As the core equipment for testing the mechanical properties of materials, the operational standardization of the dynamic and static universal testing machine directly affects the reliability of test data and the service life of the equipment. However, in practical use, many users often fall into the following typical misconceptions due to cognitive biases or improper operating habits:

1、 Omissions in the installation and calibration process

1. Neglecting basic level calibration

Some operators believe that as long as the equipment is fixed, the levelness of the foundation is not strictly verified. In fact, if the host base tilts more than 0.5 °, it will cause the direction of force on the sensor to deviate from the axial direction, resulting in additional bending moments and a deviation of 3% -8% in the measured elastic modulus. The correct approach is to use a frame level to measure multiple points on the workbench, adjust the anchor bolts to the center of the bubbles, and perform software zero calibration before loading the specimen.

2. Misjudgment of fixture matching

Common errors include: ① selecting a jaw width smaller than the diameter of the specimen, resulting in local stress concentration; ② Using ordinary carbon steel fixtures to test high-strength materials such as titanium alloys can cause slippage on the mating surface; ③ The hydraulic fixture did not adjust the clamping pressure according to the yield strength of the material. For example, a certain university once had a sample detachment accident during the stretching of carbon fiber composite materials due to insufficient clamping force, directly damaging the extensometer. It is recommended to establish a fixture material adaptation matrix based on the GB/T 16491 standard and regularly check the wear of the clamping teeth.

2、 Logical trap of parameter setting

1. Improper setting of dynamic frequency

In high-frequency vibration tests, blindly pursuing high frequencies (>50Hz) can lead to resonance risks. A certain automobile manufacturer once set the excitation frequency to 80Hz during chassis suspension fatigue testing, which far exceeded the natural frequency of the component (about 35Hz), resulting in the fracture of the actuator connecting rod. A reasonable strategy is to follow the principle of 'displacement at low frequencies and acceleration at high frequencies' based on the characteristics of DDS digital servo technology, and determine the safe range through frequency sweep pre testing.

2. The protection threshold is virtually non-existent

Many users set the overload protection value to 120% of the theoretical maximum load, without considering the impact of temperature drift. In the high temperature environment of summer, the failure of oil source temperature control will cause a sudden increase in system pressure, and at this time, the original protection threshold cannot trigger the emergency stop in a timely manner. It is recommended to adopt a dual level protection mechanism: the first level warning is set at 90% of the full range, the second level hard limit is set at 110%, and the protection response time needs to be verified with standard weights every month.

3、 Cognitive blind spots in sample preparation

1. Loose control of geometric dimensions

A certain quality inspection agency once compared the same batch of aluminum alloy sheets and found that the tensile strength measured by different laboratories differed by 15%. Tracing back, it was found that the problem lies in the difference in the processing of the shoulder transition fillet of the sample - the stress concentration factor corresponding to R=2mm and R=5mm is nearly twice as high. The machining tolerance (± 0.05mm) specified in ISO 6892-1 must be strictly followed, and manual sanding with sandpaper is prohibited.

2. Misalignment of surface treatment process

For polymer materials, there are residual stresses inside the injection molded sample without annealing treatment, and direct testing will result in false high toughness values. The correct process should be to keep the material at the glass transition temperature Tg+20 ℃ for 2 hours in a constant temperature chamber, and then conduct the test after cooling in the furnace. For metal samples, attention should be paid to the thickness of the electroplating layer. If it exceeds 0.1mm, the coating mass should be deducted to calculate the true cross-sectional area.

4、 Behavioral deviation during the operation process

1. Violations during the cold start phase

When the winter ambient temperature is below 5 ℃, immediately running at full load will cause the hydraulic oil viscosity to be too high, exacerbating the wear of the pump unit. According to statistics from a special inspection institute, 70% of initial failures are caused by the failure to execute preheating procedures. The standard practice is to first start the circulating heating system, wait for the oil temperature to rise to 40-45 ℃, run it without load for 10 minutes, and then gradually increase the pressure.

2. Incorrect timing of human intervention

During low cycle fatigue testing, some operators may pause equipment observation during the crack initiation stage, which can alter the strain hardening process of the material. A study has shown that interrupting more than 5 times can increase fatigue life by 10% -15%, seriously interfering with the authenticity of raw data. Video surveillance should be enabled throughout the entire process, and if necessary, transparent explosion-proof covers should be used to isolate the operating area.

5、 Formal tendency towards maintenance and upkeep

1. Lack of maintenance for key components

The lubrication cycle of ball screw pairs is often misunderstood as' once every six months', but in fact, it should be dynamically adjusted according to the daily operating hours. A certain wind power enterprise operated for 16 hours every day for three consecutive months, but did not shorten the maintenance interval, ultimately resulting in the nut getting stuck. It is recommended to establish an intelligent reminder system based on working hours, replenish lithium based grease every 500 hours, and remove old grease before oil injection.

2. Failure of environmental control system

Many laboratories only focus on dust prevention of the host, ignoring the impact of temperature and humidity fluctuations. When the relative humidity is greater than 85% RH, the circuit board is prone to leakage; A temperature difference greater than 5 ℃/h will result in zero drift of the sensor. The best practice is to install precision air conditioning in the computer room, maintain a temperature of 20 ± 2 ℃ and a humidity of 50 ± 5% RH, and install a dehumidification transformer cabinet.

6、 The limitations of thinking in data processing

1. Rough removal of abnormal data

In the face of suddenly increasing noise signals, simply deleting suspicious data points may mask real defects. In the cable and steel wire test of a certain bridge, the peak value that appeared at the 37th second was originally a normal discrete fluctuation, but it was mistakenly deleted, resulting in a 12% lower calculation of the fatigue limit. Grubbs criteria should be used for statistical discrimination to preserve valid information.

2. Lack of multi physics field coupling analysis

In high-temperature creep tests, simply recording mechanical parameters without monitoring microstructural evolution is like a blind man feeling an elephant. In the study of blade materials for a certain aircraft engine, although accurate persistent strength data was obtained, the fundamental cause of premature failure was not revealed due to the lack of synchronous observation of grain boundary slip phenomenon. Modern experiments should integrate in-situ observation techniques and construct macroscopic microscopic correlation models.