Full Generic Qualification of Nylon 12 Carbon Fiber Composite for Dynamic Thermoplastic Composite Pipe and Hybrid Flexible Pipe Applications

Composite structures are used as corrosion insensitive load bearing reinforcement in dynamic Thermoplastic Composite Pipe (TCP) and Hybrid Flexible Pipe (HFP) applications. The qualification of such structures can follow different strategies: product level versus material characterization. DNVGL-ST-F119 proposes a generic knowledge-based approach based on a testing pyramid. The pyramid allows a generic material characterization for a large number of conditions. Testing of dedicated specimens in constant media exposure measures the actual properties and changes of the material. Regression data is obtained for end-of-life properties. Simulations can be conducted using these properties to determine performance of the product in any state and condition and validate any load cases through classical stress combination. The characterization for VESTAPE® Nylon 12 Carbon Fiber thermoplastic composite (CF-PA12) covers all failure mechanisms for matrix, fiber and interface in static, dynamic and stress rupture mode for virgin, fully hydrocarbon saturated and aged to end of life in saturated condition. Each condition assessment is carried out in complete temperature dependency for subzero, room temperature, intermediate and maximum use temperature of 176°F (80°C). Fatigue testing covers runtimes of 106 cycles whereas stress rupture assessment exceeds 12,500h which corresponds to almost 1.5 years. With dense data populations for both regression curves and static test results the coefficient of variation is controlled. All characterization logic and data are analyzed for validity and certified by the official body of the DNV-GL. The material characterization enables simulation of a variety of application designs in predictive engineering and a simplified study is made for a dynamic gas injection jumper to demonstrate relevant occurring load cases. Utilizing all data and approaches allows to define the overall application envelope of the material. For the case of the thermoplastic composite of CF-PA12 it covers static flowlines, dynamic jumpers, service lines up to dynamic risers in sour crude service up to 176°F (80°C). The knowledge-based approach allows for economic design in engineering cases without compromising safety.

The onset of the frictional motion of dissimilar materials

Frictional motion between contacting bodies is governed by propagating rupture fronts that are essentially earthquakes. These fronts break the contacts composing the interface separating the bodies to enable their relative motion. The most general type of frictional motion takes place when the two bodies are not identical. Within these so-called bimaterial interfaces, the onset of frictional motion is often mediated by highly localized rupture fronts, called slip pulses. Here, we show how this unique rupture mode develops, evolves, and changes the character of the interface’s behavior. Bimaterial slip pulses initiate as “subshear” cracks (slower than shear waves) that transition to developed slip pulses where normal stresses almost vanish at their leading edge. The observed slip pulses propagate solely within a narrow range of “transonic” velocities, bounded between the shear wave velocity of the softer material and a limiting velocity. We derive analytic solutions for both subshear cracks and the leading edge of slip pulses. These solutions both provide an excellent description of our experimental measurements and quantitatively explain slip pulses’ limiting velocities. We furthermore find that frictional coupling between local normal stress variations and frictional resistance actually promotes the interface separation that is critical for slip-pulse localization. These results provide a full picture of slip-pulse formation and structure that is important for our fundamental understanding of both earthquake motion and the most general types of frictional processes.

Linking geodynamic subduction models to self-consistent 3D dynamic earthquake rupture and tsunami simulations

<p>3D imaging reveals striking along-trench structural variations of subduction zones world-wide (e.g., Han et al, JGR 2018). Subduction zones include basins, sediments, splay and back-thrusting faults that evolve over a large time span due to tectonic processes, and may crucially affect earthquake dynamics and tsunami genesis. Such features should be taken into account for realistic hazard assessment. Numerical modeling bridges time scales of millions of years of subduction evolution to seconds governing dynamic earthquake rupture, as well as spatial scales of hundreds of kilometers of megathrust geometry to meters of an earthquake rupture front.</p><p>Recently, an innovative framework linking long-term geodynamic subduction and seismic cycle models to dynamic rupture models of the earthquake process and seismic wave propagation at coseismic timescales was presented (van Zelst et al., JGR 2019). This workflow was extended in a simple test case to link the 2D seismic cycle model to a three-dimensional earthquake rupture mode, which was then linked to a tsunami model  (Madden et al., EarthArxiv, doi:10.31223/osf.io/rzvn2). Here, we couple a 2D seismic cycle model to 3D earthquake and tsunami models and assess the geophysical aspects of this coupling. We extract all 2D material properties, stresses and the strength of the megathrust, and its geometry, from the seismic cycling model at a time step right before a typical megathrust event to use as initial conditions for the 3D dynamic rupture models. We explore the effects of along-arc variations of megathrust curvature, sediment content, and closeness to failure of the wedge on earthquake dynamics by studying the effects on slip, rupture velocity, stress drop and seafloor deformation.</p><p>In a next step, the dynamic seafloor displacements are linked to tsunami simulations that use depth-integrated (hydrostatic) shallow water equations. This approach efficiently models wave propagations and large-scale horizontal flows. We also present novel, fully coupled 3D dynamic rupture-tsunami simulations (Krenz et al., AGU19; Abrahams et al., AGU19; Lotto and Dunham et al., 2015, Computational Geosciences) which solve simultaneously for the solid earth and ocean response, taking gravity into account via a modified free surface boundary condition.</p><p>Earthquake rupture modeling and the fully-coupled tsunami modeling utilize SeisSol (www.seissol.org), a flagship code of the ChEESE project (www.cheese-coe.eu). SeisSol is an open source software package using unstructured tetrahedral meshes that are optimally suited for the complex geometries of subduction zones. The here presented links between geodynamic subduction and seismic cycling model with earthquake dynamics and tsunami models better account for the complexity of subduction zones and help evaluate the effects of along arc heterogeneities on earthquake and tsunami behavior and advance physics-based assessments of earthquake-tsunami hazards.</p>

