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Infusible thermoplastic Elium® family of resins from Arkema have garnered much attention in recent years as a possible replacement for thermoset resins in laminate and sandwich composite manufacturing for wind blade applications due to its ease of recyclability and the ability to utilize existing manufacturing processes without imposing complicated variations. However, physical and mechanical properties of the proposed Elium® based thermoplastic composites must be comparable to existing epoxy (thermoset) based composites using manufacturing processes relevant for large wind turbine blades. A 13-meter-long demonstration blade was manufactured for that purpose and sandwich samples were obtained from that project for a detailed study. This paper details three-point flexural properties of unidirectional E-glass fiber reinforced acrylic and epoxy based sandwich panels with identical balsa wood core materials. In addition, to evaluate the relative merit considering debond failure mode, the interfacial critical strain energy release rate, predominantly in mode-1, was compared via single cantilever beam testing. In sandwich composites constructed with balsa wood core material, resin uptake by the balsa core is traditionally impeded via the insertion of a scrim material at the facesheet to core interface. Results revealed that inclusion of scrim mesh layer at the facesheet to core interface reduced flexural properties and strain energy release rates in panels infused with acrylic resin but did not significantly reduce these properties in epoxy infused facesheets.

Sandwich structured (SS) composites demonstrate considerable flexural stiffness and high strength-to-weight ratios and can be tailored as functional materials. Historically they have been constrained to specific material types and geometry due to limitations in manufacturing methods. However, employing additive manufacturing (AM), specifically direct ink writing (DIW), can provide an alternative method for making SS composites with complex and controllable micro and mesostructures with multifunctionality targeted at desired mechanical, thermal, and electrical properties. DIW, an extrusion-based AM technique, uses a viscous and thixotropic ink with desired components that, once printed, is cured to obtain the final complex net shape parts. In this paper, a novel hybrid AM technique is employed to manufacture SS composite materials containing bisphenol A-based epoxy core and carbon fiber reinforced polymer (CFRP) face sheets that are fabricated via DIW and vacuum infusion process (VIP), respectfully. We demonstrate that the fabrication of these SS composites can be tailored from a thermosetting material, from which additives and/or various lattice structures can be manufactured to achieve enhanced and desirable mechanical integrity with functional properties. Surface topology and mechanical testing techniques are used to characterize the fabricated hybrid SS composites to study and assess mechanical stability. A rheo-kinetic cure model was developed for the core material to allow for additive manufacturing process requirements while ensuring complete cross-linking for the thermoset-based core material. Because of the ability to obtain relatively small core-thickness and controlled architecture, this method now allows for fabricating layered micro-sandwich structures for realizing further light-weighting in relevant applications.

Carbon fiber-reinforced concrete as a structural material is attractive for civil infrastructure because of its light weight, high strength, and resistance to corrosion. Ultra-high performance concrete, possessing excellent mechanical properties, utilizes randomly oriented one-inch long steel fibers that are 200 microns in diameter, increasing the concrete’s strength and durability, where steel fibers carry the tensile stress within the concrete similar to traditional rebar reinforcement and provide ductility. Virgin carbon fiber remains a market entry barrier for the high-volume production of fiber-reinforced concrete mix designs. In this research, the use of recycled carbon fiber to produce ultra-high-performance concrete is demonstrated for the first time. Recycled carbon fibers are a promising solution to mitigate costs and increase sustainability while retaining attractive mechanical properties as a reinforcement for concrete. A comprehensive study of process structure–properties relationships is conducted in this study for the use of recycled carbon fibers in ultra-high performance concrete. Factors such as pore formation and poor fiber distribution that can significantly affect its mechanical properties are evaluated. A mix design consisting of recycled carbon fiber and ultra-high-performance concrete was evaluated for mechanical properties and compared to an aerospace-grade and low-cost commercial carbon fiber with the same mix design. Additionally, the microstructure of concrete samples is evaluated non-destructively using high-resolution micro X-ray computed tomography to obtain 3D quantitative spatial pore size distribution information and fiber clumping. This study examines the compression, tension, and flexural properties of recycled carbon fibers reinforced concrete considering the microstructure of the concrete resulting from fiber dispersion.

Organosheet composite scrap made from polyphenylene sulfide reinforced with long recycled carbon fibers was reprocessed to produce compression molding compounds. No additional polymer was added to the process, making this a demonstration of closed-loop recyclability in composites manufacturing. The recyclate, produced by hammer-milling organosheet trimmings, was sieved and the resulting particulate geometry was measured to predict the fiber length in the molded composites. Tensile testing of the composites revealed that high stiffness parts (tensile modulus greater than 13 GPa) can be achieved using particulate molding compounds, but that tensile strength was significantly degraded. Still, the isotropic molded composites exhibited a greater than 18.8% increase in tensile strength over the neat polymer. Evaluation of the composite microstructure via optical microscopy revealed that fiber packing played a significant role in the tensile strength of the particulate composites, indicating that microstructural heterogeneity should be avoided to maximize the properties of composites made of recycled organosheet waste.

