure 5 is a schematic diagram of the transmission bar trapezoidal groove and the incident bar trapezoidal groove;

[0034] BRIEF DESCRIPTION OF DRAWINGS: 1 - transformer; 2 - rectifier silicon stack; 3 - capacitor group; 4 - vacuum switch; 5 - buffer element; 6 - primary coil; 7 - secondary coil; 8 - stress wave modulator; 9 - rivet; 10 - compression sample; 11 - compression incident bar; 12 - compression transmission bar; 13 - capacitor group; 14 - effective coil; 15 - induction coil; 16 - stress wave amplifier; 17 - high-pressure air cylinder; 18 - impact bar; 19 - variable-diameter bar; 20 - compression sample; 21 - No. 1 strain gauge; 22 - compression incident bar; 23 - No. 2 strain gauge; 24 - energy absorption bar; 25 - pneumatic stopper; 26 - transformer; 27 - rectifier silicon stack; 28 - charging voltage detector; 29 - vacuum switch; 30 - voltage-time switch; 31 - capacitor group; 32 - buffer element; 33 - primary coil; 34 - secondary coil; 35 - stress wave modulator; 36 - flange; 37 - gap photodetector; 38 - energy absorption and stopper; 39 - damping stopper; 40 - LVDT linear displacement differential transformer; 41 - lead screw driver; 42 - tensile transmission bar; 43 - No. 1 strain gauge; 44 - rubber sleeve; 45 - transmission bar trapezoidal groove; 46 - dumbbell-shaped sample; 47 - incident bar trapezoidal groove; 48 - tensile incident bar; 49 - No. 2 strain gauge; 50 - comprehensive detection and controller; 51 - PID regulator; 52 - voltage comparator; 53 - peak detector; 54 - ultra-dynamic strain gauge. DETAILED DESCRIPTION

[0035] The technical scheme adopted by the present application is as follows:

[0036] An instrumented tensile impact fatigue test system of full electric measurement and control comprises a pulse emission module, a sample loading module, an automatic control module and a data acquisition module;

[0037] The pulse emission module comprises a stress wave riveting gun module and a pulse emission control circuit; the stress wave riveting gun module comprises a buffer element 32, a primary coil 33, a secondary coil 34 and a stress wave modulator 35; the buffer element 32, the primary coil 33 and the secondary coil 34 are all identical hollow cylinders; the stress wave modulator 35 is a circular cone; the bottom surface radius of the stress wave modulator 35 is the same as the bottom surface radius of the secondary coil 34; the stress wave modulator 35 is provided with a through hole in the axial direction; the radius of the through hole is the same as the inner ring radius of the secondary coil 34; the primary coil 33, the secondary coil 34 and the stress wave modulator 35 are sequentially arranged based on one bottom surface of the buffer element 32; after the buffer element 32, the primary coil 33, the secondary coil 34 and the stress wave modulator 35 are combined, the buffer element 32, the primary coil 33, the secondary coil 34 and the stress wave modulator 35 are coaxial; the through hole is connected with the inner ring of the buffer element 32, the inner ring of the primary coil 33 and the inner ring of the secondary coil 34 to form a through hole;

[0038] The primary coil 33 is connected with the pulse emission control circuit;

[0039] The pulse emission control circuit comprises a transformer 26, a rectifier silicon stack 27, a charging voltage detector 28, a vacuum switch 29, a voltage-time switch 30 and a capacitor group 31; one end of the vacuum switch 29 is connected with the primary coil 33; the other end of the vacuum switch 29 is connected with the charging voltage detector 28; the other end of the charging voltage detector 28 is respectively connected with one end of the rectifier silicon stack 27 and one end of the capacitor group 31; the other end of the rectifier silicon stack 27 is connected with the transformer 26; the other end of the transformer 26 is connected with the voltage-time switch 30; the other end of the capacitor group 31 is respectively connected with the voltage-time switch 30 and the primary coil 33;

