142/195 Mechanical Shock and Modal Test Techniques

Applications  The effects of shock are important in many engineering applications ranging from appliances to computers to ships to automobiles, trucks and military vehicles to high-performance aircraft and missiles. Shock is often part of the service and/or transportation environment. Military Standards such as MIL-STD-810 call for shock testing.

The possible effect of shock must be considered for almost every product that has to be shipped and handled. Care can be taken in a controlled environment but during the transportation phase the product within its package must be designed and tested to withstand the anticipated environment.

For Whom Intended  Engineers involved with dynamics and structural test applications.

Most engineers need specialized education in order to properly measure, quantize and analyze this generally unfamiliar environment, and to reproduce it in environmental test laboratories. This course is for packaging designers, test laboratory managers, engineers and aides. It also helps quality and reliability specialists and acquisition personnel in government and military activities, and their contractors.

Instrumentation specialists who will measure transportation, service and laboratory shock need this course. Metrologists learn about shock calibration of accelerometers and systems. Project personnel, structure and packaging engineers learn about developmental shock testing. Product assurance and acquisition specialists learn to evaluate shock test facilities and methods, and to interpret shock test specifications.

This course is designed to serve the varied needs of scientists, engineers, aides and senior technicians. The instructor maintains good balance between practical training and theory.

Brief Course Description  The course begins with a review of structural and dynamic theory before examining methods of measuring frequency response from the structure under test. The causes and effects of shock are reviewed in detail, including the different shock pulse shapes.

Experimental modal testing is introduced by a brief discussion of theoretical modal analysis. The single degree of freedom (SDoF) model enables us to understand the fundamental concepts of free and forced vibration, natural frequency, resonance and damping. However in MDoF systems, resonance may occur at a number of different frequencies, each of which corresponds to a different pattern or shape of the system's motion. These are known as the natural or normal modes of vibration or mode shapes. There is a differential equation of motion for each degree of freedom; a set of n simultaneous equations is needed to mathematically describe a MDoF system. These equations are usually solved using matrix algebra.

In the experimental method of Modal Testing, the structure is excited by applying forced vibration and measuring the responses, from which the vibration modes are determined and a structural model developed. This is the reverse process to the theoretical method. Various methods of input excitation are discussed, such as shaker and impact hammer. Structural preparation and suspension methods are also examined.

A review of transducers and signal processing equipment is made before discussing analysis methods, time-domain curve fitting. Modal test philosophy including the sequence of steps and practical considerations in undertaking the test are discussed. The tabulation of results and derivation of mode shapes and construction of spatial models (mass, stiffness and damping) are covered before discussing the application of the modal test results.

The Shock Response Spectrum (SRS) is discussed as it relates to shock measurement and testing. The course then covers shock measurements, also calibration. The relative merits of various types of shakers and shock test machines are briefly considered before covering various shock test methods, including pyrotechnic shock testing. Some typical shock test procedures and specifications are described, both military and commercial.

Diploma Programs  This course is required for TTi’s Dynamic Test Specialist (DTS) and Mechanical Design Specialist (MDS) Diploma Programs. It may be used as an optional course for any other TTi Specialist Diploma program.

Related Courses See TTi’s Course 142, Mechanical Shock Techniques, and Course 195, Modal Analysis for Structural Validation, which were combined to create this course.

Prerequisites  Prior participation in TTi’s Fundamentals of Vibration would be helpful. Participants will need first-year college mathematics (or equivalent experience) and some facility with fundamental engineering computations. Some familiarity with electrical and mechanical measurements and vibration will be helpful.

Text  Each student will receive 180 days access to the on-line electronic course workbook. Renewals and printed textbooks are available for an additional fee.

Course Hours, Certificate and CEUs  Class hours/days for on-site courses can vary from 14-35 hours over 2-5 days as requested by our clients. Upon successful course completion, each participant receives a certificate of completion and one Continuing Education Unit (CEU) for every ten class hours.

OnDemand  OnDemand Internet Complete Course 142-4 features over 18 hours of video as well as more in-depth reading material. All chapters of course 142-4 are also available as OnDemand Internet Short Topics. See the course outline below for details.

Course Outline

Summary

Final Review

Award of certificates for successful completion

Click for a printable course outline (pdf).

Revised 6/18/2018