Good dispersion of compounded ingredients in a rubber formulation is important for mechanical performance. After mixing, certain materials can remain undispersed within the rubber matrix, which could lead to critical flaws, influencing performance according to the Griffith failure criteria. High resolution X-ray computed tomography (XCT) offers a unique opportunity to measure phase domain size and distributions. Fillers such as carbon black or silica can be differentiated from sulfur or zinc oxide, providing an opportunity to determine dispersion characteristics of the various phases. The XCT technique has become an important characterization tool for three-dimensional and higher dimension material science due to the availability of polychromatic micro-focus X-ray sources and efficient high spatial resolution detectors with superior scintillators. High resolution XCT provides very rich data quantifying mixing efficiency of particulates in a matrix, such as insoluble sulfur or silica particles in rubber. Imaging with X-rays provides attenuation, phase, or scattering contrast and will prove to be a critical method for evaluating the field of rubber crosslinking, considering realistic environments in situ. This paper highlights methodology development and validation and provides insight on the dispersion of polymeric (insoluble) sulfur in rubber formulations. Dispersion assessment is compared using three techniques: high resolution XCT, population survival analysis in tensile testing, and optical microscopy.

In this study, wide- and small-angle scattering (WAXS, SAXS) are used to analyze the structure of polyacrylonitrile (PAN) carbon fiber. Wide angle scattering is used to identify lattice parameters such as d-spacings, stacking height of crystalline planes (Lc), average crystallize size (Lc), and various other features (void content, degree of graphitization). Small angle scattering results show orientation and size distributions of pores/amorphous regions. Several analysis techniques were applied to small angle scattering results to ensure accuracy. XRD Data collected is correlated to single fiber mechanical properties and a fiber model is developed. Fiber modulus is heavily related to crystallite dimensions and orientation as well as pore structure. Authors hypothesize that the non-linear elasticity observed in the fiber direction of carbon fibers arises from elastic planar motion within turbostratic carbon. As crystalline regions grow and expand, the lattice structure improves lowering the barriers for (002) quasi-graphene plane motion. This miniscule elastic planar motion can lead to a large nonlinear response to tensile loading especially for high crystallinity carbon fibers and underlying deformation mechanics is addressed considering transverse-isotropy of turbostatic graphite crystals.

The integration of repurposed and recycled carbon fibers into high-performance composites is essential to the adoption of composites for automotive structures due to their low-cost, high formability, and reduced environmental impact. When high areal density nonwovens of these fibers are infused with a semi-crystalline thermoplastic resin, organosheets offering competitive mechanical properties can be produced. This study examined the optimization of such composites through multiscale material characterization and post-process annealing. Single fiber tensile tests were used to characterize repurposed and recycled fiber formats. The thermomechanical properties of the polyphenylene sulfide matrix and resulting composites subjected to different post-process annealing conditions were characterized using differential scanning calorimetry, dynamic mechanical analysis, and nano-indentation. Single fiber push-in testing was conducted to evaluate the fiber–matrix interface as a function of annealing. It was shown that statistical methods based on the bootstrap principle successfully identify the effects of post-process annealing, which are otherwise masked by material inhomogeneity. Post-process annealing was shown to be an effective method of improving the resulting mechanical properties of repurposed and recycled carbon fiber organosheet composites, thereby optimizing their properties for use as a high-performance automotive structural material.

Epoxy-sized textile-grade polyacrylonitrile (PAN) carbon fiber (TCF) with 450 K filaments (CFTF, ORNL) was reinforced in the polycarbonate (PC) matrix using a compression molding technique. The epo...

Extensive particle fracture has been noticed in projectile penetration tests. However current models for predicting projectile penetration depths do not consider particle fracture. Therefore, in order to understand the role of particle shape on single grain strength and the subsequent comminution process, single grain crushing tests on sand grains of different shapes and sizes were performed. High-resolution, three dimensional images of grain surface, were created using confocal microscope and fracture of the grains were captured with high-speed imaging. Acoustic emissions during single grain crushing was used to estimate the energy released during grain fracture. It was found that local stress fields influence particle strength and in natural granular material surface flaws maybe the critical flaw causing fracture. The estimated critical flaw size causing fracture were submicron in size. The mass specific fracture energy increased with increasing failure stress and decreasing particle size and is significantly greater than that computed from pure diametrical breaking. Except for large angular grains, mass specific energies for different shapes were similar. Angular sands required multiple events to break. The outcome of this work can be utilized in geomechanics to understand the comminution process and in power industry to estimate the energy required for comminution.