[0040] The sample loading module is a Hopkinson pressure bar; the sample loading module includes a tensile incident bar 48, a tensile transmission bar 42, a dumbbell-shaped sample 46, an energy absorption and limiting device 38, and a damping stopper 39; the tensile incident bar 48 is horizontally arranged in the through hole; the tensile incident bar 48 is provided with a flange 36 at the end face close to the top of the stress wave modulator 35; the damping stopper 39 is cylindrical; the damping stopper 39 is fixed on the experimental rack; the damping stopper 39 is provided with threads; the damping stopper 39 is provided with the energy absorption and limiting device 38; the energy absorption and limiting device 38 is fixedly connected with the damping stopper 39 through threads; after the energy absorption and limiting device 38 is arranged in the damping stopper 39, the damping stopper 39 is filled with an energy absorption material; the energy absorption material is rubber clay or lead; the energy absorption and limiting device 38 is coaxial;

[0041] The other end face of the tensile incident bar 48 is provided with an incident bar trapezoidal groove 47; the incident bar trapezoidal groove 47 is a quadrangular pyramid; the end face of the tensile incident bar 48 is the bottom surface with the smallest area of the incident bar trapezoidal groove 47; the bottom surface with the smallest area and one side of the incident bar trapezoidal groove 47 are open; the dumbbell-shaped sample 46 is arranged in the incident bar trapezoidal groove 47; one end of the dumbbell-shaped sample 46 is arranged in the incident bar trapezoidal groove 47; the other end of the dumbbell-shaped sample 46 is arranged in a transmission bar trapezoidal groove 45 of a tensile transmission bar 42; one end of the tensile transmission bar 42 is provided with the transmission bar trapezoidal groove 45; the other end of the tensile transmission bar 42 is fixedly connected with a metal screw rod; the metal screw rod is fixedly connected with a lead screw driver 41; the transmission bar trapezoidal groove 45 is a quadrangular pyramid; the end face of the tensile transmission bar 42 is the bottom surface with the smallest area of the transmission bar trapezoidal groove 45; the bottom surface with the smallest area and one side of the transmission bar trapezoidal groove 45 are open; after the two ends of the dumbbell-shaped sample 46 are respectively arranged in the transmission bar trapezoidal groove 45 and the incident bar trapezoidal groove 47, a sample gap is arranged between the bottom surface with the largest area of the transmission bar trapezoidal groove 45 and the end of the dumbbell-shaped sample 46, and a sample gap is arranged between the bottom surface with the largest area of the incident bar trapezoidal groove 47 and the end of the dumbbell-shaped sample 46, so as to allow the dumbbell-shaped sample 46 to have sufficient moving space when compressed and loaded, not to constitute a compression mode, and to prevent accidental secondary tensile loading.

[0042] The lead screw driver 41 includes a lead screw driving motor and an LVDT linear displacement differential transformer 40; the LVDT linear displacement differential transformer 40 is used for measuring the displacement of the lead screw; the LVDT linear displacement differential transformer 40 and the lead screw driver 41 are both fixed on the experimental rack;

[0043] After the LVDT linear displacement differential transformer 40, the screw driver 41 and the sample loading module are installed, the tensile transmission rod 42, the dumbbell-shaped sample 46, the tensile incident rod 48 and the energy absorption and stopper 38 are collinear; a gap is arranged between the flange 36 and the energy absorption and stopper 38; the length of the gap is Δ; a gap photoelectric detector 37 is arranged directly above the gap; the length Δ of the gap is calculated in advance according to the tensile shock waveform and is a known quantity;

[0044] A first strain gauge 43 is arranged on the tensile transmission rod 42; a second strain gauge 49 is arranged on the tensile incident rod 48;

