A device for underwater low velocity drop hammer impact test

Abstract

The application discloses a device for underwater low-speed drop hammer impact test, which comprises a drop hammer loading control subsystem for providing controllable energy repeated low-speed impact load; an underwater environment simulation subsystem comprising a sealed container and a water injection device for completely immersing a test sample in water and maintaining a saturated water pressure state; a multi-source signal synchronous acquisition subsystem for acquiring test sample surface morphology change data and test sample boundary displacement response data in real time during the impact process; an intelligent control subsystem connected with the multi-source signal synchronous acquisition subsystem; wherein the drop hammer loading subsystem, the underwater environment simulation subsystem, the multi-source signal synchronous acquisition subsystem and the intelligent control subsystem are integrated in the same physical platform. The novel drop hammer impact test device of the application is particularly suitable for the scene of high-performance fiber composite material repeated impact test of tens of thousands of times, and can significantly improve the test efficiency and reduce the artificial workload.

Description

Technical Field

[0001] This invention belongs to the field of marine engineering research technology, and in particular relates to a device for underwater low-speed drop hammer impact testing. Background Technology

[0002] Impact loads are one of the most significant dynamic loads faced by engineering structures, commonly occurring in complex conditions such as earthquakes, vehicle collisions, freeze-thaw cycles, and marine environments. To assess the safety and durability of materials under dynamic loads, impact testing has become a crucial method for studying their impact resistance, energy absorption capacity, and fracture behavior. Especially in fields such as hydraulic engineering, bridge structures, and marine infrastructure, materials are often exposed to prolonged water saturation or humid environments, which can lead to significant degradation of their mechanical properties. Therefore, conducting dynamic mechanical property tests under water saturation conditions is of great importance for accurately reflecting the service performance of materials.

[0003] Currently, commonly used impact testing methods mainly include pendulum impact, falling hammer impact, and split Hopkinson bar (SHPB). Among them, the Charpy pendulum impact test is widely used due to its simplicity and low cost, but its test results are greatly affected by human operation factors, and it is difficult to achieve continuous data acquisition during the impact process, which limits the in-depth analysis of the dynamic response mechanism of materials. Although the split Hopkinson bar (SHPB) technology can achieve dynamic loading at high strain rates and accurately capture stress wave signals through strain gauges, it is usually suitable for small-sized specimens, and the loading pulse duration is short. It is mainly used to study high-speed impact behavior and is difficult to simulate the low-speed, long-term impact processes commonly seen in engineering.

[0004] Drop hammer impact testing, a classic low-velocity impact testing method, adjusts impact energy by controlling the mass and drop height of the hammer. It offers advantages such as intuitive loading methods, a wide range of sample sizes, and the ability to simulate real-world engineering impact scenarios, making it widely used for evaluating the impact resistance of brittle or quasi-brittle materials like concrete and fiber-reinforced composites. Existing research has used the drop hammer method to test the impact resistance of ultra-high toughness cement-based composites, analyzing damage evolution and energy absorption mechanisms under impact loads by recording indicators such as the number of initial cracks, the number of failures, and impact energy dissipation. However, existing drop hammer devices generally have the following limitations: First, most devices lack effective environmental simulation systems, making in-situ impact testing of samples under saturated water pressure impossible, resulting in a disconnect between test conditions and actual service environments; second, they lack real-time monitoring capabilities for key dynamic parameters such as impact force and stress wave propagation during the impact process, making it difficult to reveal the stress transmission and crack propagation mechanisms within the material; and third, some devices lack reliable anti-secondary impact mechanisms, affecting the accuracy and repeatability of test data.