For naval applications, composite sandwich structures are of significant interest, and are often manufactured using thin (2 to 4 mm) composite facings made from carbon or glass fiber reinforcement, attached to a thick (25 to 50 mm) section of PVC cellular foam or balsa wood-based core materials using a suitable polymeric resin. In the present study, we focus on the hygrothermal effect on the fiber-dominated compression properties of carbon fiber reinforced vinyl ester resin based polymeric composite (CF/VE), used as “skin” for a polymeric composite sandwich material. Hygrothermal conditioning is achieved by saturating samples in simulated seawater at 40°C. Compression properties are evaluated for coupons extracted along warp and fill undergoing- no conditioning, conditioning till saturation (up to 6 months), and long-term conditioning (2 years). Sea-water saturation yields in up to 12% drop in compression strength with a further 3–4% drop resulting from long-term conditioning. No statistically significant modulus degradation is noticed due to short or long-term hygrothermal exposure. The failure mechanism of the warp extracted coupon, which fails in a splitting failure mode originating due to the delamination between the 0/90 interface, or the fill extracted coupon, which fails due to the instability caused by tow micro-buckling, remains unchanged due to combined exposure (short or long-term) of seawater and temperature. The loss in strength is attributed to the degradation of the fiber-matrix interface, which is validated via conducting single fiber push-in tests with a nominal diameter of 7 micron for conditioned and unconditioned coupons.

The present paper addresses the influence of shape, size, and frictional characteristics of granular materials by utilizing X-ray computed tomography (CT) imaging and FEM. High-fidelity tri...

Stress–strain and volume change behavior for clean sands which have distinct particle shape (rounded and angular) with very similar chemical (mineralogical) composition, size, and texture in one-dimensional (1D) compression and drained triaxial compression are presented. The effect of particle morphology on the crushing behavior in one-dimensional loading is explored using laser light diffraction technique which is suitable for particle crushing because of its high resolution and small specimen volume capability. Particle size distribution in both volume/mass and number distributions are considered for improved understanding associated with the process of comminution. Number distributions present a clearer picture of particle crushing. It is argued that particle crushing in granular assemblies initiates in larger particles, rather than in smaller particle. It was found that rounded sand specimens showed greater crushing than angular sand specimens with higher uniformity coefficient. In 1D compression, loose specimens compress approximately 10% more than dense specimens irrespective of particle shape. Densification of angular sand results in improvement in stiffness (approximately 40%) and is comparable to that of loose rounded sand. In general, density has a greater influence on the behavior of granular materials than particle morphology. The effect of particle shape was found to be greater in loose specimens than in dense specimens. The effect of grain shape on critical state friction angle is also quantified.

Stress/strain data from mechanical testing of samples obtained from “as received” and fire damaged (400 °C and 500 °C) aluminum alloy 6061 plates is reported. Mechanical load information was obtained from load cells in the mechanical testing system while strain data was obtained from a digital imaging correlation system. For each plate condition (as received, 400 °C, 500 °C), four samples were machined along and across the rolling direction and subjected to four mechanical tests (tension, torsion, two combined tension/torsion tests) for a total of 24 unique combinations of condition, machining direction and loading path. Data from mechanical testing and digital imaging correlation systems was interpolated to generate stress/strain curves. Included data repository allows regeneration of stress/strain curves presented herein. Microscopy samples were obtained both from undeformed plates and deformed samples. Subsequent to polishing, EBSD was carried out and obtained microstructure and pole figures are reported.

Supplemental material, sj-pdf-1-jcm-10.1177_00219983211015721 for Thermo-mechanical characterization of discontinuous recycled/repurposed carbon fiber reinforced thermoplastic organosheet composites by Philip R Barnett, Stephen A Young, Vivek Chawla, Darren M Foster and Dayakar Penumadu in Journal of Composite Materials

Supplemental material, sj-pdf-2-jcm-10.1177_00219983211015721 for Thermo-mechanical characterization of discontinuous recycled/repurposed carbon fiber reinforced thermoplastic organosheet composites by Philip R Barnett, Stephen A Young, Vivek Chawla, Darren M Foster and Dayakar Penumadu in Journal of Composite Materials

Reactive thermoplastics are advantageous for wind turbine blades because they are recyclable at end of life, have reduced manufacturing costs, and enable thermal joining and shaping. However, there are challenges with manufacturing wind components from these new materials. This work outlines the development of manufacturing processes for a thick glass fiber–reinforced acrylic thermoplastic resin wind turbine blade spar cap, with consideration given to effects of the exothermic curing reaction on thick composite parts. Comparative elastic properties of these infusible thermoplastic materials with epoxy thermoset materials, as well as thermoplastic coupon components, are also included. Based on the results of this study it is concluded that the thermoplastic resin system is a viable candidate for the manufacturing of wind turbine blades using vacuum-assisted resin transfer molding. Significant gains in energy savings are realized avoiding heated molds, ability for recycling, and providing an opportunity for utilizing thermal welding.

