Nanoindentation tester is a high-precision material mechanical property testing instrument, and its use must strictly follow the operating specifications to ensure data accuracy and instrument stability. The following are details about the use of nanoindentation instruments, covering the entire process from preparation to data analysis.
1、 Preliminary preparation work
1. Instrument inspection and environmental preparation
-Confirm that the instrument power supply and gas source (if necessary) are connected properly, and check whether the pressure head, stage, microscope and other components are clean and undamaged.
-Place the instrument on a stable workbench to avoid external vibration interference. It is recommended to wear protective goggles to prevent splashing injuries.
-Before starting up, it is necessary to preheat the instrument to the set temperature (usually 30 minutes to 1 hour), especially for piezoelectric ceramic or coil systems, to ensure stable performance.
2. Sample preparation and installation
-The sample needs to be cut to a suitable size (such as 10 mm × 10 mm), polished to a mirror effect on the surface, and cleaned by ultrasonic cleaning to remove contaminants.
-Use specialized fixtures to fix the sample, ensuring that the surface is perpendicular to the indenter and avoiding tilting that may cause abnormal indentation morphology
2、 Parameter setting and calibration
1. Selection and calibration of pressure head
-Select the type of indenter according to the testing requirements (such as Belleville indenter, triangular cone indenter), and check the tip radius and wear condition of the indenter.
-Use a standard hardness block (such as fused silica) to calibrate the indenter, obtain the load displacement curve through multiple indentations, calculate the actual contact area and hardness value, and correct the system error.
2. Experimental parameter setting
-Set parameters such as maximum load (e.g. 100 μ N-10 mN), indentation depth (e.g. 100 nm-5 μ m), loading rate (e.g. 0.5 mN/s), etc., and adjust them according to the material hardness to avoid overloading and damaging the indenter or sample.
-Define the load hold unload program (such as trapezoidal load mode) and set the data sampling frequency (usually ≥ 1 kHz).
3、 Test operation process
1. Indentation test
-After starting the program, control the pressure head to slowly approach the surface of the sample and adjust it to the contact state (zero calibration).
-Load the load according to the set program, monitor the load displacement curve in real time, and observe the stages of elastic deformation and plastic deformation.
-After uninstallation, it is necessary to wait for a period of time (such as 30 seconds) to eliminate the influence of thermal drift before proceeding with the next indentation.
2. Multi point measurement and repeatability control
-The same sample needs to be subjected to multiple indentation tests (usually ≥ 5 times), and the average value should be taken to improve data reliability.
-Avoid the indentation distance being too close (recommended ≥ 10 times the indentation depth) to prevent errors caused by stress field superposition.
4、 Data Processing and Analysis
1. Load displacement curve processing
-Record the loading and unloading curves, calculate the contact stiffness by fitting the slope (S) of the unloading section, and calculate the hardness by combining the maximum load (P_max) and contact depth (h3):
\\[H=\ \ frac {P_ {\ \ text {max}} {A} \ \ quad \ \ text {where} \ \ quad A=f (h3) \ \]
In the formula, A is the projected area of the indentation, determined by polynomial fitting of the geometric shape of the indenter.
-The elastic modulus is calculated using the rugby model and requires input of material parameters such as Poisson's ratio.
2. Error sources and corrections
-Common errors include thermal drift, head wear, sample surface roughness, etc., which need to be corrected through calibration and blank experiments.
-For soft materials or films, a substrate effect correction model (such as the King model) should be used.
5、 Instrument maintenance and precautions
1. Daily maintenance
-Clean the pressure head and sample stage after testing to avoid residual particles affecting subsequent experiments.
-Regularly check the sharpness of the indenter, and replace or recalibrate if it is severely worn.
-Cover with a dust cover during storage to prevent mold growth of optical components in humid environments.
2. Operating standards
-Avoid frequent switching of loading directions to prevent piezoelectric ceramics from overheating and failure.
-Overloading operation is strictly prohibited, and the indentation depth generally does not exceed 10 times the radius of the indenter.
-Data needs to be saved in real-time, and the instrument status should be checked and recalibrated in a timely manner in case of sudden power outages.