Shock Fixture Design Best Practice for Reliable Test Results
Why Fixture Design Is Critical in Shock Testing
When it comes to high-precision shock testing, a well-designed fixture isn’t just a mechanical support—it's the bridge that connects your test equipment to accurate, repeatable results.
There's a common myth that experienced engineers can design shock fixtures based purely on intuition. While experience is invaluable, reliable fixture design depends just as much on structured analysis, mechanical principles, and accurate calculation. Whether you're validating automotive components, electronics, or structural assemblies, skipping detailed fixture planning can lead to test failures, inconsistent data, or even equipment damage.
At TMC Solutions, we emphasize a data-driven approach to fixture design, ensuring every shock test is built on a solid mechanical foundation.
The Role of Fixtures in Shock Testing
Fixtures serve as the mechanical interface between the shock testing machine and the device under test (DUT). Their role is twofold:
Securely mount the test specimen without introducing unintended stress or distortion.
Efficiently transfer shock energy from the shaker or drop table to the DUT.
A poorly designed fixture can absorb or distort part of the shock, skewing results and leading to misleading conclusions. A well-designed one ensures the DUT experiences the intended stress waveform with high fidelity.
Targeting Accuracy: Keep Errors Within 10–20%
Even the best shock fixtures may introduce minor vibration transmission errors. However, keeping these within a 10–20% margin is considered acceptable in most applications. That said, investing time in reducing fixture-related inaccuracies is a hallmark of excellent test engineering.
By minimizing such errors, you reduce variability in test results, improve correlation with field conditions, and increase the repeatability of your test setup.
Common Fixture Types in Shock Testing
Shock fixtures come in various forms, each suited for specific DUT sizes, geometries, and directional stress requirements. Below are the most commonly used:
1. Flat Plate Fixtures
Purpose: Basic mounting interface between the DUT and the shock machine table. Without such a plate, it is rarely possible to connect the specimen directly to the shock machine table for shock testing.
Use Cases:
Ideal when a DUT cannot be mounted directly onto the shock table.
Protects the table’s bushing and alignment system.
Frequently used as consumables for high-throughput testing.
Tip: For large-volume or long-duration test programs, invest in custom-machined flat plates to reduce wear and improve cost-efficiency over time.
2. Cube-Type Fixtures
Purpose: Enables multi-directional shock testing of small components.
Features:
Mounts directly on the shock table or via a transition plate.
Provides up to six orientations for forward, reverse, and lateral shocks.
Internal screw bushings allow flexible mounting configurations.
Tip: Rotate the fixture to simulate real-world impact directions without re-fixturing the DUT. When the specimen mounted on the top surface is subjected to vertical dynamic shock, the other four planes (on the four sides) can receive parallel shock. Any of the four sides can be rotated 90 degrees (rotated within the base plane) to withstand shock in two directions parallel to the base plane or impact in four directions (impact can be divided into forward shock and reverse shock, so there are two more directions than shock).
3. L-Shaped Fixtures
Purpose: Support asymmetric DUT geometries or when side-mounting is required.
Construction:
Can be assembled using screws, welds, adhesives, or machined as a monolithic part.
Typically used for parts needing perpendicular alignment to the shock vector.
Tip: Ensure high rigidity at the joint to avoid vibration damping.
4. T-Shaped Fixtures
Purpose: Dual-sided mounting for symmetrical DUTs. The T-shaped fixture is similar to the L-shaped clamp except that the vertical plate is mounted in the center.
Features:
Vertical plate is mounted at the center.
DUTs can be attached to both sides simultaneously.
Design naturally balances the center of gravity for smooth energy transfer.
Tip: Use when testing paired components or validating symmetry in response under shock.
Best Practices for Shock Fixture Design
To maximize test reliability and ensure fixture performance, follow these proven guidelines:
✔ Perform a modal analysis of your fixture before finalizing the design. Avoid natural frequencies that overlap with test frequencies.
✔ Use materials with consistent stiffness and damping properties to reduce variation.
✔ Keep the mass of the fixture low relative to the DUT, unless needed for balance.
✔ Secure all connections with appropriate torque to prevent slippage during high-G testing.
✔ Design for repeatability—the same fixture should give the same results every time.
✔ Document fixture parameters and use them in future test planning and simulation correlation.
Precision Starts with the Fixture
The fixture may seem like a passive component in your shock testing setup—but in reality, it’s a critical link in the accuracy chain. At TMC Solutions, we believe that fixture design is an engineering discipline in its own right, deserving the same level of attention as the test method itself.
By combining thoughtful mechanical design, analytical modeling, and hands-on experience, engineers can create fixtures that deliver reliable, repeatable, and industry-compliant results—test after test.
Need Help Designing a Custom Fixture?
TMC Solutions offers tailored fixture design services to match your product and testing needs. Our engineers collaborate closely with clients to develop optimized fixtures for shock, vibration, and environmental testing setups.
📩 Contact us today to discuss your project and receive expert advice.