NTS News Center

Latest News in Testing, Inspection and Certification

NTS News Center - Latest News in Testing, Inspection and Certification

NTS offers CAD/FEA Modeling for Direct and Indirect Effects Lightning, Reducing Test Costs and Time

The NTS Lightning Technologies laboratory in Pittsfield, MA is now offering finite element analysis, allowing the performance of complex simulations that accurately model the interaction of lightning with a variety of aircraft and avionics components for our customers. This service is available to all of the customers of the 10 NTS facilities across the US offering direct and indirect lightning testing.

Lightning Testing Figure 2

Figure 1 – Current Distribution and Magnetic Field in Two Current Carrying Copper Conductors

By decomposing complex CAD-generated objects into meshable geometrical shapes, these models are able to accurately portray the lightning environment (current distribution, electric and magnetic fields, pressure waves, temperature variations, induced transients) on high fidelity renditions of real objects. Once the geometry is built, highly customizable material parameters, boundary conditions, and applicable physics interfaces (Maxwell’s Equations) are applied that generate a system of equations that is solved in COMSOL. With accurate representation of test object geometries, the solutions of these models allow for conducted and induced transients to be determined at any point in the model.

Figure 2 - Magnetic Field Penetration through Apertures on a Fuselage

Figure 2 – Magnetic Field Penetration through Apertures on a Fuselage

Utilizing simulation and modeling along with laboratory testing provides customers with a new, cutting edge way to obtain valuable test data that can reduce testing costs substantially. Making use of these models allows for the easy acquisition of difficult or impossible to obtain lab measurements (equipment limitations) without having to perform the test on an actual object. Once a model has been developed, a similar test is performed on a real piece of equipment in order to validate the model. Once the model has been validated, lightning attachment locations, cable routing configurations, and material characteristics (to name a few) are all easily modifiable to allow for many permutations of the test environment to be modeled. The results of these models can provide valuable design constraints and necessary test levels for certification. Additionally, once validated, these models can serve as a firm basis for similarity analyses for future design changes, providing the potential for a cost and schedule reduction to future programs.

Figure 3 - Magnetically Induced Voltage on Conductor inside Fuselage

Figure 3 – Magnetically Induced Voltage on Conductor inside Fuselage

For questions about our new finite element modeling and how it can be applied to your testing program or for any other lightning test related inquiries please contact our General Manager Mike Dargi at 413.499.2135 or Mike.Dargi@nts.com

NTS has 10 facilities across the US capable of performing your complex direct effects and indirect effects lightning testing. We are able to meet the full scope of RTCA DO-160 testing, as well as numerous other specifications with lightning requirements including MIL-STD-461/462, SAE ARP 5416A, and IEC 61400-24 (wind turbines). Contact us today to discuss your next test program.

Explicit Finite Element Modeling Capability Enables Pyrotechnic Shock Test Design at NTS

For our customers in the space launch industry the requirement to perform pyrotechnic shock testing in the course of qualifying major subsystems and critical components of a space craft or payload is often a daunting prospect. This is due to the uncertainty associated with achieving specified shock levels (expressed in terms of an acceleration based shock response spectrum, or SRS) in traditional ordnance induced tests.

Historically, NTS and its competitors have performed iterative “equalization” tests using mass models of the product to be tested, or non-functional parts, to arrive at a test design that is acceptable to both the testing facility and the customer prior to running the shock test on the hardware to be qualified. This can involve significant expenditure of both test scheduling resources and consumption of test fixture hardware until a test design is agreed upon. There is also the resulting problem of significant over-testing across wide frequency ranges to insure the chances of an under-test are minimized.

Ordnance induced pyrotechnic shock testing is performed using a small explosive charge to impart an intense and very short (microseconds in duration) impulse to a resonating plate. The resonating plate responds to this impulsive load by propagating elastic stress waves (while some localized plastic deformation on the plate beneath the explosive charge does occur) throughout its volume which then reflects off free surfaces creating a very complex three dimensional transient stress field. It is this complex transient stress field that imparts the shock acceleration time history to the shelf or other test fixture structure acting as the interface between the resonating plate and the unit being tested as shown in Figure 1 below.


Figure 1. Response of Pyroshock Test Resonating Plate to Explosive Charge Detonation

For the last couple of years, the engineering services group at NTS Dana Point, CA, in partnership with our test facilities that perform pyrotechnic shock testing, has employed an explicit finite element solver, LS-DYNA, to perform design and analysis of pyrotechnic shock testing for various customers. This approach allows NTS to evaluate a wide range of pyrotechnic shock test fixture design options, explosive charge quantity and placement, in combination with basic mass properties models of the customer’s test article, without consuming any hardware resources.

Recently, this unique capability was recognized by the selection of the NTS paper, “Modeling of Ordnance-Induced Pyrotechnic Shock Testing,” for the Henry Pusey Award (best paper) at the 84th Shock & Vibration Symposium in Atlanta, GA in 2013.  As shown in Figure 2 below, excellent agreement has been achieved between the modeling and simulation results.

Pyro Shock Testing Comparison Model

Figure 2. Comparison of Explicit FEA Predicted SRS with Test Data

Although the commercially available explicit finite element solver, LS-DYNA, is a great resource for performing the required analyses, the key enabler of this capability has been the rapid evolution in computing power at the PC desktop workstation level. For the modeling approach to serve in the role as a functional replacement for performance of iterative equalization testing to evaluate a variety of test fixture design concepts and explosive charge size and placement, the turn-around time for performing each test fixture design iteration using the explicit finite element based modeling approach must be on the scale of 30 minutes or less of wall clock time. Run times on this scale for these models are now routinely achieved at our facility in Dana Point, CA. This approach also allows for a considerably wider range of test fixture design concepts to be evaluated without any risk to the customer furnished test hardware, as the additional cost and schedule associated with fabricating and assembling each test fixture design iteration is absent.

Explicit finite element modeling techniques have traditionally served in the role of weapons design codes for the US DOD and DOE. It is now being recognized that these same techniques have wider application to non-defense industries ranging from automotive and aircraft crash test analysis to safety barrier design and aerospace pyrotechnic shock testing design may now be added to this list.

NTS Dana Point specializes in engineering services to a range of industries in the defense and commercial sectors. More information can be found on the NTS Dana Point webpage, or by calling 949.429.8602.