Accredited materials testing laboratory

Fraunhofer IFAM has a materials testing laboratory certified according to DIN EN ISO 9001:2015. This laboratory is accredited according to DIN EN ISO/IEC 17025:2018 for the procedures specified in the DAkkS certificate. Experiments are carried out to test materials, structures and, in particular, adhesively bonded joints according to standardized and self-developed procedures for example for the automotive industry or rail vehicle construction. The results of these tests form the basis for simulating component behavior. Many of the tests focus on the tensile behavior of fiber-reinforced plastics, but also on the impact strength and peel strength of adhesively bonded joints. Particularly in order to describe the complex behavior of adhesively bonded joints, the researchers also develop customized test methods as required.

The materials testing laboratory is equipped with various test rigs for mechanical testing of materials and components. Especially for polymeric materials, fiber-reinforced composites, adhesives and adhesively bonded joints, structural properties are determined, such as:

• Stiffness and strength
• Fatigue and durability
• Creep behavior
• Fracture mechanical properties

The material characteristic values are provided for finite element simulations, which will also be performed in-house at the customer's request. In addition, the characteristic values can form the basis for the verification of adhesively bonded structures and components, e.g. in accordance with DIN 6701.

Electromechanical and servohydraulic testing machines

The materials testing laboratory offers capabilities to test materials, adhesive bonds and structures up to 2 meters.

The electromechanical testing machines are used, for example, to perform tensile and compression tests on adhesives and adhesively bonded joints and fiber composites. These testing machines are suitable for pull-off speeds of up to approx. 0.01 m/s. Servo-hydraulic and electrodynamic test rigs are available for tests under oscillating loads of up to 50 Hz. Tests with crash-relevant speeds of up to 20 m/s can be carried out on a special high-speed testing machine.

For tests at practice-relevant ambient conditions, almost all testing machines are equipped with climatic or temperature chambers. Currently, tests can be carried out in the temperature range from -50° C to 200° C. In addition, tests in liquid nitrogen (-196° C) are possible. A test system for the range between -170° C and -50 °C is also available.

Static test systems using weights and springs are available for creep tests. In addition, researchers can set up test systems for special applications and component testing.

Tactile and optical measurement systems are available for precise deformation measurements, such as those required for thin adhesive layers.

• Inductive and capacitive sensors
• Video extensometers
• Laser extensometers
• Digital image correlation
• Strain gauges

Choice of test methods

Standardized and non-standardized tests relevant to polymer materials, adhesives and adhesively bonded joints and fiber composites are carried out in our laboratory. The tests results can also be used to identify parameters of material models for the simulation using the finite element method, e.g. material cards for the automotive crash simulation of adhesive joints using cohesive zone models.

With these and other special types of tests - some of which are used in combination - the scientists describe the complex behavior of adhesively bonded joints and composite materials. They are investigating the influence of the hydrostatic stress component and of temperature and humidity on the material properties.

Quality assurance

Among the numerous test methods offered by the materials testing laboratory, six methods are currently accredited by DAkkS.

The accreditation certificate can be found here.

Measurement uncertainties of the tests are considered according to common standards.

Finite element simulation and verification

The knowledge gained from the above tests is transferred to simulation approaches and thus forms the basis for structural analysis and design of adhesively bonded joints for automotive, aerospace, shipbuilding and rail vehicle construction.

Fraunhofer IFAM supports you in establishing material models, material cards and methods for simulating the mechanical behavior of adhesively bonded structures. Different approaches can be taken:

• Continuum mechanical models provide the basis for the detailed local analysis of the adhesively bonded joint,
• simplified substitute models (e.g. cohesive zone models) facilitate prompt implementation in industrial applications.

Example: High-speed tests and simulations before the crash test

Crash tests on complete car bodies are the final development step of new automotives to ensure meeting the occupant safety requirements.

Real tests involve a very high effort in testing technology and therefore very high costs. This costly process is therefore supported by crash simulations. The prerequisite for these simulations are material models that are measured with a high-speed testing machine and verified via finite element models.

Dr. Christof Nagel conducts research in the "Polymeric Materials and Mechanical Engineering" department and heads the materials testing laboratory. He not only provides comprehensive advice on testing adhesively bonded joints, but also on modeling for simulating adhesively bonded structures. The fields of application range from aerospace, vehicle construction and shipbuilding to applications in energy technology.