[0045] The automatic control module comprises a comprehensive detection and controller 50 and a peak detector 53; the comprehensive detection and controller 50 is a computer; the comprehensive detection and controller 50 is connected with the screw driver 41, the voltage-time switch 30, the gap photoelectric detector 37, the charging voltage detector 28 and the vacuum switch 29 respectively; the peak detector 53 is connected with the LVDT linear displacement differential transformer 40; the automatic control module is used for controlling the experimental system, resetting the transmission rod and the sample after loading through the electrical signal control, and ensuring single loading of the sample;

[0046] The data acquisition module comprises an ultra-dynamic strain gauge 54, the peak detector 53, a voltage comparator 52 and a PID regulator 51; the first strain gauge 43 is connected with the ultra-dynamic strain gauge 54; the second strain gauge 49 is connected with the ultra-dynamic strain gauge 54; the ultra-dynamic strain gauge 54, the peak detector 53, the voltage comparator 52 and the PID regulator 51 are connected with the comprehensive detection and controller 50; the data acquisition module is used for collecting data for real-time collection of shock force waveform, amplitude, displacement value, impact frequency and data;

[0047] A rubber sleeve 44 is arranged on the tensile incident rod 48, which is used for preventing the sample from falling off;

[0048] The material of the buffer element 32 is a high polymer material and steel, and the high polymer material is coated in the interior of the steel;

[0049] The primary coil 33 and the secondary coil 34 are wire windings;

[0050] The material of the stress wave modulator 35 is steel;

[0051] The length of the energy absorption and stopper 38 is greater than the wavelength of the stress wave generated by the system;

[0052] The materials of the energy absorption and stopper 38, the tensile transmission rod 42 and the tensile incident rod 48 are titanium alloy or aluminum alloy.

[0053] The present application is based on the principle of traditional high strain rate direct tensile Hopkinson bar, the stress wave modulator 8 of the stress wave riveting gun module in the prior art 1 is changed into coaxial hollow mode, allowing the non-magnetic Hopkinson incident bar to penetrate through, realizing high-energy high impact force, having idealized half-sine impact force waveform, and being controllable by computer.

[0054] The primary coil 33, the secondary coil 34 and the solid cone of the stress wave modulator 35 in the stress wave riveting gun module are changed into coaxial circular holes with an inner diameter of 14.1 mm, a circular straight rod with a diameter of 14 mm and a length of 1400 mm is used as a tensile incident bar 48, one end of which is provided with a flange 36 with a thickness of 5 mm and an outer diameter of 24 mm, after the tensile incident bar 48 passes through the coaxial circular hole, the flange 36 is in contact with the conical head end of the “stress wave riveting device”. In order to avoid electromagnetic influence, the rod is made of non-magnetic material such as titanium alloy, so that the impact pulse generated by the “stress wave riveting device” directly acts on the flange 36 of the tensile incident bar 48, generating a tensile pulse in the tensile incident bar 48.

[0055] The dumbbell-shaped sample is connected with the tensile incident bar and the transmission bar with slots to bear tensile loading and not compression loading; an energy absorber and a position limiter is arranged at the end of the flange platform of the incident bar to limit the deformation of the incident bar, and the end of the loading bar with slots is connected with the hook-type tensile sample to realize single-pulse impact loading; an electric screw with displacement measurement LVDT is arranged at the end of the transmission bar to realize the resetting of the transmission bar after loading, and the displacement in the impact fatigue process can be controlled.

[0056] In order to realize single impact single loading and prevent accidental secondary tensile loading, the tensile sample is designed into a dumbbell-shaped sample 46, the two ends of which are similar to trapezoidal or wedge-shaped bodies without threads, the connection between the tensile incident bar 48 and the tensile transmission bar 42 and the sample is changed into a hooking form, the trapezoidal grooves 47 of the incident bar and the trapezoidal grooves 45 of the transmission bar are used to connect with the sample, and the hooking grooves of the bars are left with gaps to allow the dumbbell-shaped sample 46 to have enough space to move when compression loading, and not to constitute a compression mode. In order to prevent the sample from sliding out of the slot during the impact fatigue process, an elastic rubber sleeve 44 is arranged at the end of the trapezoidal slot as shown in Figure 5 .

