Testing


We regularly perform material characterization testing, including industry standard ASTM and SACMA tests for monolithic and sandwich composites (tension, compression, short and long beam shear). We also characterize metals using standard ASTM tests, with one major area being NHRA chrome-moly chassis tube characterization.

We also perform prototype component and product testing. Such testing covers a wide range of subjects, from motorcycle footpegs to spacecraft landing gear.

We perform modal vibration testing, usually in the field, commonly for design verification of completed products for our clients. Verification may consist of minimum natural frequencies, damping quantification, or full modal characterization.

We perform testing to support legal cases, which in some cases is design verification, and in others is failure reconstruction. Sometimes these tests are done in the field. See the legal section for project examples.

Supporting the lab, we have in-house model shop capabilities for composite and metal test sample prep, fixture fabrication, and test article/prototype fab (cutting/sawing, CNC milling, lathe turning, TIG and stick welding, woodworking). We often design and build special fixturing to execute accurate tests of unique subjects.

Convergence Engineering has various methods for test article loading, including multi-location computer controlled hydraulics that can be used closed loop, in either force or position control mode. We use digital data acquisition systems to record data. Our load frame capacity is 25 kip, and can be used for low frequency dynamic loading for fatigue simulation.

We are experienced in the use of photogrammetric deformation measurement, as well as the use of common sensors (strain gages, accels, etc).


Following is a summary of test projects executed at our laboratories and in the field.

Material Characterization | Aerospace | Motorsports | Other Topics

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Material Characterization

 
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Aerospace

  
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Motorsports

   
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Other Topics

  

Tension Testing

CEC has performed many tension coupon sample tests on a wide variety of materials, ranging from plastics to composites to exotic metals. CEC’s 20 kip load frame is usually used. Both load and displacement control testing can be done, via computer control, with direct strain gage or crosshead measurement. We commonly perform chrome-moly tubing cert tests for NHRA teams and chassis builders. We have capability to apply elevated temperatures and fluid conditioning to samples for special applications.

Compression Testing

CEC performs compression testing of fibrous composites regularly, and we have SACMA/ASTM standard guide fixtures for such tests. We normally prepare the samples on site, including epoxy tab bonding, tab squareness machining, and strain gaging.

Beam Testing

We perform standard ASTM short beam shear and long beam shear/bending tests, usually on composites and sometimes on plastics.

Special Coupon Testing

CEC performs special coupon-type testing, such as this graphite composite flange compression testing. In this case, CEC developed a new custom fixturing system that allowed lower cost testing of large sample quantities without tab bonding. Special tensile testing is also performed on flanges and other subjects.

Thread/Fastener Tests

A thread pullout test is a simple test that can characterize the maximum load capability of different grade nuts and bolts of different sizes, when handbook data are not available or sufficient for the problem at hand. For example, a legal case required CEC to characterize the actual failure loads of 5/16 UNC nuts of several materials grades, and lengths.

Special Sandwich Tests

We sometimes perform unconventional tests on sandwich composites with fastener inserts. Here, for example, we performed a bending load test on a Titanium insert mounted within a composite sandwich sample, to quantify the “wrenching” moment load capacity of the as-molded fastening system.

Sandwich Pullout Testing

Here, a graphite skinned honeycomb sandwich square (barely visible within the bottom of the steel fixture), with a bonded in metallic threaded insert, is pullout tested to establish design allowables. This particular setup included simultaneous shear force loading as well via a fixture bar to a chain loader assembly.

JSF Composite Duct

CEC tested a ½ scale composite duct to simulate bending moment of turbine blade failure of the Joint Strike Fighter. The objective was to optimally design and verify the engine bypass duct for buckling resistance under lateral bending moment. Test fixtures were built in house which used three 4 inch hydraulic cylinders up to 3000 psi to load the sample. A computer program was developed to control the loading with closed loop control based on both force and displacement at different phases of the test, so that post-buckling could be well controlled. A series of displacement transducers (string pots and LVDTs) were used to measure displacement of the hydraulic cylinders and buckling of the composite duct structure surface. Three clevis pin load cells were used to measure the force present at each hydraulic cylinder.

The duct was tested with and without side duct openings. With openings, deflections were gradual and reversed as load was increased. Without side ducts, the buckling was very abupt at very high load, producing an unusual deformation pattern virtually instantaneously with high energy noise release. Strain gages were used to measure the stress present at key locations determined by FEA modeling. CEC’s 16 PC based data acquisition system was used to record and monitor force, displacement, and strain outputs in real time, and at the same time control the loading closed loop.

