Prasun Majumdar

Full-Field Measurements for Determining Orthotropic Elastic Parameters of Woven Glass-Epoxy Composites Using Off-Axis Tensile Specimens

Using theoretical formulations to describe the general response of an orthogonally woven glass-epoxy composite subjected to off-axis tension loading, a simple experimental methodology incorporating stereovision and 3D digital image correlation (3D-DIC) into several optimization procedures is described that provides a direct approach for quantitatively determining all of the elastic properties. During each off-axis tensile loading experiment, axial strains are determined using both mechanical extensometry and 3D-DIC, with the 3D-DIC measurements also used to extract both the in-plane transverse normal strain and the shear strain fields. The effectiveness of various optimization procedures are then evaluated and compared by performing a series of off-axis tensile loading experiments to determine the material engineering constants, including E1, E2, G12, and v12 for the nominally transversely isotropic material. Results indicate excellent agreement between the extensometer measurements and the average axial strain obtained by 3D-DIC. Furthermore, direct comparison of the proposed optimization methods indicates that each method is robust and effective, especially when employing 3D-DIC to extract additional information to complete the elastic property characterization procedure.

Effect of processing conditions and material properties on the debond fracture toughness of foam-core sandwich composites: experimental optimization

Abstract The structural performance and reliability of the foam-core sandwich composites are known to be dependent on the strength of the core–skin bonding. Mechanical tests have repeatedly demonstrated that the failure modes for the sandwich during flexural, compression, and tension loading are first triggered by the failure of the interface or the sub-interface zones between the core and the skin. Once this failure mode sets in, core shear and delamination progress rapidly, leading to the final failure of the sandwich construction. The strength of the core–skin bonding depends on the chemical reactions taking place during the cure process. The effect of processing parameters and material properties on the core–skin bonding strength were investigated experimentally. The skin–core debond fracture toughness was measured using Tilted Sandwich Debond specimens. Verifying the heuristics developed in the previous part of this paper [Srinivasagupta et al., Compos. Part A, in press], we achieved a 78% increase in debond fracture toughness with elevated temperature processing, and observed reduced variability with higher suction pressures. We also saw increase in debond fracture toughness with foam density, validating the assumption that interfacial bonding controls the debond fracture toughness. An increase in resin uptake with foam density was an interesting observation from these experiments.

Conformable tire patch loading for FRP composite bridge deck

Fiber-reinforced polymer (FRP) composites are increasingly being used in bridge deck applications. However, there are currently only fledgling standards to design and characterize FRP deck systems. One area that should be addressed is the loading method for the FRP deck. It has been observed that the type of loading patch greatly influences the failure mode of a cellular FRP deck. The contact pressure distribution of a real truck loading is nonuniform with more concentration near the center of the contact area as a result of the conformable contact mechanics. Conversely, the conventional rectangular steel patch on a FRP deck act like a rigid flat punch and produces stress concentration near the edges. A proposed simulated tire patch has been examined for loading a cellular FRP deck with the load distribution characterized by a pressure sensitive film sensor and three-dimensional contact analysis using ANSYS. A loading profile is proposed as a design tool for analyzing FRP deck systems for strength and dur...

Performance Evaluation of FRP Composite Deck Considering for Local Deformation Effects

We examine here the replacement of a deteriorated concrete deck in the historic Hawthorne Street Bridge in Covington, Va. with a lightweight fiber-reinforced polymer (FRP) deck system (adhesively bonded pultruded tube and plate assembly) to increase the load rating of the bridge. To explore construction feasibility, serviceability, and durability of the proposed deck system, a two-bay section (9.45 by 6.7 m ) of the bridge has been constructed and tested under different probable loading scenarios. Experimental results show that the response of the deck is linear elastic with no evidence of deterioration at service load level (HS-20). From global behavior of the bridge superstructure (experimental data and finite- element analysis), degree of composite action, and load distribution factors are determined. The lowest failure load ( 93.6 kips or 418.1 kN ) is about 4.5 times the design load ( 21.3 kips or 94 kN ), including dynamic allowance at HS-20. The failure mode is consistent in all loading conditions ...