The role of the fault-block structure of the continental margin in the generation of the strongest subduction earthquakes

<p>Modern seismotectonic studies are aimed at obtaining a self-consistent explanation of fault zone heterogeneity, the rupture process, recurrence times and rupture mode of large earthquake sequences. In subduction regions large earthquakes are often characterized by very long source zones and complex long-term postseismic processes following the coseismic release of accumulated elastic stresses. A set of mechanical models was proposed to describe the generation of strongest earthquakes based on the idea of the synchronous failure of several adjacent asperities.</p><p>In this study we propose a model which is based on verified numerical schemes, which allows us to quantitatively characterize the process of generation of strong earthquakes. The model takes into account the fault-block structure of the continental margin and combined the ideas of a possible synchronous destruction of several adjacent asperities, mutual sliding along a fault plane with a variable coefficient of friction and subsequent healing of medium defects under high pressure conditions.</p><p>The applicability of the proposed model is shown by the example of the recent seismic history of the Kuril subduction zone. Kuril island arc is one of the most tectonically active regions of the world due to very high plate convergence rate. Heterogeneities in the mechanical coupling of the interplate interface in this region lead to the formation of the block structure of the continental margin, which is confirmed by various geological and seismological studies.</p><p>GPS observations recorded at different stages of seismic cycle related to the 2006–2007 Simushir earthquakes allow us to model geodynamic processes of slow strain accumulation and its rapid release during the earthquake and the subsequent posteseismic process. We use parameters describing the regional tectonic structure and rheology obtained from the inversion of geodetic data to construct a 2D model of generation of large earthquakes in central Kurils. Analysis of paleoseismic data on dates and rupture characteristics of previous major earthquakes shows a good agreement between the modeled and observed seismic cycle features. The predicted horizontal displacements of the seismogenic block at the coseismic stage are consistent with satellite geodetic data recorded during the 2006 Simushir earthquake.</p><p>The proposed model provides new insights into the geodynamic processes controlling the occurrence of strong subduction earthquakes.</p>

Flexural behavior of hybrid GFRP - concrete railway sleepers

This paper aims to present the flexural behavior of hybrid GFRP (glass fiber reinforced polymer) concrete beams as sleepers to railway application. It was tried to obtain sleepers with adequate mechanical resistance, not susceptible to corrosion, durable and lighter than the sleepers in prestressed concrete. Pultruded fiberglass and polyester resin profiles were filled with high strength concrete and polyolefin fiber in the following proportions by volume: 1% and 2.5%. The beams were 1.06 meters long and had a 76 mm x 76 mm x 6 mm cross section, corresponding to a reduced model in a 1: 2.64 scale of a 2.80 meters long sleeper. In the bending tests, the load was applied at the center of the sleeper, as provided in the Brazilian standard NBR 11709 (2015) and American standard AREMA (2016). During the tests the applied load, the vertical deflection and the longitudinal tensile and compression deformations were measured in the center of the span. The influence of fiber addition on the strength, rupture mode and flexural modulus of elasticity of the hybrid beams was analyzed. Finally, the hybrid sleeper performance was compared to that of the prestressed concrete monoblock sleeper. The results obtained were satisfactory, indicating that the proposed hybrid sleeper is a constructively and technically feasible alternative.

Analysis of rupture mode and acoustic emission characteristic of rock and coal samples with holes

In order to understand the rupture mechanism of rock and coal samples with holes, the acoustic emission (AE) tests of rock and coal samples with holes under uniaxial compression are done. Through the AE tests, the basic mechanical and AE variation rule of two samples in the total rupture process are obtained, the dynamic rupture process was observed and finally the spatial evolution and multi-fractal characteristic of AE are analyzed. The results show that the variation rule of AE events of two samples are coincident with the variation rule of stress. The uniaxial compressive strength of a rock sample with a hole is about five times than that of a coal sample with a hole, and the maximum AE pulsing counts (AEPC) of a rock sample with a hole is much larger than that of a coal sample with a hole. Due to the variation of lithology, the dynamic rupture process and the spatial evolution rule of AE events of rock and coal samples with holes are obviously different. But the distributions of the three-dimensional locations of the two samples are coincident with the macroscopic rupture morphology. Both of them have multi-fractal characteristic in the process of rupture, the multi-fractal spectrum width Δf(α) at the time of rupture is smaller than that before rupture and the Δf(α) before rupture is smaller than that after rupture. This indicates that the energy (E) before and after rupture is smaller than that at the time of rupture, the E after rupture is smaller than that before rupture and the E of a coal sample with a hole in each stage is less than that of the corresponding stages of a rock sample with a hole.

Enabling sequential rupture for lowering atomistic ice adhesion

Embedding the intrinsic sequential rupture mode into surfaces as an interfacial mechanical function can lead to low atomistic ice adhesion strength.

Impact Toughness of Closed-Cell Aluminum Foam

The impact toughness of closed-cell aluminum foam with various densities was investigated. The impact load history revealed an elastic region followed by a rapid load drop region. The peak load and impact toughness of aluminum foam increases exponentially with density. The power exponents for impact toughness test are greater than that for compressive test. Fracture analysis indicated a mixed-rupture mode of quasi-cleavage and small shallow dimples. It can be attributed to the complex state of stress of notched specimens and elevated impact velocity under impact loading.