[0057] A solid rod with a diameter of 14 mm and a length of about 400 mm is arranged outside the flange 36 of the tensile incident bar 48, which is made of the same material as the tensile incident bar 48, as an energy absorber and position limiter 38, which is connected with a damping stopper 39 by threads and locked by a self-locking pin, when the tensile loading pulse is reflected in the tensile incident bar 48 for the second time to form a tensile pulse, there is no gap Δ between the flange 36 and the energy absorber and position limiter 38, so when the secondary tensile pulse enters the energy absorber and position limiter 38, the tensile incident bar 48 has no secondary tensile loading pulse.

[0058] A screw rod driver 41 is arranged at the end of the tensile transmission rod 42, and an LVDT linear displacement differential transformer 40 is arranged for measuring the displacement of the screw rod. The screw rod driver 41 allows the screw rod to freely extend and move towards the sample. Under the control of the electric control, the tensile transmission rod 42 is driven to move in the opposite direction of the sample, so that the sample is tightly combined with the tensile incident rod 48 and the tensile transmission rod 42, and bears the tensile impact load.

[0059] In order to realize single loading, the stress wave riveting gun module generates a tensile pulse at the tensile incident rod 48. The rod and the sample have a tendency to move to the right end. When the tensile pulse is reflected at the free end to form a compression pulse, it is transmitted to the flange 36 and reflected again to form a tensile pulse. The original reserved gap Δ disappears, and the stress wave pulse of the tensile incident rod 48 moving to the right is transmitted to the energy absorber and the stopper 38 through the flange 36, that is, the tensile incident rod 48 has no secondary tensile loading pulse.

[0060] The one-time impact load is transmitted to the tensile transmission rod 42 which is designed to be relatively short. The stress wave is transmitted back and forth in the rod, so that the rod moves towards the sample, causing the sample to be hooked out of contact with the rod, and also not to bear the secondary tensile load.

[0061] After the stress wave is transmitted back and forth in the two rods, the screw rod driver 41 is driven by the electric drive command to drive the tensile transmission rod 42, the dumbbell-shaped sample 46 and the tensile incident rod 48 to tightly contact, so as to meet the next impact load, and continue to repeat this process, that is, the impact fatigue loading cycle.

[0062] The strain signals of the transmission rod and the incident rod are collected, and the strain signals are amplified by a dynamic strain meter. At the same time, the signals pass through a peak detector and a voltage comparator. During the impact fatigue loading cycle, due to the decrease of the damage stiffness of the sample, the tensile force acting on the sample changes. At this time, the comparator outputs a signal to the comprehensive detection and controller, and the closed-loop adjustment of the capacitance charging voltage of the stress wave enhancement cone head is realized, so as to adjust the loading load, and realize the closed-loop control of the stable maintenance of the impact force amplitude.

[0063] The measured signals of the first strain gauge 43 and the second strain gauge 49 are introduced into the super dynamic strain meter 54, the peak detector 53 and the voltage comparator 52 respectively and compared with the predetermined values. If the amplitude of the impact force signal of the tensile incident rod 48 or the tensile transmission rod 42 decreases, the adjusting voltage is given through the voltage comparator 52 and the PID regulator 51. At this time, the output instruction signal of the comprehensive detection and control device 50 adjusts the voltage-time switch 30 of the "stress wave riveting device". The increased voltage signal is high, the time relay switch is closed for a long time, the required voltage of the capacitor bank 31 can be higher, and the vacuum switch 29 is controlled to be turned on. The closed-loop corrected impact loading pulse amplitude is generated in the tensile transmission rod 42. During the experiment, the gap Δ between the flange 36 and the energy absorption and limiting device 38 is detected by the gap photoelectric detector 37. If the gap changes, the comprehensive detection and control device 50 gives an indication and a warning.