Effect of processing conditions and material properties on the debond fracture toughness of foam-core sandwich composites: process model development

Vacuum assisted resin infusion molding (VARIM) is a recently developed promising low-cost batch process that has been applied to the manufacture of large-sized composite parts. The process has been successfully extended to the construction of foam-core sandwich composites by introducing a co-injection resin transfer molding (CIRTM) technique. In the CIRTM process, the sandwich is manufactured in one integral step and the bonding between the skin and the core is developed during the cure process. The structural performance and reliability of these sandwiches are dependent on the strength of the core-skin bonding. Processing conditions and material parameters such as permeability of fibers and foam; viscosity and cure kinetics of the resin; and resin infusion pressure and temperature all affect the cure. A rigorous 3D non-isothermal processing model was developed for the first time to assist in the design and optimization of the CIRTM process for sandwich construction. A simplified 1D isothermal model was also developed for real-time control and compared with the full-blown model. The effects of various processing parameters on the core-skin bonding strength were investigated with parametric studies. Based on these studies using the processing models, we develop heuristics for optimizing application-relevant parameters of the sandwich composites.

Nonlinear anisotropic electrical response of carbon fiber-reinforced polymer composites

Composites materials are often subjected to multi-physics conditions in different applications where, in addition to mechanical loads, they also need to sustain other types of loads such as electrical currents. Composite materials have heterogeneous electrical properties at the local level that can be different at the global level. In this study, electrical response was measured to explore how different lamina orientation and electrical current density affect anisotropic electrical properties of composite. For in-plane study, current was applied up to 80 kA/m2 for both unidirectional and quasi-isotropic composite. In thickness direction, maximum current density was 6 kA/m2. As expected, electrical properties are indeed dependent on fiber architecture which acts as conduction path in the laminate, and also depends on progressive increase in current density. Anisotropic electrical behavior was measured experimentally and the threshold of nonlinear behavior due to high current was identified. Threshold current density for unidirectional composite in fiber direction and for quasi isotropic are, respectively, 48.14 ± 4.3% kA/m2, 56.06 ± 4.4% kA/m2. For off-axis fiber laminates, this threshold limit shifts from 34.36 ± 5.9% kA/m2 to a lower value of 17.95 ± 7.9% kA/m2 as the fibers are oriented away from the x axis. In thickness direction, this threshold limit is in between 2.56 and 3.80 kA/m2. The electrical-thermal responses were also studied experimentally with thermography tests and the results were compared to indicate damage. A 3D X-ray microscope has been used to visualize and quantify (down to 1 micron) such local material state changes due to electrical current.

Development and application of an experimental system for the study of thin composites undergoing large deformations in combined bending–compression loading

To increase understanding of damage evolution in advanced composite material systems, stereo digital image correlation has been integrated with a compression–bending mechanical loading system to obtain full-field deformations on both compression and tension surfaces throughout the loading process. The integrated system is employed to simultaneously quantify full-field deformations along the length of the specimen. Specifically, the integrated system is employed to experimentally study the progressive failure behavior of thin, woven glass–epoxy composite specimens undergoing both cyclic and monotonic compression–bending loading resulting in large out-of-plane bending deformations with end conditions that allow free out-of-plane rotation. Experimental results obtained using the measurement system for specimens undergoing both linear and highly non-linear deformations during monotonic loading are presented. Results clearly show (a) the presence and magnitude of anticlastic (double) specimen curvature near mid-length for all fiber angles, (b) the distinct differences in the strain fields between the tension and compression surfaces at the critical location, (c) the corresponding disparity in local material failure mechanisms between the tension (e.g. matrix cracking) and compression (e.g. fiber buckling) surfaces in the critical regions and (d) the highly localized character of the strain fields, focused in regions of increased damage.

