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 lighting 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.

PyroTesting_Figure1

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.

Solar Radiation Testing in Accordance with Method 505 of MIL-STD-810

MIL-STD-810 Procedure 2 Solar TestingSolar radiation (sunshine) testing is one of the basic tests required for any military equipment planned to be deployed in the open and therefore subject to direct radiation from the solar source. The effects of this radiant energy can generally be divided into two groups or classes, heat effects and photochemical effects. Heat effects on exposed equipment can raise the internal temperatures of the equipment substantially above the ambient air temperature. Temperatures in excess of 160oF have been recorded in parked aircraft exposed to the sun while ambient air temperature was in the 90oF range. Photochemical effects of sunlight may hasten the fading of colors and lead to the deterioration of plastics, paints, rubber and fabrics. The combined effects may lead to the outgassing of plasticizers in some materials along with discoloration and a reduction in transparency.

MIL-STD-810, Method 505.5 outlines two procedures for performing the Solar Radiation test. Procedure I requires a cyclic exposure based on the diurnal cycle and is most useful for determining heating effects on exposed materiel as well as materiel enclosed within a container. Procedure II is a steady state (non-cyclic) exposure most useful for evaluating actinic (photochemical) effects of ultraviolet radiation on materiel since it represents an accelerated test with a factor of 2.5. Because Procedure I is more akin to a natural cycle and does not have the acceleration factor of Procedure II, it is not an efficient cycle with which to evaluate long term exposures. Therefore, when it is used mainly to evaluate the direct heating effect, Procedure I can be performed with source lamp arrays emitting less than the full solar spectrum. Procedure II however, demands full spectrum sources emitting light in the ultraviolet range if the total effects of long term exposure are to be properly evaluated.

The solar light spectrum has been accurately measured over the wavelength range of 280 – 3000 nm as well as the power distribution within this range, and it is this range that we would seek to reproduce in the Solar Radiation test.  Reproducing this entire range using lamp sources however can be quite challenging. Sources emitting ultraviolet wavelengths between 280 and 400 nm tend to be quite costly and their performance deteriorates quickly. Some of the MIL-STD recommended sources such as xenon arc and carbon arc fall into this category.  In fact, it was reported that the first commissioned sunshine test facility in 1945 fell short of the contract requirements due to several deficiencies, one of which was the amount of UV that could be produced at the test item. Cost and reliability issues are why many test labs have chosen to perform only Procedure I  with source lamps covering the visible and infrared spectrum range of 400 – 3000 nm (0.4 – 3.0 µm).

Reproduction of the required environment for the Solar Radiation test requires a chamber space in which the ambient air temperature and airflow over the test item can be controlled as well as a solar light source which may consist of a single source in the case of arc-type lamps or a multiple source array in the case of metal halide or incandescent type lamps. The distance of the light source from the test item may be varied to achieve the required irradiance. Airflow over the test item can significantly impact test results. When MIL-STD-810D introduced the “cycling for heat effects” (Procedure I) the guidance for airflow was to use airflow as low as possible consistent with achieving satisfactory control of the ambient air temperature at the test item or between 0.25 and 1.5 m/s (50 to 300 ft/min). The current guidance from MIL-STD-810G has changed for procedure I to 1.5 to 3.0 m/s (300 to 600 ft/min) in recognition of better field data. The requirement for peak radiation intensity at 1120 W/m2 has changed little over the history of the Solar Radiation test although there have been slight changes to the spectral energy distribution based on updated measurement techniques of the actual solar source.

When the primary concern is testing for heat effects, the question is often asked why an oven or chamber test for enclosed equipment could not be used in place of the Solar Radiation test.  The primary reason is that ovens and chambers transfer heat from a uniform ambient atmosphere surrounding the test item, whereas the solar test transfers heat through direct radiation. The directional effect of radiant heating produces temperature gradients through the test item that are not replicated in ovens or temperature chambers.

When a Solar Radiation test is required,

  • Perform the Solar Radiation test prior to the High Temperature test, as the product temperature measured in the solar chamber may need to be used as the ultimate high operating temperature for the product.
  • Consider the orientation of the test item within the solar chamber so as to replicate the in-use conditions with respect to both the direct radiant light energy and the airflow direction. This will affect both the temperature gradients and any cooling effects provided by the airflow.
  • When testing to Procedure I, remember that several consecutive cycles will likely be required for the product to achieve the ultimate high operating temperature for the most critical area of the test item to be within 2oC of the previous cycle. This usually means 3 to 7 cycles.
  • If operation of the test item is required, operational times will need to coincide with the peak response temperature of the test item in each cycle which will not coincide with the peak radiation intensity.

