Modal

The Leader in Modal Testing Services

ATA is the world-leading independent services company for performing modal testing and surveys to characterize structural dynamics.

We have been providing this service for over 40 years, having pioneered numerous technical capabilities including random excitation, multishaker testing, polyreference data processing, and automated test setup processes. Our advancements in our patented Multi-Sine sweep excitation (U.S. Pat. No. 8,281,659), Alias-Free Polyreference (AFPoly) parameter estimation technique, and base shake modal application have all spearheaded improvements in the modal test field. Our ability to deploy well over 1000 channels of instrumentation and data acquisition equipment allows us to complete modal surveys of almost any size structure. We specialize in aerospace structures (aircraft, space launch vehicles, rocket motors, and satellites) but can test virtually any dynamic system.

 

 

End-To-End Modal Test Solutions

The full modal test process involves planning, test performance, and posttest model updating activities. ATA is well versed in accomplishing all phases of the modal test process. Planning activity involves properly selecting measurement and excitation locations along with identifying what modes are of primary interest for the test article. This is a process that is integrated with the finite element modeling activity and requires a tight integration between analysis and test efforts for the highest likelihood of success. ATA is an expert at conducting this process and developing all necessary planning documents that lead to test success. Use of the finite element model (FEM) in developing a test–analysis model (TAM) ensures tight integration between modeling and test activity throughout.

Familiarity with the preparation processes ensures that the test activity follows the proper steps in conducting the test and acquiring all of the appropriate high-quality modal test data. ATA has implemented numerous tools to assess data quality to make sure that all of the results will fulfill the test objectives. Excitation methods are not limited to a single type, as the best results are achieved through implementation of a variety of techniques. Parameter extraction while the testing is ongoing ensures that all test objectives and modal results are obtained before the test is finished. When needed, additional data collection with variations in excitation locations or using different excitation techniques can be applied along with making modifications or additional measurements. Checking all of the results before –removing the instrumentation ensures that there are no missing pieces of information that could necessitate costly test repetition.

ATA’s skill in preparing for and conducting the test contributes to our expertise in the posttest evaluation and model correlation process, as familiarity with the hardware generally leads to a better understanding of where model improvements can be made. Our test engineers are experts not only at completing the testing program but also at conducting or assisting in the FEM updating process. This knowledge and cross-disciplinary skill ensures that the results from the test are well suited for making model improvements and our test engineers have a better understanding when working with analysis engineers in the process.

Modal Test Equipment

ATA owns a large inventory of test equipment which has been tailored to preparation for and performance of large-scale modal tests. Our equipment includes a wide variety of accelerometers, shakers, impact hammers, and data acquisition equipment, all of which are optimized for completing modal tests efficiently. This allows us to conduct small and large modal tests as well as perform multiple tests simultaneously. Our equipment is transportable, which allows testing activity to take place conveniently at our customer’s site. Testing can also be performed at ATA’s facility; we have a 2200 square foot test facility with two T-slot tables for fixturing test articles, along with various handling hardware to accommodate a variety of modest-sized test articles.

ATA also offers equipment rental and expert consulting to facilitate our customers’ conducting their own testing activity.

Test Oversight

Oversight during testing performance is sometimes needed when personnel are just learning to conduct modal testing or learning how to use new test equipment. ATA can provide personnel, with supplemental test equipment, to provide oversight of test performance and help with the entire modal test process. We can review test plans and assist with other customer requirements. Being on site during testing enables immediate data review and recommendations for test adjustments, such as when shaker placement moves or instrumentation changes may be warranted. ATA’s expert advice can help make sure that modal testing is successfully completed.

Base Shake Modal

A fixed base modal test is often desired but difficult to achieve. This is not uncommon in the aerospace satellite industry, when testing and schedule constraints make it desirable to try to obtain modal data with a test article installed on a qualification shake table. Unfortunately, most of the time the flexibility and dynamics of the shaker and shake table do not provide the type of fixed base boundary condition desired, yielding unsatisfactory modal data for the satellite test article. ATA has developed and implemented base shake modal test techniques that enable a fixed base representation of the test article to be achieved, even though the testing is conducted on the less-than-ideal boundary condition of the shaker. With this method, additional base measurements are obtained and used in combination with a standard modal test approach to allow the test data to be constrained to yield the fixed base condition. This approach allows a substantial reduction in the overall development process time while still achieving the desired test conditions for model correlation activity.

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