As the core equipment for testing the mechanical properties of materials, the stability of material testing machines directly affects the reliability of test data. The following systematically analyzes common fault phenomena, causes, and solutions from five dimensions: mechanical system, sensor system, control system, software system, and environmental factors, and provides preventive maintenance recommendations.
1、 Mechanical system malfunction
1. Abnormal loading mechanism
-Phenomenon: Stump, abnormal noise or sudden load changes occur during the loading process
-Cause: Insufficient lubrication of the guide rail leads to metal friction; The clearance between the lead screws is too large; The transmission belt is aging and loose
-Solution:
-After stopping the machine, use a special wrench to check the fastening screws of the guide rail and apply molybdenum disulfide grease
-Adjust the clearance between the screw nut to the range of 0.05-0.1mm
-Replace the polyurethane synchronous belt (with tension controlled at 3-5N · m)
-Prevention: Perform monthly lubrication and maintenance of mechanical components, and inspect the transmission system quarterly
2. Fixture failure
-Phenomenon: Sample slippage or abnormal fracture position
-Cause: Insufficient hardness of the fixture leading to plastic deformation; The wear of the wedge-shaped clamping block exceeds 0.1mm
-Solution:
-Using 40Cr steel fixtures and quenching treatment (HRC ≥ 55)
-Measure the parallelism of the clamping surface using a micrometer, and grind and repair it if it exceeds the tolerance
-Innovative method: Laser cladding repair fixture surface, extending service life by more than 3 times
2、 Sensor system malfunction
1. Inaccurate load sensor
-Phenomenon: Zero drift>1% FS or linear error exceeding the standard
-Cause: Elastic fatigue deformation; Wheatstone bridge imbalance; electromagnetic interference
-Solution:
-Perform three-point calibration method (0%, 40%, 100% full-scale)
-Check the integrity of the shielding layer, with a single ended grounding resistance of less than 4 Ω
-Replace the sensor affected by lateral force (choose spoke structure)
-Technical upgrade: adopting digital compensation sensor, temperature drift coefficient<0.01%/℃
2. Abnormal extensometer
-Phenomenon: Strain curve burrs or sudden range changes
-Cause: Blade wear (Ra>0.8 μ m); Flexible hinge fatigue
-Solution:
-Use diamond spray to polish the knife edge (roughness up to Ra0.2 μ m)
-Calibrate the gauge length using laser diffraction method (error<± 1 μ m)
-New solution: Non contact laser extensometer, eliminating the influence of mechanical contact
3、 Control system malfunction
1. Servo system oscillation
-Phenomenon: Periodic fluctuations in loading curve, delayed instruction response
-Cause: Excessive gain in the speed loop; Encoder feedback pulse loss
-Solution:
-Perform PID parameter self-tuning (typical values: Kp=1.2, Ki=20, Kd=0.05)
-Replace with a 17 bit absolute encoder (with a resolution of 0.001 °)
-Optimization design: Introducing fuzzy control algorithm to suppress mechanical resonance
2. Abnormal data collection
-Phenomenon: Sudden decrease in sampling frequency or data loss
-Cause: Poor contact of PCI bus; Collection card cache overflow
-Solution:
-Re insert the collection card and clean the gold finger (using anhydrous ethanol)
-Set the sampling frequency to within 80% of the nominal value of the device
-Hardware upgrade: Adopting FPGA architecture acquisition system, dead time<1 μ s
4、 Software system malfunction
1. Experimental curve distortion
-Phenomenon: Abnormal slope of elastic segment or misjudgment of yield point
-Cause: Improper setting of filtering parameters (cut-off frequency>5Hz)
-Solution:
-Enable anti aliasing filter (cut-off frequency set to 1/5 of sampling frequency)
-Manually adjust the yield point determination threshold (recommended 5% -10% offset)
-Intelligent improvement: Applying wavelet transform for noise reduction, improving signal-to-noise ratio by 20dB
2. Communication interruption
-Phenomenon: Control instructions cannot be issued or data transmission is interrupted
-Cause: Incompatible USB driver version; Network protocol conflict
-Solution:
-Install NI-VISA 5.2 or above drivers
-Unified Modbus RTU communication parameters (9600,8, N, 1)
-Remote diagnosis: Establishing a device digital twin through VPN to achieve cloud debugging
5、 Environmental impact factors
1. Temperature and humidity interference
-Phenomenon: Zero drift intensifies during continuous testing
-Cause: Laboratory temperature difference>2 ℃/h; relative humidity>80%
-Solution:
-Install a constant temperature and humidity unit (temperature fluctuation<± 1 ℃/4h)
-Configure automatic dehumidification device (dew point temperature ≤ 3 ℃)
-Environmental monitoring: Deploy IoT sensors and upload real-time environmental parameters
2. Electromagnetic interference
-Phenomenon: Periodic noise appears in the displacement signal
-Cause: High frequency harmonics (10kHz-100kHz) generated by nearby frequency conversion equipment
-Solution:
-Laying copper foil grounding grid (grounding resistance<4 Ω)
-The signal line adopts twisted pair shielded cable (shielded layer single end grounded)
-EMC design: The entire machine has passed the GB/T 17626-2017 Level 3 electromagnetic compatibility test
6、 Preventive maintenance system
1. Daily inspection: Check the status of the emergency stop button and limit switch; Clean the dust cover of the guide rail
2. Weekly inspection: Verify the zero point of the sensor; Check the lubricating oil level
3. Monthly inspection: Test the insulation resistance of the system (>50M Ω); Backup the experimental database
4. Annual inspection: Entrust the metrology institute to calibrate the entire machine (error<0.5%)