A new engineering approach to predict the hydrostatic strength of uPVC\ud pipes

Extruded unplasticised Poly(Vinyl Chloride) (uPVC) pipes are certified using pressurised pipe tests.\ud During these tests the pipes are subjected to a certain temperature and internal pressure, while the\ud time-to-failure, the time at which the internal pressure drops due to rupture or fracture, is measured.\ud These tests are time consuming and are therefore costly. To circumvent these costs a model-based\ud approach is proposed where the time-to-failure is predicted. The input parameters for this approach\ud can be determined using short term measurements. The approach uses the observation that the timeto-\ud failure kinetics of uPVC pipes subjected to an internal pressure is independent of the type of failure\ud mode (ductile, semi-ductile or brittle). This supports our statement that the underlying mechanism\ud that initiates failure is similar for these types of failure. Local deformation of the material up to a\ud critical value of the anelastic strain is believed to determine the start of failure of the material. This\ud critical strain appears to be constant for the testing conditions used during this study. A pressure\ud modified Eyring expression is employed to calculate the strain rate resulting from the applied stress\ud at a certain temperature. The time-to-failure follows from the calculated strain rate and the critical\ud strain of the material. This approach has been verified against literature data and shown to hold\ud quantitatively. Furthermore, the model seems to hold for different processing conditions

A new engineering approach to predict the long-term hydrostatic strength of unplasticized poly(vinyl chloride) pipes

Extruded polymer pipes are qualified using pressurized pipe tests. With these tests the long-term hydrostatic strength is determined by subjecting the pipes to an internal pressure, while measuring the time-to-failure. Although these tests can be accelerated (at higher temperatures), they remain time consuming and require a spacious experimental setup. To circumvent this costly method a model based approach is proposed by which the long-term hydrostatic strength is predicted. Using short term measurements, the input parameters for this approach can be determined. In this engineering approach the effects of physical aging are included. The approach is capable to quantitatively predict the (long-term) failure time of pipe sections under internal pressure

Friction Surface Cladding of AA1050 on AA2024-T351; influence of clad layer thickness and tool rotation rate

Friction Surfacing Cladding (FSC) is a recently developed solid state process to deposit thin metallic clad layers on a substrate. The process employs a rotating tool with a central opening to supply clad material and support the distribution and bonding of the clad material to the substrate. The tool is held at a given distance above the substrate and translates relative to the substrate while the clad material is pressed out and deposited. This work studies the effect of the tool rotation speed and the clad layer thickness on the deposition quality of AA1050 clad layers on top of AA2024-T351 substrates at constant process temperatures. Well bonded, defect free clad layers with uniform thickness and width are produced. A 2D axisymmetric thermal-flow model predicts the influence of the process parameters and confirmed the experimental observations

Condition monitoring of uPVC gas pipes

No abstract

Cyclic shear behavior of austenitic stainless steel sheet

An austenitic stainless steel has been subjected to large amplitude strain paths containing a strain reversal. During the tests, apart from the stress and the strain also magnetic induction was measured to monitor the transformation of austenite to martensite. From the in-situ magnetic induction measurements an estimate of the stress partitioning among the phases is determined. When the strain path reversal is applied at low strains, a classical Bauschinger effect is observed. When the strain reversal is applied at higher strains, a higher flow stress is measured after the reversal compared to the flow stress before reversal. Also a stagnation of the transformation is observed, meaning that a higher strain as well as a higher stress than before the strain path change is required to restart the transformation after reversal. The observed behavior can be explained by a model in which for the martensitic transformation a stress induced transformation model is used. The constitutive behavior of both the austenite phase and the martensite is described by a Chaboche model to account for the Bauschinger effect. In the model mean-field homogenization of the material behavior of the individual phases is employed to obtain a constitutive behavior of the two-phase composite. The overall applied stress, the stress in the martensite phase and the observed transformation behavior during cyclic shear are very well reproduced by the model simulations

Annealing of SnO2 thin films by ultra-short laser pulses

Post-deposition annealing by ultra-short laser pulses can modify the optical properties of SnO2 thin films by means of thermal processing. Industrial grade SnO2 films exhibited improved optical properties after picosecond laser irradiation, at the expense of a slightly increased sheet resistance [Proc. SPIE 8826, 88260I (2013)]. The figure of merit ϕ = T10 / Rsh was increased up to 59% after laser processing. In this paper we study and discuss the causes of this improvement at the atomic scale, which explain the observed decrease of conductivity as well as the observed changes in the refractive index n and extinction coefficient k. It was concluded that the absorbed laser energy affected the optoelectronic properties preferentially in the top 100-200 nm region of the films by several mechanisms, including the modification of the stoichiometry, a slight desorption of dopant atoms (F), adsorption of hydrogen atoms from the atmosphere and the introduction of laser-induced defects, which affect the strain of the film