[0064] The impact displacement is kept: in the impact fatigue process, in order to monitor the displacement change of the sample, or to carry out the impact fatigue test of the tensile displacement, the lead screw drag 41 has the LVDT linear displacement differential transformer 40 outputting the displacement signal. The signal is sent into the comparator and compared with the predetermined displacement value after being converted from alternating current to direct current and peak detection. If the amplitude changes during loading, the comparator outputs the increase or decrease difference value to the PID regulator 51 and then to the comprehensive detection and control device 50. The control device outputs the control of the voltage-time switch 30 of the "stress wave riveting device" to control the charging time, so that the capacitor bank 31 is charged to the required voltage, and the closed-loop displacement control is achieved.

[0065] The impact force, impact waveform and impact number are displayed and indicated: the strain gauge detection signals of the tensile transmission rod 42 and the tensile incident rod 48 are introduced into the comprehensive detection and control device 50. The comprehensive detection and control device 50 has the waveform display, peak value and impact number counting and display functions. At the same time, the impact number can be preset. The experiment is stopped when the predetermined number is reached.

[0066] The application is further described below in combination with the drawings and examples.

[0067] Reference Figure 4 ,

[0068] 1) The stress wave riveting gun module is used as the source of the high strain rate impact tensile pulse. The buffer element 32, the primary coil 33, the secondary coil 34 and the stress wave modulator 35 are integrally made into the gun head with a coaxial through hole of 14.1 mm in the center axis. The outer diameter of the tapered head end of the stress wave modulator 35 is 24 mm. The stress wave riveting gun module can generate a peak force of 10 kN and a stress wave pulse width of not more than 200 μs.

[0069] 2) The standard bar loading method of the traditional direct tension Hopkinson bar is used as reference and modified. A titanium alloy tensile incident bar 48 with a diameter of 14 mm and a length of 1400 mm is made. One end of the bar is made into a flange 36 with a thickness of 5 mm and an outer diameter of 24 mm. The other end is made into a notch with a trapezoidal shape and a slot width of 8 mm and a slot depth of 10 mm, which can hook the tensile sample. The tensile transmission bar 42 has a diameter of 14 mm and a length of 1000 mm. The bar end is slotted and the same as the tensile incident bar 48. The other end has a M5 threaded hole with a depth of 15 mm. A titanium alloy energy absorption and stopper 38 with a diameter of 14 mm and a length of 600 mm is made. The other end has a M14 threaded hole. The titanium alloy material of these bars is non-magnetic. In addition, the sample for high strain rate impact tensile fatigue needs to be made into a dumbbell-shaped sample 46. The center of the sample is a straight section with a diameter of 5 mm or a plate with a width of 5 mm. The two ends are made into a trapezoidal shape and are connected by hooking the trapezoidal grooves of the tensile incident bar 48 and the tensile transmission bar 42. A rubber sleeve 44 is fitted on the hooking groove to prevent the sample from sliding out of the groove when being stretched.

[0070] 3) The stress wave riveting gun module, the tensile incident bar 48, the dumbbell-shaped sample 46, the tensile transmission bar 42 and the energy absorption and stopper 38 are installed on the same axis on the horizontal heavy support with a width of 200 mm and a length of 3500 mm according to the layout Figure 4 . The flange 36 of the tensile incident bar 48 is in close contact with the tapered head end of the stress wave modulator 35, and there is a △ gap between the flange 36 and the energy absorption and stopper 38. This gap can be calculated in advance according to the required tensile impact waveform and is a known quantity. The M14 threaded end of the energy absorption and stopper 38 is threadedly locked with a damping stopper 39. The threads cannot be loosened during the impact test, and the damping stopper 39 is fixedly connected with the overall frame. The other end of the tensile transmission bar 42 is connected with a screw rod actuator 41 through a M5 metal screw rod. The actuator is equipped with a lead screw driving motor and a LVDT linear displacement differential transformer 40 for measuring the displacement of the lead screw.