[0005] Existing drop hammer impact testing devices have shortcomings in underwater environment simulation capabilities, dynamic data acquisition accuracy, and test condition realism, especially lacking a dedicated testing system for the low-velocity impact behavior of materials in underwater environments. This invention aims to address these issues by developing a novel drop hammer impact testing device that integrates environmental simulation, precise loading, and simultaneous multi-parameter acquisition. This device will not only improve the scientific rigor and reliability of dynamic performance testing of materials but also provide strong support for the research and engineering application of high-performance building materials. Summary of the Invention

[0006] The main objective of this invention is to provide a test device for underwater low-speed drop hammer impact, which is suitable for studying the dynamic impact loading of brittle and semi-brittle material samples such as concrete and fiber-reinforced composite materials.

[0007] This invention is achieved through the following technical solution: An apparatus for underwater low-velocity drop hammer impact testing, comprising: The drop hammer loading control subsystem includes a support frame and two liftable sliding rails; used to provide repetitive low-speed impact loads with controllable energy; The underwater environment simulation subsystem includes a sealed container and a boundary response contact module. The sealed container consists of a base and an open top plate, used to completely immerse the sample in water and maintain a saturated water pressure. The boundary response contact module includes a constraint plate and an electromagnetic induction unit. Each electromagnetic induction unit contains a energized coil and is connected to an iron constraint plate. When the sample contacts any side of the constraint plate, a closed loop is formed, and the loop conduction triggers the generation of a current signal. The multi-source signal synchronous acquisition subsystem includes an optical morphology measurement module and a boundary response contact module. The optical morphology measurement module is installed on the drop hammer loading control system, and the boundary response contact module is installed on the underwater environment simulation subsystem. During the impact process, the system acquires real-time data on the surface morphology changes of the sample and the boundary displacement response data of the sample. The intelligent control subsystem includes a computer and a data exchange, and is connected to the multi-source signal synchronous acquisition subsystem for signal transmission and data storage. The drop hammer loading subsystem, the underwater environment simulation subsystem, the multi-source signal synchronous acquisition subsystem, and the intelligent control subsystem are integrated on the same physical platform. The subsystem automatically collects the number of initial impacts, the number of destructive impacts, the energy consumption per unit mass of impact, and the ductility coefficient of the sample, and generates a test report.

[0008] Furthermore, in the drop hammer loading control subsystem, the support frame is composed of a sliding rail, a metal base plate, and a metal top plate. The two liftable vertical sliding rails are fixedly mounted on the metal base plate. The two liftable vertical sliding rails are rigidly connected to the metal top plate. The first liftable vertical sliding rail is equipped with an industrial camera as an optical topography measurement module. The second liftable vertical sliding rail is equipped with an electromagnet as a drop hammer adsorption and release mechanism.

[0009] Specifically, the sliding track surface is marked with graduations for height position calibration, and the height position of the track is digitally controlled by the winch operated by the intelligent control subsystem.

[0010] Specifically, the drop hammer adsorption and release mechanism is any one of an electromagnetic adsorption mechanism, a vacuum adsorption mechanism, or a mechanical clamping mechanism; Specifically, the electromagnet on the second liftable vertical sliding track is used to attract and release the metal hammer; after the magnetic force is eliminated by power-off, the hammer falls freely; subsequently, the second liftable vertical sliding track moves downward along a vertical path to retrieve the hammer, and then returns upward to a preset height to realize a continuous impact test cycle; the weight of the hammer can be changed according to the test requirements, and its cross-sectional size is adapted to the test sample and is less than or equal to the diameter of the cross-section of the test sample to ensure uniform transmission of impact load.

[0011] Furthermore, in the underwater environment simulation subsystem, the base is made of welded metal, and the base is bolted to the open top plate; The opening top plate is designed to be detachable for placing samples and injecting water; The center of the open top plate is also provided with a mounting hole that is adapted to the shape of the force dispersion structure; the force dispersion structure, which is placed directly above the sample, has a continuous curved surface on its lower surface, which is used to evenly distribute the impact load of the drop hammer to the top surface of the sample. The force-dispersing structure is any one of a spherical, ellipsoidal, frustum conical, or ring-shaped rigid body.

