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Cockpit eines Autos von Innen im Stadtverkehr

Practical examples Industry: Mobility

Cockpit eines Autos von Innen im Stadtverkehr© lzf
Plastic components are indispensable in the field of modern mobility. Detailed analyses allow material defects to be rectified in the event of damage, thus contributing to the safety and longevity of means of transport and vehicles.
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Examination of operational stability

of retaining claws for conductor rails

Figure 1: Test arrangement in the fatigue test on holding claws IKV

Problem: Component testing to investigate the fatigue strength of retaining claws

For the operation of the Wuppertal suspension railroad, so-called retaining claws made of 30% glass fiber reinforced polyamide 6 (PA6 GF30) are used, which structurally fasten the conductor rail along the entire route. The retaining claws are arranged in pairs to grip the conductor rail. During installation and operation of the track, the retaining claws are subjected to both static loads due to the rail’s own weight and oscillating loads when passenger trains pass over them. To ensure the operational safety of different samples of a new batch, the retaining claws are characterised with regard to their mechanical properties under static and dynamic cyclic loads. Batch inspections are indicated due to regular replacement intervals.

Analysis method: Quasi-static testing and fatigue tests based on field tests

Laboratory tests are used to experimentally determine the force/elongation behavior and the subsequent correlation with static loads in the installed state (field test) as well as the static loads in connection with assembly processes, such as hanging, bending in a curved position or hammer blows.

Further field tests are used to determine dynamic loads that occur when passenger trains pass. The mean and peak loads determined from both field tests are used as input parameters for dynamic-cyclic fatigue tests in the installed state and serve to check the operational stability.

Result: Confirmation of operational stability under laboratory conditions

Result of the field tests, from which the strains on the retaining claw are derived based on assembly processes (1-3 hanging of the rail, 4 bending of a curve and 5 hammer blows). IKV

Based on the strain loads determined in field tests using assembly and overrun processes, average loads and peak loads for the dynamic fatigue test can be assigned in correlation with the laboratory tests. Based on this, retaining claws are dynamically and cyclically loaded at an average of 2,500 N +/- 700 N for up to 5 million load cycles. All pairs of retaining claws tested achieve the target number of load cycles of 5 million load cycles without any abrupt changes in their properties, resulting in an estimated fatigue strength of approx. 12 years. As replacement intervals are scheduled in the maintenance plan after ten years, the retaining claws can be used as intended.

Determination of the

Damping behavior of bearing materials

Ship [Polarstern: Alfred Wegener Institute Helmholtz Center for Polar and Marine Research] and hull with drive shaft IKV

Problem: Determining the damping behavior of bearing materials

Water-lubricated bearing solutions based on thermoplastic polyurethane TPU, a largely new material for this application, are used in the drive train of ship shafts, which can be classified in terms of size between motor yachts, cruise ships and icebreakers. These materials are typically manufactured by casting or injection molding. The damping properties of the TPU material are determined in order to be able to classify how the ship’s shaft behaves in heavy seas. For better classification, materials with known properties for the application are included (e.g. PTFE, PA 6.6).

Methodology: cyclic pressure tests on the hydropulser

  • Dynamic cyclic vibration test using a hydropulser IKV

    Removal of cylindrical test specimens from bearings

  • Dynamic-mechanical analysis to classify the temperature application range of the TPU material

  • Determination of the damping properties at different compression levels under dynamic cyclic compression-threshold loading

  • Illustration of real cases: normal sea state with 1 % compression, heavy sea state with 2 % compression.
  • Comparison of the damping capacity of the materials

Result: Broad spectrum of damping properties recorded

Strain measurement in long-term testing IKV

In the final result, all TPU materials investigated show damping values between 0.02 < tan d < 0.16 in the value spectrum for PTFE and PA 6.6. The highest possible damping is considered to be advantageous, as it sensibly absorbs (“cushions”) the incident energy in the form of impacts on the shaft and converts it into heat. In future, materials can be selected based on the properties determined and tailored to the respective function.

Crack propagation

on a CFRP engine hood

Car with hood made of CFRP (carbon fiber reinforced plastic) IKV

Problem: Describing the failure behavior of CFRP

Carbon fiber reinforced plastics (CFRP) are already widely used in the automotive industry due to their potential in lightweight construction. When designed accordingly, the components exhibit excellent rigidity. In the individual layers of these often highly stressed components, unfavorable orientation and concentration of the forces to be transmitted lead to failure of the composite. The failure behavior must be analyzed in test procedures that take into account the special requirements of the application, material and processing.

Methodology: Check tear propagation behavior

According to the problem described, the separation behavior of CFRP components within the layers is to be analyzed. Among other things, the tear propagation behavior is determined in accordance with the ASTM 5528 standard. The test specimen is created as a composite using the defined manufacturing process and, if necessary, conditioned in a defined climate. In addition, a defined pre-damage is created within the layer to be tested. To adapt the test specimen to the universal testing machine used, a device is used that applies the typical tear propagation load to the composite. The laminar failure behavior of the composite is determined as a function of the applied load, the duration of the load application and the selected loading speed.

Universal testing machine with device that applies the typical tear propagation load to the composite IKV

Result: Comparable characteristic values

Based on these investigations, the aim is to achieve efficient utilisation of the components across the entire component. Through detailed knowledge of the behaviour of the overall component in the event of pre-damage, the economic benefit can be specifically increased with precise optimisations.

Investigation

of plastic fuel tanks

Problem: Reduction of the barrier layer thickness in the pinch weld area

Plastic fuel tanks usually consist of a PE/EVOH/adhesion promoter multilayer system. The tanks are manufactured using the extrusion blow molding process or the half-shell process. Due to the process, there is a significant reduction in the barrier layer thickness (EVOH) in the pinch seam area, which means that these areas have a significantly reduced barrier effect, which can jeopardise approval. Microscopic examinations of the EVOH layer in the critical component area will be used to test the effect of varying process parameters in order to identify an optimum operating point in this respect.

Thin section pick-up of plastic fuel tank in the pinch weld area IKV

Methodology: Microtome sections with selective phase contrasting

First, a thin section was made perpendicular to the course of the pinchweld at room temperature. Since the individual layers of the tank wall hardly form any contrasts in the thin section, selective phase contrasting of the EVOH layer was carried out in a dye solution.

The hygroscopic property of EVOH causes dye absorption (pink-colored in the image). This makes it possible to clearly recognise and quantitatively evaluate the EVOH barrier down to very narrow layer areas

Result: Weak point in the area of the pinch weld

In the bright field, it was thus possible to quickly deliver results with the help of software-supported layer thickness determination accompanied by a wide variation of parameters. As a result, the effect of process parameters on the thickness and quality of the EVOH layer can be visualised and the process can be optimised with regard to product quality.