[0071] 4) No. 2 strain gauges 49 and no. 1 strain gauges 43 are attached to the outer surfaces of the tensile incident bar 48 and the tensile transmission bar 42 at half the length, respectively. 5AA high-precision strain gauges are used, and two are attached symmetrically on the outer surface of the bar with epoxy glue. These strain gauges are connected in full-bridge mode and then connected to an ultra-dynamic strain meter 54, a peak detector 53, a voltage comparator 52, a PID regulator 51 and a comprehensive detection and controller 50. The output of the LVDT linear displacement differential transformer 40 is also introduced into the peak detector 43, the voltage comparator 52, the PID regulator 51 and the comprehensive detection and controller 50. The voltage of the voltage comparator 52, the charging voltage and the counter, the force and displacement waveform are all displayed on the computer display screen of the comprehensive detection and controller 50.

[0072] 5) In the stress wave riveting gun module charging circuit part, install voltage-time switch 30, the voltage size of this switch controls the on circuit, that is, different voltages correspond to different on times, and also install charging voltage detector 28.

[0073] Tensile impact fatigue test steps:

[0074] First step: see Figure 4 , dumbbell-shaped sample 46 is loaded into the clamping groove of tensile incident rod 48 and tensile transmission rod 42, and is closed by rubber sleeve 44 which prevents the sample from sliding out of the slotted groove. The rubber sleeve is non-metallic and elastic, and does not affect the transmission of stress wave signals during impact.

[0075] Second step: operate computer mode comprehensive detection and controller 50 to make lead screw drag 41 tension tensile transmission rod 42, dumbbell-shaped sample 46 and tensile incident rod 48, that is, set a very small tensioning force F in advance in comprehensive detection and controller 50 as the criterion for tensioning, while LVDT linear displacement differential transformer 40 attached to lead screw drag 41 records the displacement value of tensioning, and this value is zeroed as the displacement zero point. The displacement value can be displayed in real time in comprehensive detection and controller 50.

[0076] Third step: according to the impact force signal required by the dynamic impact of the sample, the size of gap Δ can be calculated. Based on the reference of flange 36 of tensile incident rod 48, adjust energy absorption and stopper 38 and damping stopper 39, lock the stop and leave gap Δ.

[0077] Fourth step: through the impact force signal input by comprehensive detection and controller 50 in the previous step, calculate the voltage value of capacitor bank 31, and input the impact frequency in comprehensive detection and controller 50. The wave form real-time display mode can display the wave form of No. 1 strain gauge 43 and No. 2 strain gauge 49 and detection in real time.

[0078] Fifth step: start the test. After the first impact, voltage comparator 32 and comprehensive detection and controller 50 compare the signal amplitude of No. 1 strain gauge 43 and No. 2 strain gauge 49 with the predetermined value. If the condition is met, the second impact test will be automatically continued according to the input impact frequency requirement. If the condition is not met, comprehensive detection and controller 50 will output command signal to voltage-time switch 30 at this time. Voltage is converted into corresponding charging time to control the change of charging time of capacitor bank 31, and then the adjusted voltage is obtained to give command to comprehensive detection and controller 50 to continue the test.

[0079] Sixth step: If the sample is broken, the impact displacement and impact force value given by the comprehensive detection and controller 50 protection, for example, can be set to exceed 50% of the predetermined value, the comprehensive detection and controller 50 gives the stop command. In addition, when the experiment wants to stop, press the stop button of the comprehensive detection and controller 50, the experiment can be stopped.

[0080] During the experiment, the impact force waveform, amplitude, displacement value, impact frequency and frequency are displayed in real time by the comprehensive detection and controller 50.

[0081] The above is the impact force closed-loop control fatigue test, and the impact displacement closed-loop control experiment process is the same, except that the force amplitude setting is changed to displacement control mode.