[0012] Furthermore, in the multi-source signal synchronous acquisition subsystem, the optical morphology measurement module is an industrial camera, mounted on the camera bracket of the first liftable vertical sliding track of the drop hammer loading control subsystem, used to acquire the full-field surface displacement field and strain field of the sample during the impact process; it includes at least one boundary contact response module, used to monitor the change in contact state between the sample and its surrounding constraint structure under impact; the specimen morphology measurement module is any one of a digital image correlation (DIC) system, a laser scanning vibrometer, or a structured light 3D reconstruction system; the boundary contact response module is a contact sensing unit based on the principles of electromagnetic induction, capacitance change, resistance switching, or optical blocking.

[0013] Furthermore, the intelligent control subsystem is electrically connected to the multi-source signal synchronous acquisition subsystem to acquire, store, and analyze image data of the sample after it has been subjected to a drop hammer impact; it can identify the moment when the sample first shows macroscopic damage based on the sample surface morphology change data and record the corresponding number of impacts; based on the sample boundary displacement response data, it can identify the moment when the sample undergoes critical plastic deformation and record the corresponding number of impacts; when the moment of plastic deformation is identified, the impact test process is automatically terminated, and a test report containing the number of impacts is output; the test report includes the number of initial crack impacts and the number of destructive impacts, or the energy consumption per unit mass of impact and the plastic deformation ductility coefficient.

[0014] Specifically, the shape of the sample is any one of cylinder, prism or frustum, and its dimensions satisfy: diameter or side length not less than 50 mm and not more than 200 mm, and height-to-diameter ratio between 1.5:1 and 3:1.

[0015] Specifically, during underwater low-speed drop hammer impact, the low-speed impact is defined as follows: the final velocity of the drop hammer does not exceed 5 m / s, the impact energy is adjustable within the range of 10 J–500 J, and the duration of a single impact is greater than 10 ms. The beneficial effects of this invention are as follows: This invention innovatively integrates four functional modules—saturated water pressure environment simulation, controllable low-speed repetitive impact loading, synchronous sensing of multi-source heterogeneous signals, and intelligent criterion-driven decision-making—into a single physical platform. This fundamentally solves the four major bottlenecks in existing underwater material dynamic performance testing technologies: environmental distortion, process black box, subjective criteria, and low efficiency. It achieves a synergistic leap in experimental scientific rigor, data completeness, and engineering practicality. Specifically, this is manifested in the following five substantial technological advancements: 1) For the first time, in-situ mapping of "real service environment - dynamic mechanical response" was achieved, overcoming the problem of environmental simulation distortion; 2) Unlike traditional crude tests that only record the number of impacts or macroscopic damage, this invention achieves quantitative evaluation through spatiotemporal synchronous acquisition of an optical morphology measurement module (industrial camera + DIC algorithm) and a boundary response contact module (four sets of electromagnetic induction units); 3) To address the problem of load distortion caused by splashing, rebounding, and eccentricity in underwater drop hammers, this invention proposes a closed-loop control system of electromagnetic adsorption-power-off release-track recovery. By releasing the drop hammer instantaneously upon power failure, it achieves free fall with zero initial velocity, avoiding inertial interference from mechanical release mechanisms. After the drop hammer impacts the ground, the track automatically moves down to pick up and reset the hammer, completely eliminating the risk of secondary impact. 4) Achieve intelligent decision-making throughout the entire process of "image recognition - signal judgment - automatic termination - report generation", eliminating reliance on manual intervention; 5) Establish a standardized evaluation paradigm for engineering life prediction to support material research and development and standard upgrades. The indicators output by this invention constitute a quantifiable underwater impact resistance durability evaluation matrix. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the intelligent control subsystem and the drop hammer loading control subsystem of the present invention; Figure 2 This is a schematic diagram of the underwater environment simulation subsystem of the present invention; Figure 3 This is a cross-sectional structural diagram of the underwater environment simulation subsystem of the present invention; Reference numerals: 1-Metal top plate; 2-First liftable vertical sliding track; 3-Second liftable vertical sliding track; 4-Camera bracket; 5-Electromagnet; 6-Metal base plate; 7-Intelligent control subsystem; 8-Falling hammer; 9-Spherical dispersion; 10-Open top plate; 11-Electromagnetic induction unit; 12-Lid; 13-Base; 14-Sample; 15-Constraint plate. Detailed Implementation

[0017] The invention will be further described with reference to the accompanying drawings.

