Laboratorio Structural Dynamics
The unique equipment characterizing the CITEEC Structural Dynamics Laboratory is the drop tower for impact tests. It's an infrastructure designed and intended for conducting impact tests on structural components and materials. The infrastructure was funded 80% by FEDER funds and 20% by the Xunta de Galicia thanks to a research project by the Structural Mechanics Group (GME) at UDC. Its construction and installation were carried out between July and October 2020 by the company VTI (Vázquez y Torres Ingeniería S.L). The first tests were conducted in November 2020.
The tower is comprised of a metal platform of 2.5m x 2.5m supporting two pillars of 7m in height and an upper closing beam. A lifting carriage runs between the two towers, holding an impact carriage with a dynamic load cell and an impactor at its end, using a pneumatic system. This allows for its release and fall from various heights. Therefore, the impact carriage is released at the desired height and impacts the structure fixed to the platform. The system is fully automated and ensures maximum safety.
To conduct tests on complete structural components of different materials, as well as specimens of lightweight materials like foam or cork to study their dynamic properties, four impact carriages of various sizes are available. These range from an ultralight one with a mass of 5 kg to a heavy carriage with a maximum load of 500 kg, with the possibility of increasing mass increments between 1 kg and 20 kg in different configurations. These masses, combined with the ability to drop them from 0.5 m to a maximum height of 5.5 m, result in a testing energy range for the tower from 10 J to 25 kJ, with speeds of up to 10.4 m/s, and the possibility of increasing the maximum energy through a vertical elastic system.
The tower is activated by a geared motor that moves an irreversible trapezoidal threaded spindle, raising the lifting carriage. The connection between the lifting carriage and the impact carriage is pneumatic, and displacement, speed, and weight measuring systems are available for test control, along with a safety rebound damping system on the platform. To prevent vibrations in the rest of the CITEEC and isolate the tower, a 50-ton reinforced concrete pad, isolated from the rest of the laboratory, was executed, to which the tower is anchored with four pre-stressed bolts.
The measurements from the dynamic load cell and accelerometers are collected by a dual data acquisition system: Beckhoff cards with a sampling range between 20 kHz and 50 kHz for tests with metallic structures or more flexible systems; and a Tasler card with 4 high-speed channels capable of sampling up to 2 MHz for impacts with fragile materials such as reinforced concrete. Additionally, there are high-speed cameras for recording the test (since the test pieces deform in milliseconds) and analysis using digital image correlation - DIC.
The testing area has a width of 1 m and a bench length of 2.5 m, expandable up to 6 m in the case of testing metallic or concrete beams with supports located outside the bench.
The tower allows impact testing of automotive, aeronautical, or railway structures and components; for example, tubes for absorbing energy in the frontal impact of automobiles, or those used in aircraft fuselages and landing gears to reduce the consequences of a forced landing. It's also possible to test components such as bumpers, airbags, road bridge barriers, parapets, and traffic containment systems, as well as generally any system that must withstand impacts within the covered energy and velocity ranges.
This infrastructure complements the energy absorption system design capacity of the Structures Mechanics Group, based on simulation and numerical optimization. With this new equipment, experimental verification and validation of designs can also be carried out.
This infrastructure offers all companies and research groups in the CITEEC environment the opportunity to test their prototypes against impact loads.