What is the parameter of vibration test?

Vibration testing is a dynamic and multifaceted discipline, and its effectiveness hinges on precisely defining and controlling various parameters. At Dongguan Precision Test Equipment Co., Ltd., we understand that successful vibration testing isn't just about "shaking" a product; it's about executing a highly controlled and quantifiable process. Understanding these parameters is crucial for setting up meaningful tests, interpreting results, and ensuring product reliability.

Here's a breakdown of the key parameters used in vibration testing:

1. Frequency (Hz):

• Definition: Frequency (f) is the most fundamental parameter in vibration testing. It measures the number of complete cycles or oscillations that occur per second. The unit is Hertz (Hz).

• Significance: Frequency is critical because products often have resonant frequencies – specific frequencies at which they naturally tend to vibrate with much larger amplitudes. If operational or transportation vibrations match these resonant frequencies, it can lead to catastrophic failure.

• Application: In sinusoidal vibration, frequency is often swept across a range to identify resonances. In random vibration, a broad spectrum of frequencies is excited simultaneously.

2. Amplitude (Displacement, Velocity, Acceleration):

Amplitude describes the severity or intensity of the vibration. It can be quantified in three related ways, each emphasizing different aspects of the motion:

• Displacement (D):

  • Definition: Measures the distance a vibrating object moves from its equilibrium (resting) position. It's typically expressed in millimeters (mm) or inches.

  • Significance: Most sensitive to low frequencies. It's crucial for understanding the "swing" or overall movement of large components or structures, and for ensuring mechanical clearances. For example, excessive displacement can indicate unbalance or misalignment in rotating machinery.

• Velocity (V):

  • Definition: Measures the rate of change of displacement over time – essentially, how fast the object is moving during its oscillation. It's expressed in meters per second (m/s) or inches per second (in/s or ips).

  • Significance: Often considered the "happy medium" as it is sensitive across a broad range of frequencies (mid-frequency range). Velocity is directly related to the energy of the vibration and, consequently, the potential for fatigue damage in components. It's widely used for general machinery health monitoring.

• Acceleration (A):

  • Definition: Measures the rate of change of velocity over time – how quickly the movement picks up or loses speed. It's expressed in meters per second squared (m/s²) or, more commonly, in G-forces (g), where 1g is the acceleration due to Earth's gravity (approx. 9.81 m/s²).

  • Significance: Most sensitive to high frequencies. Acceleration is particularly important for detecting impact-related events, high-frequency defects like bearing faults or gear teeth issues, and the dynamic forces acting on electronic components. It directly relates to the forces exerted on a product.

  • Relationship: These three parameters are mathematically interrelated. For sinusoidal motion, knowing any one (along with frequency) allows you to calculate the other two. For example, A = (2πf)² × D (where D is half amplitude).

3. Test Duration:

• Definition: The total length of time the vibration test is conducted.

• Significance: Directly impacts the amount of stress and fatigue accumulated by the test specimen. Short durations might be used for functional checks, while long durations (hours or even days per axis) are common for accelerated life testing or fatigue studies to simulate years of real-world exposure.

4. Test Profile/Waveform:

This defines the specific nature of the vibration input:

• Sinusoidal (Sine): A single-frequency, predictable oscillation. Parameters include frequency range (for sweeps), dwell frequencies, and amplitudes (displacement, velocity, or acceleration).

• Random: A complex, broadband vibration where all frequencies within a specified range are excited simultaneously. Parameters include:

  • Power Spectral Density (PSD): A graph showing the distribution of vibration energy (typically acceleration squared per Hz, e.g., g²/Hz) across the frequency spectrum. This is the defining parameter for a random vibration test.

  • RMS (Root Mean Square) Acceleration: A statistical measure of the overall energy or severity of the random vibration, calculated from the PSD.

• Shock: A sudden, transient impact or impulse. Parameters include:

  • Pulse Shape: The characteristic shape of the acceleration pulse over time (e.g., half-sine, sawtooth, trapezoidal).

  • Peak Acceleration (G-level): The maximum instantaneous acceleration reached during the pulse.

  • Pulse Duration: The length of time the shock event lasts (in milliseconds).

  • Number of Shocks: The total number of pulses applied.

5. Axes of Vibration:

• Definition: The directions in which vibration is applied to the product.

• Significance: Products are often subjected to multi-directional vibrations in real-world scenarios. Testing is typically performed sequentially along the three orthogonal axes (X, Y, Z) to ensure all critical directions are stressed. For complex scenarios, multi-axis simultaneous testing is also employed.

6. Temperature and Humidity (Environmental Factors):

• Definition: While not direct vibration parameters, ambient temperature and humidity levels are critical environmental factors during vibration testing.

• Significance: Temperature can significantly affect material properties (e.g., stiffness, ductility) and component performance. Vibration is often combined with thermal cycling or extreme temperatures in an environmental chamber to simulate real-world conditions more accurately (e.g., Combined Environmental Testing).

At Dongguan Precision, our state-of-the-art vibration test systems allow you to precisely control and monitor all these critical parameters. By mastering these variables, you can conduct robust vibration tests that yield invaluable data for product design, quality assurance, and compliance, ultimately leading to more reliable and durable products for your customers