Claims

1. A fully electrically controlled instrumented tensile impact fatigue test system, characterized in that: The application relates to a stress wave riveting gun module, a sample loading module, a screw rod dragger (41) and a metal screw rod; the stress wave riveting gun module comprises a stress wave riveting gun module and a pulse emission control circuit; the sample loading module is a Hopkinson pressure bar; the sample loading module comprises a tensile incident rod (48), a tensile transmission rod (42), a dumbbell-shaped sample (46) and a damping module; the damping module comprises an energy absorption and limiting device (38) and a damping stopper (39); the screw rod dragger (41) comprises a screw rod driving motor and an LVDT linear displacement differential transformer (40); the stress wave riveting gun module comprises a buffer element (32), a primary coil (33), a secondary coil (34) and a stress wave modulator (35); the buffer element (32), the primary coil (33) and the secondary coil (34) are all hollow cylinders; the stress wave modulator (35) is a conical body; the bottom surface radius of the stress wave modulator (35) is the same as that of the secondary coil (34); the stress wave modulator (35) is provided with a through hole in the axial direction; the radius of the through hole is the same as that of the inner ring of the secondary coil (34); the primary coil (33), the secondary coil (34) and the stress wave modulator (35) are sequentially arranged on the basis of one bottom surface of the buffer element (32); after the buffer element (32), the primary coil (33), the secondary coil (34) and the stress wave modulator (35) are combined, the buffer element (32), the primary coil (33), the secondary coil (34) and the stress wave modulator (35) are coaxial; the through hole, the inner ring of the buffer element (32), the inner ring of the primary coil (33) and the inner ring of the secondary coil (34) are connected to form a through hole; the primary coil (33) is connected with the pulse emission control circuit; the tensile incident rod (48) is horizontally arranged in the through hole; a flange (36) is arranged on the end surface of the tensile incident rod (48) close to the vertex of the stress wave modulator (35); the damping stopper (39) is a cylindrical body; the damping stopper (39) is fixed on an experimental rack; the energy absorption and limiting device (38) is arranged in the damping stopper (39); the energy absorption and limiting device (38) is a metal rod; a gap is arranged between the flange (36) and the energy absorption and limiting device (38); the length of the gap is delta; one end of the tensile transmission rod (42) is connected with the dumbbell-shaped sample (46); the other end of the tensile transmission rod (42) is fixedly connected with one end of the metal screw rod; the other end of the metal screw rod is fixedly connected with the screw rod dragger (41); the LVDT linear displacement differential transformer (40) and the screw rod dragger (41) are both fixed on the experimental rack; after the LVDT linear displacement differential transformer (40), the screw rod dragger (41) and the sample loading module are installed, the tensile transmission rod (42), the dumbbell-shaped sample (46), the tensile incident rod (48), the metal screw rod and the energy absorption and limiting device (38) are collinear.

2. The fully electrically controlled instrumented tensile impact fatigue test system according to claim 1, characterized in that: The damping stopper (39) is provided with threads; the energy absorption and limiting device (38) is fixedly connected with the damping stopper (39) through threads; after the energy absorption and limiting device (38) is arranged in the damping stopper (39), the damping stopper (39) is filled with energy absorption materials; the energy absorption and limiting device (38) is coaxial.