Fiber nonlinear predictive model for combined bending-compression loading of an orthogonal plane weave composite laminate structure

To increase understanding of damage evolution in advanced composite material systems, a series of large deflection bending-compression experiments and model predictions have been performed for a woven glass-epoxy composite material system. Theoretical developments employing both small and large deformation models and computational studies are performed. Results (a) show that the Euler–Bernoulli beam theory for small deformations is adequate to describe the shape and deformations when the axial and transverse displacement are quite small, (b) show that a modified Druckers equation effectively extends the theory prediction to the large deformation region, providing an accurate estimate for the buckling load, the post-buckling axial load-axial displacement response of the specimen and the axial strain along the beam centerline, even in the presence of observed anticlastic (double) specimen curvature near mid-length for all fiber angles (that is not modeled), and (c) for the first time the quantities σeff – ɛeff are shown to be appropriate parameters to correlate the material response on both the compression and tension surfaces of a beam-compression specimen in the range 0 ≤ ɛeff < 0.005 as the specimen undergoes combined bending-compression loading. In addition, computational studies indicate that the experimental σeff – ɛeff results are in reasonable quantitative agreement with unwoven laminate finite element simulation predictions in the range 0 ≤ ɛeff < 0.010, with the effect of the woven structure appearing to provide the key constraint for various fiber angles that leads to the observed consistency in the experimental σeff – ɛeff results on both surfaces.

Multi-physics Response of Structural Composites and Framework for Modeling Using Material Geometry

Structural composite materials are now being engineered with increasingly complex heterogeneous morphology to achieve multi-functionality and reliable performance in extreme environments. Therefore, bulk response of material is inherently dependent on local morphology. Prognosis of structural composites via simulation (virtual or digital twin) will require understanding and mathematical representation of fundamental mechanisms of such interactions for a variety of service conditions. Although progress has been made regarding prognosis of material state changes due to mechanical loading, their synergistic response in a multi-physical environment is not fully understood. As a first step to address this broader scientific challenge, this paper examines how multi-physical environment (such as electrical field) causes microstructural changes in structural composites and hence may affect structural performance. Preliminary results show that increasing magnitude of electrical current can cause significant degradation. On the other hand, multi-physical behavior depends on local microstructure and resulting anisotropic nature of composite material. Details of expreimnetal procedure, results and a framework for future modeling approaches has been reported.

3D Self‐Architectured Steam Electrode Enabled Efficient and Durable Hydrogen Production in a Proton‐Conducting Solid Oxide Electrolysis Cell at Temperatures Lower Than 600 °C

Abstract Hydrogen production via water electrolysis using solid oxide electrolysis cells (SOECs) has attracted considerable attention because of its favorable thermodynamics and kinetics. It is considered as the most efficient and low‐cost option for hydrogen production from renewable energies. By using proton‐conducting electrolyte (H‐SOECs), the operating temperature can be reduced from beyond 800 to 600 °C or even lower due to its higher conductivity and lower activation energy. Technical barriers associated with the conventional oxygen‐ion conducting SOECs (O‐SOECs), that is, hydrogen separation and electrode instability that is primarily due to the Ni oxidation at high steam concentration and delamination associated with oxygen evolution, can be remarkably mitigated. Here, a self‐architectured ultraporous (SAUP) 3D steam electrode is developed for efficient H‐SOECs below 600 °C. At 600 °C, the electrolysis current density reaches 2.02 A cm−2 at 1.6 V. Instead of fast degradation in most O‐SOECs, performance enhancement is observed during electrolysis at an applied voltage of 1.6 V at 500 °C for over 75 h, attributed to the “bridging” effect originating from reorganization of the steam electrode. The H‐SOEC with SAUP steam electrode demonstrates excellent performance, promising a new prospective for next‐generation steam electrolysis at reduced temperatures.