Scanning Electron Microscopy (SEM) Capability Expansion at NTS

SEM - Close Up of Fracture Surface, 1000X

SEM – Close Up of Fracture Surface, 1000X

NTS Baltimore announces the addition of the new JOEL InTouchScopeTM JSM-6010LA Scanning Electron Microscope (SEM) with fully integrated expanded EDS (energy dispersive X-ray analyzer).

SEM - Overview of BGA Solder Joint, 90X

SEM – Overview of BGA Solder Joint, 90X

This research-grade SEM provides high resolution imaging and a range of acceleration voltages in both high and low vacuum modes.  The embedded JEOL EDS system with silicon drift detector technology now includes spectral mapping, multi-point analysis, automatic drift compensation, partial area, line scan, and mapping filter functions.  Additionally, the JSM-6010A features simultaneous multiple live image abilities that allows the client to view images remotely with magnifications from 5X – 300,000X.

SEM - Overview of Surface Pitting, 400X

SEM – Overview of Surface Pitting, 400X

“This new “live” capability will allow NTS to work more closely with our clients, allowing them real time access to their analysis from the comfort of their office”, stated Keith Sellers, Operations Manager at NTS Baltimore, adding, “From there, the client can provide immediate instruction as to how the analysis can be focused or how the analysis can be changed to meet their specific need”.

Learn more about the SEM/EDS Analytical Services on our main website or contact us today to discuss your next program.

Testing to the Extreme: NTS Designs and Builds Custom Pneumatic Test Setups in Support of Customers’ R&D Needs

Temperature Testing over 2000F with airflow.

Temperature Testing over 2000F with airflow.

NTS Santa Clarita is home to our largest pneumatics test capabilities. The pneumatics test facilities are designed to conduct testing of air flow, pressure and temperature management subsystems and components requiring compressed air in a controlled environment. Other environments which can be combined with pneumatic testing include; external thermal control, structural stress, and vibration.

The pneumatics test system is comprised of four high-capacity convection heaters, seven air compressors with boosters, two compressed air receivers (ullage tanks), air distribution piping and controls, high flow, low pressure air blowers, and supporting capabilities such as thermal chambers, small air compressors, LN2 and GN2.

Typical systems and components which NTS tests in our pneumatics testing facility include:

  • Jet engine bleed air systems and associated components (valves, instrumentation, etc.)
  • Aerospace environmental control systems and associated components (heat exchangers, valves, instrumentation, etc.)
  • Transportation and industrial combustion and exhaust management systems and associated components (heat exchangers, valves, turbo chargers, instrumentation, etc.)
  • Other subsystems and components that require compressed air at varying pressures, flows and temperatures for sustained periods.

To learn more about this test capability, click here.

Meet your Testing Team at NTS Detroit

Detroit_Team

(Left to right) Geoff Polan, Dynamometer and Hydraulics Manager Mike Garvey, Regional Sales Manager Loren Isley, Applications Engineer (Quoting) Steve Patykowski, Vibration and Climatics Manager

Our technical team at NTS Detroit has the experience and capabilities to provide world class testing services. We are with you every step of the way from development of requirements, creation of tooling, configuration of test equipment and performance of testing, to documentation of results.

Geoff Polan is a mechanical engineer with 10 years of experience in automotive powertrain and chassis components, subsystems and vehicle level applications. He specializes in dyno testing of drivelines, gearboxes and electric motors. Also skilled with electro-mechanical and test automation, Geoff manages our dynamometer and hydraulics groups and works with customers to plan testing programs.

Mike Garvey’s background consists of 30 years developing and performing test programs. His expertise spans across the entire enterprise, giving him a broad knowledge of all service offerings. Mike is our Regional Sales Manager covering Michigan and portions of Ohio. He communicates closely with the NTS quoting and operation teams in Detroit to ensure that your test requirements are met.