[0018] like Figure 1 , Figure 2 and Figure 3 As shown, a test device for underwater low-speed drop hammer impact includes a drop hammer loading control subsystem, a multi-source signal synchronous acquisition subsystem, an underwater environment simulation subsystem, and an intelligent control subsystem 7. An industrial camera, as an optical topography measurement module, is mounted on a camera bracket 4 on the first liftable vertical sliding rail 2 of the drop hammer loading control subsystem.

[0019] The drop hammer loading control subsystem includes a support frame consisting of sliding rails, a metal base plate 6, and a metal top plate 1, and two liftable sliding rails bolted to the metal base plate 6. The two liftable sliding rails include a first liftable vertical sliding rail 2 and a second liftable vertical sliding rail 3. Both sliding rails are bolted to the metal base plate 6 and the metal top plate 1. A camera bracket 4 is mounted on the first liftable vertical sliding rail 2 for mounting an industrial camera as an optical topography measurement module. An electromagnet 5 is mounted on the second liftable vertical sliding rail 3 as a drop hammer adsorption and release mechanism for adsorbing and releasing the drop hammer 8. After the magnetic force is eliminated by power-off, the drop hammer 8 falls freely. The drop hammer 8 is cylindrical, and its cross-sectional dimensions are adapted to the geometry of the sample 14 to ensure uniform distribution of impact stress. Its weight can be changed according to testing requirements, and its cross-sectional dimensions are adapted to the test sample 14 to ensure uniform transmission of impact load. Both of the liftable sliding rails have graduations on their surfaces for height calibration. The second liftable vertical sliding rail 3 then moves downwards along a vertical path to retrieve the drop hammer 8, before returning upwards to the preset height, thus completing a continuous impact test cycle. The height of the rails is digitally controlled by the winch operated by the intelligent control subsystem 7. Both sliding rails are rigidly connected to the metal base plate 6, ensuring the verticality of the impact path of the drop hammer 8 and the stability of the system.

[0020] The intelligent control subsystem 7 includes a computer and a data exchange, and is connected to the optical topography measurement module and boundary response contact module of the multi-source signal synchronous acquisition subsystem via a data cable. The intelligent control subsystem 7 stores and analyzes image data acquired by an industrial camera; after the sample is impacted by a drop hammer 8, based on the image data, the intelligent control system determines the moment when the first crack appears and records the number of drop hammer impacts. After receiving the electrical signal from the boundary response contact module, the intelligent control subsystem 7 determines that this is the moment when sample 14 fails and records the current number of hammer impacts. And stop the test. The specific implementation process is as follows: The computer-controlled winch adjusts the height of the two sliding tracks; it collects and stores DIC image data acquired by the industrial camera; based on the image data, it records the number of hammer impacts when the first crack appears on sample 14 after impact. The signal output from the boundary response contact module of specimen 14 is collected to determine the moment when specimen 14 undergoes critical plastic deformation. The number of drop hammer impacts is recorded when specimen 14 contacts any three of the four faces of the constraint plate 15 after deformation. The test was then terminated. Based on the collected impact number data, the performance indicators of the specimen 14 against low-velocity impacts were calculated, including but not limited to the number of initial crack impacts, the number of destructive impacts, the energy consumption per unit mass of impact, and the ductility coefficient.

