The area of vehicle occupant restraint systems comprises airbag systems (airbags) as well as belt tensioners and belt force limiters.
These systems are always activated by igniting pyrotechnic materials.
Some of the gases and dusts emitted are harmful to health and are subject to worldwide regulation. Although the emissions of the individual modules have fallen significantly over the past 20 years in terms of toxicity and quantity, this progress has been offset by the much higher number of systems now available in vehicles.
The measurement procedures and the evaluation of the results are defined in the ECE area by the more or less standard AK-ZV01 (target agreement of the german automotive industry) and internationally also by the automotive standard SAE J1794/USCAR.
Our procedure, which is accredited both according to AK-ZV01 and SAE J1794, allows gas, dust and acoustic emissions from pyrotechnic restraint systems to be determined and evaluated. The emission measurements can be carried out in a 60 litre can, a 2.7m³ tank or in a test vehicle provided by the customer. The results from the 2.7m³ tank can be converted to 2.5 m³ (AK-ZV01) and 100 ft³ (SAE/USCAR).
Standards: AK-ZV 01; SAE J1794; USCAR
The gases emitted by automotive pyrotechnics after ignition are analysed by an accredited GWP method according to AK-ZV01 or SAE J1794. The GWP method goes far beyond the procedure required by the standards:
Standards: AK-ZV 01; SAE J1794
In accordance with the AK-ZV01 and SAE J1794 standards, particles emitted after ignition of vehicle restraint systems must be characterized with regard to their mass and properties. In addition to the concentration of the total dust, the size distribution of the emitted particles, the proportion of respirable dust (PM10) and its chemical composition are essential here.
In the GWP process, the total dust is classified into nine sizes between < 0.4 µm and > 9 µm using an Andersen impactor. With a sufficient quantity (> 50 mg), the collected dust can then be examined for various chemical parameters (soluble fraction, pH value, heavy metals). At the customer's request, the morphology of the particles (modular or fibrous, possible quartz content) can also be examined electron microscopically.
Standards: AK-ZV 01; SAE J1794
The performance characteristics of gas generators can be investigated by ignition in a 28, 60 or 100 L chamber. The pressure curves in the chamber are recorded. It is also possible to follow the internal pressure curves of the gas generators by measuring through a drill hole in the generator itself. The resulting pressure profile describes the performance of the propellant in the applied environment.
The decisive parameter of propellants is the burning rate. This can be determined by igniting in a ballistic bomb. With a defined geometry of the propellants, the pressure-dependent burning rate and other important parameters can be determined from the pressure curve.
Since the pyrotechnical performance of propellants depends on the ambient temperature, the measurements can be carried out at different temperatures.
Standards: AK-ZV 01; SAE J1794
Airbag components consist of a wide variety of materials and are manufactured using a variety of joining processes. High quality is a basic requirement due to the stress during driving and ignition.
Materialography helps to qualify and verify the materials and joining processes used in the development and manufacture of airbag components. It is also indispensable for damage analyses and recalls. For example, phase determinations are carried out on the propellant tablets, weld seam evaluations on gas generators or target preparations on plug connections in order to characterize components or determine manufacturing or material defects.
In order to cope with the great variety of material-technical challenges of airbag components, GWP operates a well-equipped materialography. A wide range of methods and consumables is available for every requirement. In conjunction with other competencies such as scanning electron microscopy, analytics and materials testing, we can carry out comprehensive investigations to accompany developments and/or evaluate any damage that has occurred and ensure the needed quality.
Igniters are a tight packing of materials and manufacturing processes; according to our experience there are often complex connections in production, function & aging. The GWP is equipped with many necessary competences to carry out demanding material-scientific characterizations (including permission and qualification according to the German explosives regulations).
Manufacturing example: If new processes are introduced, e.g. for plugging ignition pills with pyrotechnics, then the resulting ignition mixtures (Zr, TiH2, chlorates, boron, nitrates) are analysed with regard to cracks, homogeneity, density, sedimentation, element distribution, etc. Close contact with the glow bridge - for instant ignition - is particularly important.
The test methods used are radiography, µ-CT, macroscopic cross-sections, ATR-FTIR, DSC, LIM, pycnometry and scanning electron microscopy with EDX analyses. For aging, we perform environmental simulations for temperature/humidity cycles according to AKLV, US standards and our own work regulations. The pyrotechnic performance is determined on a U,I,t test bench.
Our 20 years of experience, resulting from developments and recalls, shows that the following elements or functions of an ignition cap should be tested:
X-ray fluoroscopy of airbag modules in the form of 2D images or 3D CT scans provide you with non-destructive methods about the condition of gas generators or modules. In this way you can check the position or the presence of individual components such as the booster charge or the auto-ignition tablet. In addition, the dimensions of individual components can be determined.
After the ignition it also allows the documentation of the correct function of the mechanical elements of the inflators.
Determination of the strength and damage behavior of airbag fabric under various load conditions or in the event of damage are part of the GWP services.
We characterize the structure and material behavior of typical airbag fabrics made of polyamide 6.6 under various load conditions. Another important material parameter for the characterization of airbag fabrics is, for example, the silicone coating thickness and the melting behavior on contact with hot particles.
The failures caused by broken ignition wires in airbag igniters gave rise to the development of a method for determining the mechanical strength of exposed ignition wires and for characterizing their material properties.
GWP offers in this field:
The performance of pyrotechnic propellants and their ignition agents during combustion depends not only on the chemical composition but also sensitively on the physical properties. The GWP applies numerous methods to determine density (geometric, pycnometric), porosity by Hg porosimetry, thermal properties or residual moisture. On-site obtaining of the propellant from pyrotechnic articles of categories PT1 and PT2 is also possible.
Prove the quality and reliability of your airbag modules. We carry out the qualification of your gas generators and airbag modules by environmental simulation according to AK-LV. We offer vibration, shock and temperature shock tests, tests for electromagnetic compatibility and resistance to corrosion, dust, salt and moisture.
In addition to standardized tests, we also offer ultra-speeded up tests such as "Accelerated Temperature Cycling" (ATC) or similar methods for the rapid re-enactment of damage cases.
Climatic influences can influence the reliability of propellants over long periods of time.
We carry out specially developed environmental simulations on airbag propellants. Customer-specific artificial aging of airbag fuels contributes to the clarification of their long-term stability. By varying humidity and temperature under the influence of various other factors, meaningful results can be achieved.