A process called photogrammetry was used during this experiment. Multiple photos were taken at different angles simultaneously with a calibrated camera. The white dots in the photo are used in calculations based on the photos to determine actual surface 3-D shape before and during loading. Thus, using computer software; displacement of each point can be calculated relative to its original location. This process allowed us to characterize the deflection of the entire surface of interest without the use of a large number of sensors, and without using expensive methods such as laser interferometry.

Landing Gear Leg

CEC designed and built a test structure for a prototype spacecraft landing gear leg. The goal of the project was to simulate the force impact of an actual landing. 30,000 lbf of force was applied to the landing gear leg in 0.5 seconds. A hydraulic system was designed for high pressure, high flow rate, and extremely quick response time to properly simulate the impact. Using a specially designed computer and electronics control system, CEC was able to nearly instantly apply full force and stop the motion on command, within a travel of 10 inches in fractions of a second.

The primary mechanical element was a moving carriage, on an I beam track, that included a concrete contact surface for the leg, and was made very lightweight to reduce inertial force loss and slow down the impact. The high flow rate accumulator, valve and hydraulic ram drove the carriage directly, against a strongback.

This is an example of a test project that required a lot of FEA analysis for fixture design. Properly designed test fixtures provide for more accurate measurement of results and better simulation of the desired phenomena. And of course, testing safety is ensured by the accompanying stress analysis and sizing (including weld sizing).

Prototype MX Footpeg

Failure testing was performed on OEM and prototype foot pegs. Deflection and loading measurements were recorded. Head to head comparison between OEM and the prototype peg load capacity and stiffness was made. ST designed and built the necessary fixtures in-house, to utilize OEM peg attachment bracketry.

MX Lever/Perch

CEC aided in the design of a new break-away clutch/brake perch and lever with FEA models. Then CEC performed maximum load verification testing, with load applied at the end of the lever. Using a string pot deflectometer, a load-deflection curve was also developed from the data recorded. This enabled checking the “mushiness” of the new lever design for suitability compared to OEM parts.

Top Fuel Chassis

NHRA Top Fuel dragsters are incredible power-producing machines. the stress levels in the frames can be very high. CEC performed trackside testing to characterize the loading on the chassis during actual ¼ mile runs. Then a laboratory head to head comparison between condition-N and heat treated chrome-moly tube frames was conducted on a specially designed test fixture made by Chuck Hasse’ of New Orleans, and modified by CEC for closed loop force control testing. Wing loading, wheel loading, driver/engine weight, engine torque, engine exhaust thrust, acceleration load transfer, and simulated bounce were all applied via computer controlled hydraulics through the fixtures.

Funny Car Chassis

A similar test to the Top Fuel chassis test was conducted on a funny car frame to support Gotham City Racing’s new funny car development in New Orleans. This test was conducted by CEC at the client’s chassis builder’s location on a similar test fixture assembly tailored for the shorter FC chassis. Aero loading from the body and wheel loading/engine torque were applied. The car was tested with and without certain frame cross members to characterize deflection and stress influences due to those cross members.

NHRA Tube Testing

As a result of CEC/ST’s Top Fuel drag car chassis testing, and problems with frames breaking in the 2005-2006 seasons, SFI/NHRA has mandated certain material minimums allowable for tubing in Nitro cars. CEC performs strength and elongation testing of such tube samples, in our 20kip load frame. We use an ASTM A307 dogbone sample cut from the tube (instead of whole tube), which allows much lower cost testing for the industry. Every Nitro car built now requires this certification testing, and it has successfully solved on-track failures that are life-threatening to the drivers.

Heat Exchanger System

CEC provided lab facilities and built up a heat exchanger test system for a high power laser for affiliate Sierra Engineering. The system used a heat exchanger to transfer heat from an ethylene glycol (EG)/water circuit to a liquid ammonia circuit, with the EG output temperature requiring very tight control. The ammonia phase change to gas was utilized to add to the cooling performance. Moderate speed closed loop control with electromechanical valves was required, and the control algorithm was the main subject of study during these tests. CEC built a specialized PC control and acquisition system for the testing program, measuring pressures, temperatures, and flow rates.

The ammonia gas exhaust was processed via a tall stack water scrubber designed and fabricated by CEC. Aqueous ammonia was the result, which was mixed with phosphoric acid and used as high quality fertilizer in agricultural operations in the locale.