Loren Isley is our Chief Engineer and PE, bringing 45 years of expertise in design, manufacturing and use of test equipment, with a deep knowledge of mechanical and electrical testing. He leads the quoting team and helps to personally develop test plans and requirements, providing efficient costs and timing for your program.

Steve Patykowski is a mechanical engineer who has been performing test and analysis of electro-mechanical issues for over 20 years. He specializes in shock & vibration testing as well as environmental simulation of automotive, aerospace and commercial products. Steve manages our vibration and climatics groups and is also excited to assist in planning your test program.

Geoff, Mike, Loren and Steve would love to speak with you about your test needs! Call the Detroit lab today at (313) 835-0044. 

Testing for UL Recognition – A Step by Step Guide

NTS UL Testing InfographicLeading Companies Choose NTS for UL Testing

NTS Anaheim and a number of other NTS laboratories offer UL Engineering and Administrative Client Agent Services and Testing to help you achieve UL Recognition for your product. NTS Anaheim is the ONLY UL Data Acceptance Program (DAP) certified lab for materials testing in North America.

What does this mean?

It means that NTS can evaluate and test your product and send our reports directly to UL  for recognition. Once UL approves the data, they will send a Notification of Authorization (N of A) to apply the UL certification mark.

Why would you use NTS for UL standards testing?

NTS is a fully certificated laboratory under the UL Third Party Test Data Program (TPTDP). We can get your project started faster, provide pre-program engineering, pre-screen testing, direct engineering contact, custom artwork optimized for PWB/PCB recognition, and sample preparation provided on LTTA test programs.

How does it work?

In the engineering phase, the generic or elevated RTI (via aging) are discussed and recognition parameters are defined.  Complex or unusual constructions are welcome to be submitted for evaluation.

Next, NTS and UL quotations are provided and upon acceptance, final sample requirements are determined. The samples are sent to NTS laboratories, and NTS CNC routes samples from your laminate. Samples are processed immediately to determine acceptance and frequent aging updates with RTI projections are provided.

Depending on the project scope, NTS will prepare and submit reports for short term indexing and provisional and final recognition of products.  Following UL’s acceptance they will issue a Notice of Authorization.

NTS UL Testing Approvals

NTS has unmatched experience evaluating industrial laminates, plastics, HDI materials, printed circuit boards, and soldermask materials. We specialize in the following categories:

UL 796 Printed Wiring Boards
UL 796F Flexible Materials Interconnect Constructions
UL 746A Polymeric Materials – Short Term Property Evaluations
UL 746B Polymeric Materials – Long Term Property Evaluations
UL 746E Polymeric Materials – Industrial Laminates, Filament Wound Tubing, Vulcanized Fiber and Materials used in Printed Wiring Boards
UL 746F Polymeric Materials – Flexible Dielectric Film Materials for use in Printed Wiring Boards and Flexible Materials Interconnect Constructions
UL 94 Flammability
UL Subject 5703 Outline of Investigation for Determination of the Maximum Operating Temperature Rating of Photo-voltaic (PV) Materials
Short Term Aging and Pre-Screen Testing

The UL Certificated Agency Program (CAP) Scope of approval covers the following categories:

ZPMV2 – Wiring, Printed – Component (Rigid PCB’s)
ZPXK2 – Wiring, Printed-Flexible Material Constructions – Component (Flexible and Flex-Rigid PCB’s)
QMTS2 – Polymeric Materials – Filament-wound Tubing, Industrial Laminates, Vulcanized Fibers, and Materials for Use in Fabricating Recognized Printed Wiring Boards – Component
QMJU2 – Coatings for Use on Recognized Printed Wiring Boards – Component (solder masks)
QMFZ2 – Plastics – Component
OCDT2 – Insulating Devices and Materials, Miscellaneous – Component

Contact us today to discuss how NTS can help you achieve your UL approvals faster and more cost effectively.

How can I relate the results of MIL-STD-810 salt fog testing to the life time of my product?

This is a very common question that we get asked quite often and unfortunately there is no correlation between what the product sees in the salt fog chamber to what it will experience out in the field. In order to understandSalt Fog Testing why, you must first understand the purpose of the test.

Originally stated by V.J. Junker in The Evolution of USAF Environmental Testing(1), the test is to determine the resistance of aerospace ground and aerospace equipment to the effects of a salt atmosphere.

