Browsing by Author "Reyes, Sergio I."

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    Development of a pressure-, velocity-, and acceleration-dependent phenomenological friction model using experimental data of sliding tests between 11 polymers and stainless steel
    (2024) Tapia, Nicolas F.; Reyes, Sergio I.; Vassiliou, Michalis F.; Almazan, Jose L.
    This paper experimentally investigates the frictional behavior between stainless steel and 11 polymers. Particularly, the dependence of the friction coefficient on the sliding velocity, pressure, and acceleration is quantified. The novelty of this work lies in quantifying the acceleration-dependent nature of friction, correlating it to the well-documented Stick-Slip effect. The experimental setup consisted of two parallel stiff steel beams, one above the other, with a separation of 95 mm, and steel surfaces welded at the inner sides for sliding the polymers. Cylindrical polymer pads were placed between the stainless-steel surfaces and connected to a dynamic actuator to apply the displacement protocol. The protocol consisted of consecutive nominally constant-velocity ramp cycles covering velocities from 1 mm/s to 300 mm/s (with 20 mm/s increments). An additional vertical force was applied with a hydraulic actuator to reach nominal pressures in the polymers between 5 and 80 MPa. The results showed that the friction coefficient depends on the velocity, pressure, and acceleration of the motion, and a phenomenological model on these three variables is proposed. The velocity dependence can be represented through a logarithmic relationship, while the pressure dependence is through an exponential decay relationship. The acceleration dependence was represented through a linear relationship, which could capture the stick-slip effect. Overall, this work contributes to a better understanding of friction for seismic isolation systems. Since friction is the main source of energy dissipation in such structures, the proposed model will allow a higher accuracy in predicting variables of interest during the dynamic analyses of seismically isolated structures with frictional systems.
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    Experimental validation of an energy-dissipating anchoring system for continuously-supported storage tanks
    (2023) Tapia, Nicolas F.; Almazan, Jose L.; Valdebenito, Nathaly; Reyes, Sergio I.
    This paper presents a novel energy dissipation device called NWS-TADAS and its experimental validation. The device was inspired by the flexural failure of the top plate of anchor bolt chairs in wine storage tanks observed after the 2015 Mw 8.3 Illapel, Chile Earthquake. The device is proposed to replace traditional anchors in continuously-supported storage tanks. This device provides advantages compared to other steel dampers in terms of constructability and force-deformation relationship. TADAS and similar steel energy-dissipation devices have a relatively high constructive difficulty derived from their welding process. The proposed device has no welds on the dissipation plate, hence its nomenclature (Non-Welded Symmetrical TADAS). In addition, design deformations are not chosen consistently with the total failure energy for the expected number of cycles during its lifetime, resulting in non-optimal devices (underutilized). Full-scale specimens were manufactured in AISI-304 stainless steel and ASTM-A36 steel and tested under two types of displacement protocols. Both materials were chosen because they are the most used for tanks in the food industry and industrial storage. The results showed that A36 carbon steel presented a smaller hardening. In all cases, the plastic deformations on the surface of the dampers were not uniform as expected in triangle-shape devices, being concentrated at the center and close to the embedment zone and causing a premature fatigue failure. The dissipated energy for consecutive cycles was stable, and using additional stacked dampers in the system had no significant effects on the hysteretic behavior. The system showed no rate dependence. The dampers presented almost identical force-deformation relationships for two consecutive earthquakes; the dissipated energy was less than 20% of their total capacity. The latter result validates their capacity to withstand several earthquakes without being replaced, further concluding that the NWS-TADAS is a viable alternative to be implemented as an anchoring system on storage tanks and other types of structures. Finally, it is concluded that performing testing protocols defined with a statistical approach may be more meaningful for dampers subject to earthquake demands.
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    Validation of a three-dimensional finite element constitutive modeling approach for a thermoplastic polyurethane calibrated with uniaxial tests
    (2025) Reyes, Sergio I.; Lopez, Edgar L.; Vassiliou, Michalis F.
    This paper presents the three-dimensional finite element constitutive modeling validation for a Thermoplastic Poly-Urethane (TPU) material. The material parameters are those given in a previous study obtained by calibrating the constitutive model with uniaxial material-level test results (1-D tensile and compression tests). Confined compression tests were performed to estimate the bulk modulus for more accurate material characterization. The parameters were validated by comparing the results of experimental tests on TPU components with those obtained by its equivalent finite element simulations. The TPU component tests comprised cyclic compression tests of (i) a TPU cylinder, (ii) a solid 100 mm diameter TPU ball, and (iii) a 100 mm diameter TPU ball with an 80 mm steel core. In all tests, the constitutive model parameters showed an excellent performance in representing the mechanical behavior of the material observed in the tests, including the nonlinear stiffness and hysteresis. Finally, a briefcase study is presented to illustrate the applicability of the validated constitutive model parameters in modeling a novel TPU damper for structural control before its manufacturing and experimental testing. The validated constitutive modeling approach and available material parameters will allow the performance of reliable and early-stage finite element simulations to prototype the mechanical behavior of TPU components of different shapes and boundary conditions and thus gain relevant insight into the component level response before manufacturing and testing.