How to select testing equipment according to GJB150A standard-Shock Test

How to select testing equipment according to GJB150A standard-Shock Test

MIL-STD-810H&GJB150A

MIL-STD-810H and GJB150A are standards for testing the environmental adaptability and durability of equipment. MIL-STD-810H is a U.S. military standard primarily used to test the reliability and adaptability of equipment under various extreme environmental conditions, such as high and low temperatures, humidity, vibration, and shock. It is widely used for various U.S. military equipment, including communication devices, vehicles, and weapons.

GJB150A is China’s military equipment environmental testing standard, which is similar to MIL-STD-810H and is used for testing the environmental adaptability of military equipment. It covers test items such as temperature and humidity, vibration, sand and dust, and corrosion, ensuring that equipment can function properly in complex environments.

Shock tests are primarily encompassed within the standards MIL-STD-810H Method 516.8 and GJB150A.18A.

Purpose and Application

a)      Provide a degree of confidence that materiel can physically and functionally withstand the shocks encountered in handling, transportation, and service environments. This may include an assessment of the overall materiel system integrity for safety purposes in any one or all of the handling, transportation, and service environments.

b)      Determine the materiel's fragility level, in order that packaging, stowage, or mounting configurations may be designed to protect the materiel's physical and functional integrity.

c)       Test the strength of devices that attach materiel to platforms that may be involved in a crash situation and verify that the material itself does not create a hazard or that parts of the materiel are not ejected during a crash situation.

Use this Method to evaluate the physical and functional performance of materiel likely to be exposed to mechanically induced shocks in its lifetime. Such mechanical shock environments are generally limited to a frequency range not to exceed 10,000Hz, and a duration of not more than 1.0 second. (In most cases of mechanical shock, the significant materiel response frequencies will not exceed 4,000Hz, and the duration of materiel response will not exceed 0.1 second.)

Shock Response Spectrum

If measured data is not available, the SRS and the corresponding values of T_e and T_E may be derived from (1) a carefully scaled measurement of a dynamically similar environment, (2) structural analysis or other prediction methods, or (3) from a combination of sources. For Procedure I (Functional Shock with Terminal Peak Sawtooth Reference Criteria), and Procedure V (Crash Hazard Shock), employ the applicable SRS spectrum from Figure 1 as the test spectrum for each axis, provided T_e and T_E of the test shock time history is in compliance with the accompanying Table 1. This spectrum approximates that of the perfect terminal-peak sawtooth pulse. General guidance for selecting the crossover frequency, F_co , for any classical pulse is to define it as the lowest frequency at which the corresponding SRS magnitude reaches the convergence magnitude (the constant magnitude reached in the high frequency portion of the SRS) for the damping ratio of interest. Once F_co is defined, the effective duration considered in the complex pulse synthesis is then defined as T_E≤ 2/ F_co. This guidance allows for a longer effective duration than previous versions of this standard that were found to be too restrictive.

It is recommend that the test be performed with a waveform that is synthesized from either (1) a superposition of damped sinusoids with selected properties at designated frequencies, or (2) a superposition of various amplitude modulated sine waves with selected properties at designated frequencies, such that this waveform has an SRS that approximates the SRS on Figure 1. In reality, any complex test transient with major energy in the initial portion of the time trace is suitable if it is within tolerance of this spectrum requirement over the minimum frequency range of 10 to 2000Hz, and meets the duration requirements. Implementing a classical terminal-peak sawtooth pulse or trapezoidal pulse on a vibration exciter are the least permissible test alternatives. In the case in which a classical pulse is given as the reference criteria, it is permissible to synthesize a complex pulse based on the SRS characteristics of the referenced classical pulse. In such cases, T_e and T_E should be defined as in Table 1.

