In low temperature environment, the strength of steel structure increases while the toughness decreases, which is easy to cause brittle fracture. Traditional strain measurement methods such as strain gauges are expensive, easy to damage, and have limited measurement area.
Recently, researchers from the civil engineering laboratory of a key university introduced digital image correlation technology DIC and carried out a drop hammer impact steel pipe experiment based on a low-temperature and high-speed DIC measurement system. The purpose was to study the influence of low temperature on the strain distribution of steel structures and provide experimental data reference for the performance research of steel structures in extremely cold regions.
Experimental equipment
This experiment uses the high-speed DIC system independently developed by Qianyanlang. The core equipment includes:
1. High-speed camera, S1315M, has the industry benchmark parameter of 15,000 frames at 1280×1024 resolution, which can capture the transient details of high-speed impact.
2. 3D3C RDIC software, combined with the easy-to-use high-speed camera acquisition software RCC, post-processes the acquired images and efficiently analyzes the full-field displacement and strain data.
3. Drop hammer device, customized high-precision drop hammer device, hammer weight 50kg, maximum drop hammer height 3m, impact speed can reach 5m/s, providing the impact load required for the experiment.
4. Steel pipe specimen, cylindrical, 3m long, 20cm in diameter, observe the strain distribution and deflection change in the impact area.
Other supporting equipment include low-temperature speckle paint preparation specimens, 28mm spacing high-precision calibration plates, high-power light source systems, etc.
Experimental procedures
1. Prepare the surface speckle of the specimens in the normal temperature group and the low temperature group. The low temperature uses a special speckle paint of -30°C. The steel pipe specimen is fixed on the impact table, and the 28mm spacing dot plate is calibrated to complete the three-dimensional spatial positioning.
2. The critical drop height of the normal temperature group was determined through preliminary experiments. After the specimens of the low temperature group were cooled in a -30°C environment, they were impacted at the same height, and the 3D high-speed DIC measurement system was started simultaneously to collect experimental data.
3. Use the Qianyanlang 3D DIC measurement software to post-process the data and compare and analyze the strain of the specimens at room temperature and low temperature.
Experimental data and conclusions
The Thousand Eye Wolf 3D high-speed DIC measurement system records the transient process of the drop hammer impacting the steel pipe in real time at a shooting frame rate of 15,000 frames per second. After being processed by the DIC measurement software:
1. The peak strain value of the column foot in the low temperature group increased by 45% compared with that in the normal temperature group, and the strain value of the measuring point on the windward side of the column was significantly higher than that on the leeward side, with an increase of 52%, indicating that the environmental coupling effect aggravates the local stress concentration .
2. According to DIC calculation, the maximum deflection of the steel pipe under impact is 8.3mm, which is only 1% different from the laser distance measurement result. This verifies the high accuracy of the DIC system measurement.
The success of the drop hammer impact test in a low temperature environment provides valuable data and reliable methods for further studying the performance of steel structures at low temperatures. The subsequent research team will conduct in-depth research on the impact resistance of various types of steel structures and other composite materials. Qianyanlang will be committed to the research and development of advanced DIC strain measurement systems to provide accurate, efficient and easy- to-use DIC measurement solutions for scientific research and engineering fields.
Attached Qianyanlang 3D high-speed DIC measurement system
Qianyanlang RDIC-3D three-dimensional full-field high-speed strain measurement system consists of two Qianyanlang high-speed cameras, synchronous triggers, measurement software, calibration plates, and a graphics workstation. It supports instantaneous measurement of the spatial three-dimensional coordinates of objects, displacement and strain data under extreme impact loads, etc.
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