Practical examples Industries: Building & Construction
© GorlovkvHole formations
in polycarbonate multi-skin sheets
Problem definition
Hail damage in the form of perforations in strip lighting on flat roofs of industrial buildings leads to very high costs for building insurers every year. Claims are often settled in the face of the supposed contradiction that, according to literature and existing publications, the damage, which initially appears to be hailstorm damage, cannot be explained by the expected low kinetic energies of small hailstones.
Methodology/Analytics:
Extensive investigations and adjustment tests were carried out at the IKV in order to clarify the cause of the damage to the existing hole formation in PC multi-skin sheets of several hall roofs. This included the construction of a hail impact test rig and the detailed microscopic examination of authentic and reconstructed pitting and associated multi-skin sheet segments with different ageing conditions
Result:
- Extensive cracking on the outside (service life >20 years)
- Elastomer particles exposed on the surface
- Wall thickness loss of approx. 20%
Shot tests were able to reproduce authentic hole formations:
- Projectile diameter 9 mm (PA12 balls)
- Projectile speed 12 m/s
- Kinetic projectile energy 0.04 J
On the basis of the results generated, the contradiction mentioned at the beginning could be dispelled for the cases investigated because it was proven that the damage could have been caused by hailstorms given the obvious ageing of the material. The results of the investigation also make it clear that aspects of the age-related condition of the material should be included in the assessment of comparable cases of damage in the course of insurance settlements.
Christoph Zekorn
Head of the Microscopic Analysis Laboratory
Material selection
for fastening systems
Problem: Material selection with regard to service life prediction
External influences such as temperature, atmospheric oxygen and UV radiation stress plastics, which initially impairs their usability and subsequently leads to component failure. For outdoor use, the material must be sufficiently stabilised. The long-term behavior of three polyethylene types (“I” to “III”) will be described for the purpose of material selection for outdoor fastening systems (without direct UV radiation).
Methodology: Material characterisation after accelerated ageing
- Accelerated ageing due to thermo-oxidative stress at higher temperatures in atmospheric oxygen
- Determination of the resistance to oxygen based on the residual stabilisation via the oxidation induction time (OIT)
- Detection of material damage due to oxidation using infrared spectroscopic analysis
- Mechanical failure behavior via the characteristic values modulus of elasticity, yield stress and elongation at yield (tensile tests)
Result: considerable deviations in terms of service life
This simple combination of thermal, spectroscopic and mechanical tests enabled the material to be qualified.
Dr. rer. nat. Sabine Standfuß-Holthausen
Head of the Spectroscopic Analysis Laboratory
Mechanical testing
of network components
Industry-specific testing and analysis services for plastic piping components and add-on fittings
Plastic components used in supply networks are examined and evaluated at the Center for Plastics Analysis and Testing (KAP). The mechanical testing laboratories provide very different test concepts:
- Torsional shear tests
- Tensile, compression and bending tests
- Hardness test
- Determination of impact strength
- Impact bending test at high load speeds
- Compression set tests on seals
- Creep behavior of pipe materials under the influence of media
- Leakage analysis of mechanically and medially loaded seals
- Investigation of fatigue behavior under dynamic load
- Long-term behavior of pipe materials under additional medial load
- Microscopic weld seam examinations (heat-affected zone, morphology, electrofusion distribution)
- Examination of screw and crimp connectors
In addition to plastics engineering DIN standards, specifications from industry-specific regulations according to DVGW and/or DVS are often used as the basis for the tests. In addition, solutions for individual testing tasks are available by means of adaptation to existing testing and analysis systems.
Methodology: Torsional shear tests to evaluate the weld seam quality by means of mechanical loading
Today, the connection of pipe and socket or add-on fitting is often made using plastic welding processes. The quality of the welded joints is verified in accordance with applicable guidelines by means of mechanical loading until failure in torsional shear tests. For this purpose, test specimens are machined out of the welded joint and twisted.
Result: Proof of perfect weld seam quality
Only a high-quality welded joint will lead to ductile failure in the base material of the joint under mechanical stress. Otherwise, a brittle separation of the joint surface indicates a defective weld, which can be the cause of faults in an otherwise safe operation of the supply networks.
Tobias Conen, M. Sc.
Head of the Mechanical Testing Lab
Investigation of
Building services piping
Problem: Welding defects on building services pipelines
The air conditioning of a new building was installed using plastic piping systems in hollow floors, suspended ceilings and under plaster. During the installation, approx. 20 kilometers of piping of various diameters were laid and connected to each other via several hundred welds. Apparent defects, particularly in the joints (butt and socket welding), suggested that the work had not been carried out professionally in accordance with the applicable DVS 2202 guideline.
Methodology: Building inspection and microscopic thin section examinations
- On-site assessment of the construction object, including documentation and sampling of representative welded joints for laboratory tests
- Thin section preparation in the joining area of welded joints
- Polarisation microscopic examination of the thin sections
Result: insufficient joining quality
On site, some of the pipes showed serious angular deviations of up to 10° (permissible max. 2° according to assessment group “II”) in addition to weld misalignment. The marking of the prescribed pipe insertion depth (socket welds) was missing in the entire pipe network. Furthermore, inadmissible deviations from the applicable installation guidelines were evident (installation under mechanical tension / pipe fixing points / creation of compensating bends).
The microscopic examinations revealed some large cavities in the joint area, which are a sign of poor welding. A permanent joint strength is not to be expected.
Christoph Zekorn
Head of the Microscopic Analysis Laboratory