3. The fully electrically controlled instrumented tensile impact fatigue test system according to claim 1, characterized in that: The end face of the tensile incident rod (48) connected with the dumbbell-shaped sample (46) is provided with an incident rod trapezoidal groove (47); the incident rod trapezoidal groove (47) is a quadrangular pyramid; the bottom surface with the smallest area of the incident rod trapezoidal groove (47) is the end face of the tensile incident rod (48); the bottom surface with the smallest area and one side of the incident rod trapezoidal groove (47) are open; the dumbbell-shaped sample (46) is arranged in the incident rod trapezoidal groove (47); one end of the dumbbell-shaped sample (46) is arranged in the incident rod trapezoidal groove (47); the other end of the dumbbell-shaped sample (46) is arranged in the transmission rod trapezoidal groove (45) of the tensile transmission rod (42); the transmission rod trapezoidal groove (45) is a quadrangular pyramid; the bottom surface with the smallest area of the transmission rod trapezoidal groove (45) is the end face of the tensile transmission rod (42); the bottom surface with the smallest area and one side of the transmission rod trapezoidal groove (45) are open; after the two ends of the dumbbell-shaped sample (46) are respectively arranged in the transmission rod trapezoidal groove (45) and the incident rod trapezoidal groove (47), a sample gap is arranged between the bottom surface with the largest area of the transmission rod trapezoidal groove (45) and the end of the dumbbell-shaped sample (46), and a sample gap is arranged between the bottom surface with the largest area of the incident rod trapezoidal groove (47) and the end of the dumbbell-shaped sample (46).

4. The fully electrically controlled instrumented tensile impact fatigue test system according to claim 1, characterized in that: The length of the energy absorption and limiting device (38) is greater than the wavelength of the stress wave generated by the system; the length Δ of the gap is obtained in advance according to the tensile shock wave form.

5. The fully electrically controlled instrumented tensile impact fatigue test system according to claim 4, characterized in that: The pulse emission control circuit comprises a transformer (26), a rectifier silicon stack (27), a charging voltage detector (28), a vacuum switch (29), a voltage-time switch (30) and a capacitor group (31); one end of the vacuum switch (29) is connected with the primary coil (33); the other end of the vacuum switch (29) is connected with the charging voltage detector (28); the other end of the charging voltage detector (28) is respectively connected with one end of the rectifier silicon stack (27) and one end of the capacitor group (31); the other end of the rectifier silicon stack (27) is connected with the transformer (26); the other end of the transformer (26) is connected with the voltage-time switch (30); the other end of the capacitor group (31) is respectively connected with the voltage-time switch (30) and the primary coil (33).

6. The fully electrically controlled instrumented tensile impact fatigue test system according to claim 5, characterized in that: The gap photoelectric detector (37) is arranged directly above the gap.

7. The fully electrically controlled instrumented tensile impact fatigue test system according to claim 6, characterized in that: A first strain gauge (43) is arranged on the tensile transmission rod (42); a second strain gauge (49) is arranged on the tensile incident rod (48).

8. The fully electrically controlled instrumented tensile impact fatigue test system according to claim 7, characterized in that: The all-electric instrumented tensile impact fatigue test system comprises an automatic control module and a data acquisition module; the automatic control module comprises a comprehensive detection and controller (50) and a peak detector (53); the comprehensive detection and controller (50) is a computer; the comprehensive detection and controller (50) is connected with a screw drive (41), a voltage-time switch (30), a gap photoelectric detector (37), a charging voltage detector (28) and a vacuum switch (29) respectively; the peak detector (53) is connected with an LVDT linear displacement differential transformer (40); the data acquisition module comprises an ultra-dynamic strain gauge (54), a peak detector (53), a voltage comparator (52) and a PID regulator (51); the first strain gauge (43) is connected with the ultra-dynamic strain gauge (54); the second strain gauge (49) is connected with the ultra-dynamic strain gauge (54); the ultra-dynamic strain gauge (54), the peak detector (53), the voltage comparator (52) and the PID regulator (51) are all connected with the comprehensive detection and controller (50).

9. The fully electrically controlled instrumented tensile impact fatigue test system according to claim 8, characterized in that: A rubber sleeve (44) is arranged on the tensile incident rod (48) to prevent the sample from falling off.

10. The fully electrically controlled instrumented tensile impact fatigue test system according to claim 1, characterized in that: The primary coil (33) and the secondary coil (34) are both wire windings; the stress wave modulator (35) is made of steel; the buffer element (32) is made of a high polymer material and steel, and the high polymer material is coated in the inside of the steel; the energy-absorbing material is plasticine or lead.

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