Apparative internship

The apparative practical course "Construction Methods & Materials" is jointly supervised by three institutes LRT 4, LRT 5 and LRT 6. Three experiments take place at the Institute of Lightweight Structures:

• CFRP tensile test
• Nonlinear effects and stability
• Experimental modal analysis

General data about the module 

Qualification goals

1. The students know the essential mechanical testing methods and can meaningfully classify their areas of application.
2. Students will be able to define, set up and carry out material and structural tests independently.
3. The students understand the application and operation of the essential measuring methods and measuring devices used in mechanical testing.
4. The students learn about possible sources of error during test execution and evaluation and can estimate the influence of the errors.
5. Students are sensitized to results from theoretical and experimental investigations and know how to deal with or interpret any discrepancies between theory and experiment.

Content

CFRP tensile test:

• In this test, characteristic values of laminates made of carbon fiber plastics with different fiber orientations are first estimated theoretically using the Classical Laminate Theory (CLT). The test forces to be expected in the subsequent tensile test can also be estimated here.
• Specimens with different fiber orientations are then tested in uniaxial tensile tests to determine characteristic values such as the modulus of elasticity and stress-strain curves. A modern optical strain measurement method, digital image correlation (DIC), is used for this purpose.
• The experimentally determined characteristic values can finally be compared with the values calculated in the CLT. In an iterative process, input variables of the calculation can finally be adjusted to bring calculation and experiment into agreement.

Nonlinear effects and stability:

• High-performance lightweight structures, such as those used in aerospace engineering or aircraft construction, are primarily built from thin-walled structures. Stiffness-dominated criteria (e.g., avoidance of buckling or buckling) play a major role in the design of such structures. Due to the high stresses, the influence of pre-deformations and imperfections is also relevant. In this experiment, these aspects will be investigated in two parts:
  • Investigation of nonlinear effects using the example of a pre-curved flexural beam.
  • Investigation of the stability failure of a U-profile. Different profile lengths as well as the influence of ribs will be considered.

Experimental modal analysis:

• In the Structural Dynamics Practicum, students learn the fundamentals of dynamic structural testing. In the course, the dynamic behavior of the vertical stabilizer of a Eurofighter under periodic and transient excitation is determined: The focus of this investigation is the introduction of experimental modal analysis, methods of signal conditioning and the proper use of relevant vibration measurement techniques.
• The practical part is divided into the following sections: 1. supervised implementation of procedures for the determination of modal parameters as well as methods of signal conditioning, which will be used for the analysis of vibration data during the practical experiment. 2. independent implementation of the experimental modal analysis on the test stand.