[0021] ; ; ; in The number of times the sample withstood drop hammer impacts during the plastic stage. As an indicator of the energy dissipation of the sample, This is an indicator of the sample's ductility; The weight of the cylindrical metal drop hammer 8. It is the acceleration due to gravity. The release height of the drop hammer 8. The specimen 14 is a cylindrical geometric body adapted to the inner dimensions of the constraint plate 15 in the underwater environment simulation subsystem, and its cross-sectional projected area is smaller than the area enclosed by the inner boundary of the limiting groove. The specimen 14 is placed centrally inside the constraint plate 15, and its side surface maintains a uniform gap with the circumferential constraint plate 15. The size of this gap is dynamically set according to the expected deformation of the specimen 14 to ensure that the specimen 14 does not contact the constraint surface in the undeformed state.

[0022] The underwater environment simulation subsystem is used to construct an impact test scenario for sample 14 under saturated water pressure. It includes a sealed container and a boundary response contact module. The sealed container consists of a base 13 and an open top plate 10. The base 13 and the cover 12 are bolted together, and the open top plate 10 is a detachable structure (including but not limited to snap-on disassembly and ring clamp fixation) to accommodate sample 14 and water injection. The base 13, cover 12, and open top plate 10 together form a closed container. The base 13 is welded from metal, seamless, and watertight. Water is injected into the closed container to simulate an underwater environment.

[0023] The center of the opening top plate 10 is also provided with a mounting hole adapted to the shape of the force dispersion structure; the force dispersion structure, placed directly above the sample 14, has a continuous curved surface on its lower surface to evenly distribute the impact load of the falling hammer to the top surface of the sample 14; the force dispersion structure can be any one of a sphere, ellipsoid, frustum conical, or annular rigid body; the opening top plate 10 has a slot at its center and a steel plate is welded around the opening. A force dispersion structure (in this embodiment, a spherical dispersion body 9) is placed in the slot to evenly transmit the impact force of the falling hammer 8 to the top of the sample 14; In the impact test scenario under saturated water pressure, the sample 14 is placed on the pressure vessel base 13, and water is injected into the vessel until the sample 14 is completely submerged, forming a steady-state saturated water pressure environment. A curved contact force dispersion structure is set directly above the sample 14 to evenly distribute the impact load of the drop hammer to the top surface of the sample 14. A circumferential constraint plate 15 structure is configured to surround the sample 14. When the sample 14 undergoes plastic deformation under impact, the boundary response contact module is triggered. This module transmits the contact response signal to the intelligent control subsystem 7. The subsystem sends a termination command based on the contact response signal, records the current number of impacts, and ends the test process.

[0024] The boundary response contact module is mounted on the top plate 10 of the opening and consists of four sets of electromagnetic induction units 11 and a constraint plate 15. Only one set of electromagnetic induction units 11 is shown in the figure. Each electromagnetic induction unit 11 contains a energized coil and is connected to an iron constraint plate 15. When the sample 14 contacts any side of the constraint plate 15, a closed loop is formed, and the loop conduction triggers the generation of a current signal. Therefore, when the sample 14 contacts any three sides of the constraint plate 15, the current signal is transmitted to the intelligent control subsystem 7, which records the number of times the current hammer impact is triggered. And issue an instruction to terminate the test.

[0025] The specific implementation steps of the embodiments of the present invention are as follows: The high-performance fiber composite material sample 14 was subjected to drop hammer impact loading using the invented drop hammer impact testing device. After adjusting the specified heights of the first liftable vertical sliding rail 2 and the second liftable vertical sliding rail 3 through the intelligent control subsystem 7, an industrial camera was installed on the sliding rail 2. The electromagnet 5 was energized through the intelligent control subsystem 7 to obtain magnetic force, which attracted the metal drop hammer 8 to the electromagnet 5 on the second liftable vertical sliding rail 3. The sample 14 was placed at the center of the base 13 of the underwater environment simulation subsystem, and water was poured into the sealed container of the underwater environment simulation subsystem to immerse the sample 14 until it reached a saturated state.