Figure 1 Test SRS for use if measured data are not available (for Procedure I Functional Shock, and Procedure V Crash Hazard Shock)

Table 1 Test shock response spectra for use if measured data are not available

Classical Shock Pulse

Classical shock pulses (e.g., half-sine, terminal peak sawtooth, or trapezoidal) may be defined by (1) time history measurements of the materiel’s environment, (2) from a carefully scaled measurement of a dynamically similar environment, (3) from structural analysis or other prediction methods, or (4) from a combination of sources. The terminal peak sawtooth is often referenced due to its relatively flat spectral characteristics in the SRS domain as approximated in Figure 1. In the event that a-priori information regarding rise time of the transient event being considered is determined to be a critical parameter, consider a half-sine pulse or a trapezoidal pulse with a tailored rising edge in lieu of the terminal peak sawtooth. Shock pulse substitution (e.g., half-sine in lieu of terminal peak sawtooth) requires adjustment in the amplitude such that the velocity of the substituted shock pulse is equivalent to the original specification. The resulting over-test or under-test with respect to the difference in the SRS must be considered, documented, and approved by the appropriate testing authority. If a classical shock pulse is defined in lieu of more complex measured time history data it must be demonstrated that SRS estimates of the classical shock pulse are within the tolerances established for the SRS estimates of the measured time history data. In most cases, classical shock pulses will be defined as one of the following:

a)      Terminal Peak Sawtooth Pulse: The terminal peak sawtooth pulse along with its parameters and tolerances are provided in Figure 2 and is an alternative for testing in Procedure I Functional Shock, Procedure II Transportation Shock and Procedure V Crash Hazard Shock Test.  

b)   Trapezoidal Shock Pulse: The trapezoidal pulse along with its parameters and tolerances is provided in Figure 3. The trapezoidal pulse is specified for Procedure III Fragility.  

c)       Half-Sine Shock Pulse: The half-sine pulse along with its parameters and tolerances is provided in Figure 4. The Half-Sine Pulse is specified for Procedure I High Speed Craft Functional Shock.

Figure 2 Terminal peak sawtooth shock pulse configuration and its tolerance limits

Table 2 Terminal peak sawtooth default test parameters (refer to Figure 2)

Figure 3 Trapezoidal shock pulse configuration and tolerance limits

Table 3 Trapezoidal pulse parameters (refer to Figure 3)

Recommended equipment

KRD14 Pneumatic Vertical Shock Response Spectrum Test System

KRD14 series shock response spectrum tester is used to measure and determine the shock resistance of electrical and electronic products or packaging, and to evaluate the reliability and structural integrity of the test product in a shock environment. The shock response spectrum is the total result of a series of single-degree-of-freedom linear systems with different natural frequencies subjected to the same shock excitation response. When a product is subjected to an impact, the maximum value of its impact response means that the product has a maximum stress. Therefore, the shock response spectrum tester can better simulate the shock wave and shock energy suffered in the real environment.

KRD15 Pneumatic Horizontal Shock Response Spectrum Test System

KRD15 series is the state-of-the-art shock response spectrum tester that adopts compressed gas energy to provide impact energy, push the shock hammer to impact the resonance plate, and generate high energy shock. Comparing to traditional pendulum shock response spectrum tester, this machine has the advantages of high energy, stable performance, high reliability, good repeatability, easy adjustment, safety and environmental protection. It is mainly applied in the industries of aerospace, aviation and ships.

KRD11 Pneumatic Vertical Shock Test System

KRD12 Pneumatic Horizontal Shock Test System

KRD12 series shock test system is used to measure and determine the horizontal impact resistance of a product or package, and to evaluate the reliability and structural integrity of the test unit in a horizontal impact environment. The system can perform conventional half-sine wave, post-peak sawtooth wave, or trapezoid wave shock test to realize the shock energy that the product is subjected to in the actual environment, thereby improving the product or packaging structure.

KRD13 High Energy Shock Test System

KRD13 series high energy shock test system is specially designed to meet the requirements of military industry and home appliances. The system adopts the principle of pneumatic energy storage expansion. By adjusting the inflation pressure, various high-level acceleration tests can be easily implemented in a short stroke.