What Is Resonance Search?
Resonance search is a preliminary test in which the sample's natural frequencies and amplification factors are identified with a low-amplitude sine sweep. It is applied before and after the main vibration tests.
Purpose of Resonance Search
The purpose is to identify critical frequencies and detect structural change through before/after comparison.
Which Products Is Resonance Search Applied To?
- Electronic units
- Automotive and aerospace components
- Battery modules
- Rail equipment
In Which Sectors Is Resonance Search Used?
Standards Related to Resonance Search
- IEC 60068-2-6sine vibration test test
- MIL-STD-810 Method 514
- IEC 61373vibration and shock in railway vehicle equipment test
- IEC 60068series of environmental testing methods test
- MIL-STD-810environmental engineering assessments and laboratory tests test
- RTCA DO-160Environmental conditions and test methods in aviation equipment test
- SAEautomotive and aerospace engineering standards test
- ISO 16750Environmental conditions in vehicle electrical/electronic equipment test
- UN 38.3Transport safety tests on lithium batteries test
Resonance Search Conditions
- Genlik
- Low level that will not cause damage (defined in specification)
- Frequency range
- Band covered by main experiment
- Sweeping speed
- Slow enough to capture resonances
- Measurement
- Transfer function between control and response accelerometers
Equipment for Resonance Search
- Electrodynamic shaker
- Multi-channel accelerometer arrangement
- Vibration control and analysis system
- Mounting fixture
Sample Requirements for Resonance Search
- Response accelerometers must be placed at critical points
- Fixture resonance must be identified separately
- Measurement points must be documented
Duration of Resonance Search
Typically several hours per axis.
Resonance Search Procedure
- 1The specimen is mounted on the fixture and accelerometers are placed.
- 2A low-level sweep is applied.
- 3Resonances are identified from the transfer function.
- 4The same sweep is repeated after the main test.
- 5Frequency shift is compared.
Resonance Search Acceptance Criteria
The acceptance criterion is defined in the specification; typically that the resonance shift between the pre- and post-test searches does not exceed a defined percentage.
Evaluation of Results
A drop in resonant frequency indicates loss of stiffness, i.e. cracking or loosening. The amplification factor points to critical regions.
Resonance Search Report
- Standard applied
- Amplitude, frequency range and sweep rate
- Measurement points
- Identified resonances and amplification factors
- Pre-/post-test comparison
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- Automotive, aviation and rail specifications
Vibration and Shock — What Does This Testing Field Cover?
The section below describes the field that the Resonance Search test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Vibration and shock testing shows whether a product withstands mechanical dynamic loads. The two phenomena are distinct: vibration is a continuous and repeated loading, while shock is a single instantaneous impact at high acceleration. They produce different failure modes and are required separately.
The failure produced by vibration is FATIGUE: a solder joint cracks, a cable sheath abrades, a screw loosens, a connector loses contact. The failure produced by shock is FRACTURE: a brittle component shatters, a bracket breaks, a board comes out of its holder. Testing a product under vibration therefore does not show that it also withstands shock.
Vibration is applied in three forms, each giving different information. Sine vibration sweeps at a single frequency; it is used to find the resonant frequencies of the product and is very valuable at the design stage. Random vibration represents the broadband nature of the real environment and is preferred as evidence of durability. Sine-on-random and random-on-random profiles simulate together the broadband noise superimposed on dominant frequencies from engines and rotors — this is necessary in helicopter and turboprop applications.
RESONANCE is the concept at the centre of the field. Every structure has its own natural frequencies; as the excitation frequency approaches one of them the amplitude grows and the product is exposed to an acceleration many times the input level. A resonance search is therefore carried out before the test, and a design change often takes the form of shifting the resonance rather than lowering the level.
In this family the FIXTURE is part of the result, and this is the most frequently overlooked point. How the specimen is attached to the shaker directly changes the energy transmitted and the resonance behaviour. A poorly designed fixture brings its own resonances into play and imposes a load the product would not otherwise see, or conversely damps the real load and protects the product. Results obtained with different fixtures cannot be compared.
The choice of measurement point also determines the result. The control accelerometer is placed on the fixture and monitoring accelerometers at critical points of the product; the report must document these positions. Accelerations measured at different points in the same test can differ markedly.
Profiles are divided by application area: transport vibration (packaging and shipping), vehicle vibration (by mounting location), rail (EN 61373 categories), aviation (DO-160 sections), military (MIL-STD-810 methods) and battery transport (UN 38.3 T3). The same product passes through different profiles under different programmes.
Method groups in this field
Sine vibration
Determining resonances by frequency sweep and withstand at defined frequencies; the most informative test at the design stage.
Random vibration
Durability with a broadband power spectral density profile; the approach that best represents the real environment.
Combined profiles
Sine-on-random and random-on-random; for dominant frequencies arising from rotating machinery.
Classical shock
Defined acceleration and duration with half-sine, sawtooth and trapezoidal pulse shapes.
Free fall and toppling
Realistic drop scenarios arising from handling; decisive for portable products.
Resonance search and monitoring
Detection of structural change (cracking, loosening) by sweeps before and after the test.
Commonly confused in this field
- Shock and vibration are not the same test; one produces fracture and the other fatigue, and they are required separately.
- A report that does not document the fixture cannot be compared; a fixture can bring its own resonance into play.
- Levels come from the product standard or the programme specification; the standard does not define a single universal level.
- Without a resonance sweep before and after the test, structural damage can go unnoticed; the product may appear to work while being cracked internally.
- The position of the measurement point must be reported; accelerations measured at different points in the same test differ markedly.
- If the product is not operated during the test, intermittent loss of contact remains invisible.
Which decisions these results support
- Verification of transport and in-use durability
- Transport and vehicle vibration conformity for batteries
- Rail, aviation and defence qualification files
- Root cause analysis of solder, connector and joint failures
- The decision to shift a resonance through a design change
Related Tests
Frequently Asked Questions About Resonance Search
According to which standard is Resonance Search made?
Resonance Search is executed in scope IEC 60068-2-6, MIL-STD-810 Method 514 and IEC 61373. The limit values and acceptance criteria to be applied are defined in the product standard; The version valid for your product is confirmed in writing at the offer stage.
Which products does Resonance Search apply to?
Mainly applied to Electronic units, Automotive and aerospace components, Battery modules and Rail equipment. Whether your product is included in the scope is determined by examining its technical specifications and intended use.
Under what conditions is Resonance Search done?
The determining parameters are: Genlik — Low level that will not cause damage (defined in specification), Frequency range — Band covered by main experiment and Sweeping speed — Slow enough to capture resonances. The full terms are in the "Test Conditions" section on the page and vary depending on the product standard.
What kind of sample is needed for Resonance Search?
Response accelerometers must be placed at critical points, Fixture resonance must be identified separately and Measurement points must be documented. The number of samples is determined according to the product standard and the scope to be reported.
How long does Resonance Search take?
Typically several hours per axis. This duration belongs to the experiment itself; sample preparation, queuing and reporting are also evaluated. A realistic schedule for your product is given in the offer.
What is the Resonance Search result called "appropriate"?
The acceptance criterion is defined in the specification; typically that the resonance shift between the pre- and post-test searches does not exceed a defined percentage.