According to Mil-STD-810G, the test is performed to determine the effectiveness of protective coatings and finishes on materials. The stated purpose of the test is to determine design flaws such as dissimilar metals, improper coatings, uncoated materials, electrolytic action, binding of parts, etc. Therefore, results can be related to the suitability or quality of parts or assemblies, but cannot be directly related to exposure time in the marine environment.

Salt Fog and Salt Spray testing are conducted at 14 NTS locations across the country. Visit our locations page to find the lab closest to you!

(1) Junkers, V.J. The Evolution of USAF Environmental Testing, Technical Report AFFDL-TR-65-197, October 1965.

Q & A: Do I need a fixture for vibration testing?

Vibration Testing FixtureQuestion: One of the Qualification test requirements for my product includes vibration testing. Do I need to provide a test fixture in order to perform the vibration test?

Answer: The primary purpose of a vibration test fixture is to adapt the service mount of the unit under test (UUT) to the vibration test equipment (shaker, slip plate, etc) and to transmit the intended vibration to the UUT with as much fidelity as possible.

In order to accomplish these goals, a fixture should include good engineering design, specific materials and precision fabrication. Of course, all of these factors combine to make vibration fixturing both relatively expensive and time consuming to produce. This is undoubtedly why many companies seek to forego the design and build of dedicated fixturing and to seek other means of attaching their test items to the vibration equipment or simply leave it up to the test lab.

When no fixturing is provided, the test facility must find a way to attach the test item to the vibration equipment however they can. This usually means strapping or clamping the articles using eye bolts and nylon straps or threaded rod and clamp bars placed across the test item. As you can imagine, there are compromises inherent in this approach.

First, most test specifications are written with the assumption that the vibration will be input at the service mount of the test article. Strapping or clamping items to the vibration equipment rarely allows for this.

The second challenge is that there is a limit to the force that can be applied to an item by strapping or through clamp bars. Therefore, coupling between the test item and vibration system is usually compromised. This typically results in a frequency selective transmission of the vibration with some frequency bands being under the desired amplitude and other frequencies being over the intended amplitudes. The net result can be an under-test or over-test of the test article.

Finally, control of the input vibration levels can be compromised due to the ambiguity of sensor placement for control and monitor accelerometers. These locations are usually provided as an aspect of good fixture design.

So when vibration testing of your product is required, always weigh the time and expense of fixturing against all of the possible compromises inherent in the undefined approaches of clamping/strapping or “best way” mounting as decided by the test facility.

Is there a preferred sequence for EMI, EMC Tests?

EMI Testing NTS BoxboroughOne of the questions we get asked often is about order of EMI/EMC testing.  Neither MIL-STD-461 nor RTCA/DO-160 specify the order of test performance.  Leaving aside the issue of Safety of Flight tests for aircraft (which typically must be performed prior to any other testing), there are a few different approaches to take in this regard.

The first approach is to perform an analysis of the equipment under test (EUT) before going to the lab to determine what tests are most likely to cause problems, and to start with them.

This approach works best if a customer does not have any idea how their product will stand up to the EMI/EMC compliance requirements. A design analysis tends to vet out significant concerns up front, potential design solutions can be discussed prior to qualification testing. At this point, the Subject Matter Expert (SME) should be able to prioritize the threats, and work with the customer to develop a suitable test order. This approach also provides an opportunity for pre-qualification evaluations to ensure the product will not have any issues during the qualification program.

The second approach is to begin with the most benign tests, usually the emissions.  These tests have virtually no chance of harming the EUT, but they sometimes prove to be the most problematic.  Emissions testing tends to reveal inerrant design flaws the most, and generally requires some level of redesign. Changes in design could necessitate repeating other tests if emissions is not completed first. However, there may be cases were a customer feels their product does not have any emissions concerns but is likely to be susceptible to a particular immunity test. They may choose to get the immunity evaluation out of the way first, and allow time for potential modifications prior to commencing with the remaining tests. This approach would also avoid costly retests or delays due to changes to the EUT.

The third approach is to begin with the most potentially damaging tests first. The philosophy here is that all is well and good if the EUT endures those tests with no issues.  However, if there are susceptibilities that require repair/redesign, those problems can be resolved before continuing with the other tests.

In summary, the EMC / EMI testing sequence used should be an iterative decision between the lab and the customer to determine which approach best suits the product and customer’s needs.