[0026] The test begins on the intelligent control subsystem 7. Electromagnet 5 is de-energized, and the metal drop hammer 8 falls freely, impacting the spherical disperser 9. The impact force is dispersed onto the surface of the sample 14. Electromagnet 5 on the second liftable vertical sliding track 3 moves downwards to pick up the metal drop hammer 8. After rising to a preset height, the metal drop hammer 8 is released repeatedly. When the first crack appears on the sample 14 after being impacted by the drop hammer, the intelligent control subsystem 7 records the number of impacts. When the specimen 14 deforms and contacts three of the four sides of the constraint plate 15, the intelligent control subsystem 7 records the number of impacts from the falling hammer. The intelligent control subsystem 7 calculates the performance indicators of sample 14 against low-velocity impacts, and then terminates the test. , , The specific test data is shown in Table 1: Table 1 As can be seen from the test data in Table 1 above, the device of the present invention can stably and repeatedly output a very large range. The values ​​(from 145 to 10365) demonstrate that its "electromagnetic adsorption-power failure release-track recovery closed-loop control" maintains high reliability even after long-term underwater operation, and the intelligent control subsystem 7 can accurately record up to tens of thousands of impacts without omissions or misjudgments; furthermore, using "three out of four sides of the contact constraint plate after deformation" as the failure criterion, the device can accurately sense and record deformation. Furthermore, it is applicable to both materials, proving that its underwater environment simulation subsystem has good sealing performance and sensitivity underwater; and after completing tens of thousands of cycles, there is still no delay or failure, indicating that the underwater durability, corrosion resistance and fatigue life of the moving mechanism of the device meet the requirements of long-cycle testing, which can significantly improve testing efficiency and reduce manual workload.

[0027] In summary, based on the typical test results shown in Table 1, this device can quickly distinguish between brittle and ductile failure modes of materials underwater, providing quantitative indicators for material selection in engineering projects such as underwater protective structures, subsea pipeline coverings, and dam impact-resistant panels.

[0028] The above description represents the preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above examples based on the technical essence of the present invention shall still fall within the protection scope of the present invention patent.

Claims

1. A device for underwater low-speed drop hammer impact testing, characterized in that, include: The drop hammer loading control subsystem includes a support frame and two liftable sliding rails; Repetitive low-speed impact loads used to provide controlled energy; The underwater environment simulation subsystem includes a sealed container and a boundary response contact module. The sealed container consists of a base and an open top plate, used to completely immerse the sample in water and maintain a saturated water pressure. The boundary response contact module includes a constraint plate and an electromagnetic induction unit. Each electromagnetic induction unit contains a energized coil and is connected to an iron constraint plate. When the sample contacts any side of the constraint plate, a closed loop is formed, and the loop conduction triggers the generation of a current signal. The multi-source signal synchronous acquisition subsystem includes an optical morphology measurement module and a boundary response contact module. The optical morphology measurement module is installed on the drop hammer loading control system, and the boundary response contact module is installed on the underwater environment simulation subsystem. During the impact process, the system acquires real-time data on the surface morphology changes of the sample and the boundary displacement response data of the sample. The intelligent control subsystem includes a computer and a data exchange, and is connected to the multi-source signal synchronous acquisition subsystem for signal transmission and data storage. The drop hammer loading subsystem, the underwater environment simulation subsystem, the multi-source signal synchronous acquisition subsystem, and the intelligent control subsystem are integrated on the same physical platform. The subsystem automatically collects the number of initial impacts, the number of destructive impacts, the energy consumption per unit mass of impact, and the ductility coefficient of the sample, and generates a test report.

2. The apparatus for underwater low-speed drop hammer impact testing according to claim 1, characterized in that, In the drop hammer loading control subsystem, the support frame consists of a sliding rail, a metal base plate, and a metal top plate. The two liftable vertical sliding rails are fixedly mounted on the metal base plate, and a rigid connection is formed between the two liftable vertical sliding rails and the metal top plate. The first liftable vertical sliding rail is equipped with an industrial camera as an optical topography measurement module, and the second liftable vertical sliding rail is equipped with an electromagnet as a drop hammer adsorption and release mechanism.

3. The apparatus for underwater low-speed drop hammer impact testing according to claim 2, characterized in that, The sliding track surface is marked with graduations for height positioning. Specifically, the height position of the track is digitally adjusted by operating the winch through the intelligent control subsystem.

4. The apparatus for underwater low-speed drop hammer impact testing according to claim 2, characterized in that, The drop hammer adsorption and release mechanism can be any one of an electromagnetic adsorption mechanism, a vacuum adsorption mechanism, or a mechanical clamping mechanism.

5. The apparatus for underwater low-speed drop hammer impact testing according to claim 2, characterized in that, The electromagnet on the second liftable vertical sliding track is used to attract and release the metal drop hammer; after the magnetic force is eliminated by power-off, the drop hammer falls freely; then, the second liftable vertical sliding track moves downward along the vertical path to retrieve the drop hammer, and then returns upward to the preset height to realize a continuous impact test cycle; the weight of the drop hammer can be changed according to the test requirements, and its cross-sectional size is adapted to the test sample and is less than or equal to the diameter of the cross-section of the test sample to ensure uniform transmission of impact load.

6. The apparatus for underwater low-speed drop hammer impact testing according to claim 1, characterized in that, In the underwater environment simulation subsystem, the base is made of welded metal, and the base is connected to the open top plate by bolts; The opening top plate is designed to be detachable for placing samples and injecting water; The center of the open top plate is also provided with a mounting hole that is adapted to the shape of the force dispersion structure; the force dispersion structure, which is placed directly above the sample, has a continuous curved surface on its lower surface, which is used to evenly distribute the impact load of the drop hammer to the top surface of the sample. The force-dispersing structure is any one of a spherical, ellipsoidal, frustum conical, or ring-shaped rigid body.

7. The apparatus for underwater low-speed drop hammer impact testing according to claim 1, characterized in that, In the multi-source signal synchronous acquisition subsystem, the optical topography measurement module is an industrial camera mounted on a camera bracket on the first liftable vertical sliding track of the drop hammer loading control subsystem. It is used to acquire the full-field surface displacement field and strain field of the sample during the impact process. It includes at least one boundary contact response module for monitoring the change in contact state between the sample and its surrounding constraint structure under impact. The specimen topography measurement module can be any one of a digital image correlation (DIC) system, a laser scanning vibrometer, or a structured light 3D reconstruction system. The boundary contact response module is a contact sensing unit based on the principles of electromagnetic induction, capacitance change, resistance switching, or optical blocking.

8. The apparatus for underwater low-speed drop hammer impact testing according to claim 1, characterized in that, The intelligent control subsystem is electrically connected to the multi-source signal synchronous acquisition subsystem, used to acquire, store, and analyze image data of the sample after being subjected to drop hammer impact; it can identify the moment when the sample first shows macroscopic damage based on the sample surface morphology change data and record the corresponding number of impacts; based on the sample boundary displacement response data, it can identify the moment when the sample undergoes critical plastic deformation and record the corresponding number of impacts; when the moment of plastic deformation is identified, the impact test process is automatically terminated, and a test report containing the number of impacts is output; the test report includes the number of initial crack impacts and the number of destructive impacts, or the energy consumption per unit mass of impact and the plastic deformation ductility coefficient.

9. The apparatus for underwater low-speed drop hammer impact testing according to claim 1, characterized in that, The sample can be any one of a cylinder, prism, or frustum, and its dimensions must satisfy the following: diameter or side length not less than 50 mm and not more than 200 mm, and height-to-diameter ratio between 1.5:1 and 3:

1.

10. The apparatus for underwater low-speed drop hammer impact testing according to claim 1, characterized in that, When the device performs a low-speed drop hammer impact underwater, the low-speed impact is defined as follows: the final velocity of the drop hammer does not exceed 5m / s, the impact energy is adjustable from 10J to 500J, and the duration of a single impact is greater than 10ms.

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