Fire exposure causes significant mechanical property degradation of metallic materials. This paper investigates the influence of fire exposure on mechanical response of AA5083 through in situ neutron diffraction tensile tests and crystal plasticity finite element simulations. The Mechanical Threshold Stress (MTS) model is utilized, with a focus on the lattice strain response under tensile loading before and after exposure. A rigorous material parameter calibration procedure is proposed for this MTS model directly based on yield stress, plastic flow, hardening and rate dependency as a function of temperature, requiring only the macroscopic stress–strain curve. Material parameters of virgin material and fire-exposed material with full recrystallization are calibrated separately using this procedure. To initiate the investigation of mechanical degradation caused by fire exposure, a fire-exposed specimen with partial recrystallization is simulated by assigning material parameters and texture of recrystallized grains to selected grains in the virgin material according to the recrystallization fraction. Experimentally measured stress–strain curves and lattice strain evolution are employed to validate the simulations. For the first time, the local mechanical response of AA5083 is compared between in situ testing and finite element simulations, and the discrepancies of lattice strain evolution between virgin and fire-exposed material are discussed. Finally, the influence of fire-exposure on stress and lattice strain distribution is investigated to provide insight into mechanical property degradation.

The thermoplastic resin infiltration process in compression molded recycled/repurposed carbon fiber organosheet composites was studied experimentally to develop an understanding of optimal processing conditions for improved cycle time and infiltration quality. A custom permeameter employing highly viscous polydimethylsiloxane fluid to mimic a thermoplastic melt was built, and the measured permeability was compared to water and air measurements. The infiltrating fluid played a significant role in the measurement. A novel x-ray radiographic imaging system and measurement protocol were developed to evaluate the in-situ infiltration behavior during compression molding. Dual-scale permeability was observed as the highly viscous thermoplastic melt preferentially infiltrated interbundle spaces before filling intrabundle regions. Optical microscopy showed that infiltration pressure strongly impacts the microstructure of organosheets. Despite the decrease in infiltration time resulting from increased molding pressure, it was found that moderate pressures were preferable, yielding lower void content and a largely homogeneous fiber volume fraction.

The crashworthiness of discontinuous recycled carbon fiber composites was studied. Sinusoidal crush specimens were manufactured of acrylonitrile butadiene styrene, polyphenylene sulfide, and a common structural epoxy reinforced with recycled carbon fibers. Samples were tested at a range of strain rates and temperatures representative of automotive conditions. Crush debris size was quantified using sieving to correlate with energy absorption. The effect of manufacturing flaws such as embedded foreign objects, porosity, and ductile tearing was studied by comparing x-ray computed tomography images with crush test data gathered using digital image correlation. The results show great promise for discontinuous fiber organosheet composites as a novel material for automotive crash structures, exceeding the energy absorption capabilities of many continuous fiber thermosets.

Aluminum alloy AA6061 is of interest to the US Navy for ship structure applications due to its light weight, ease of manufacturing, corrosion resistance and strength. However, response to complex loading subsequent to fire damage presents a concern for practical applications. The purpose of this study is to evaluate the effect of fire damage on the microstructure and material response of AA6061 with applied tensile, torsional, and combined loading. Fire exposure was simulated in a controlled environment and testing under multi-axial loading conditions was carried out on virgin and fire damaged samples to evaluate mechanical response. Because of the non-circular sample cross-section, a three-dimensional digital image correlation technique was used to capture the evolution of local strains over the gage length of a deforming specimen subjected to tensile and/or torsional loading. Additionally, microstructure was investigated by electron backscatter diffraction at target cross-section locations subsequent to fire exposure and/or mechanical testing. Results indicate a 60–70% strength reduction with fire exposure. Fire exposed samples achieved higher maximum tensile load during combined loading compared to pure tensile loading. Microstructure was relieved by fire exposure while mechanical loading reveals strain-induced grain refinement. With sample geometry leading to stress concentrations, a deviation from yield values predicted by conventional yield criteria was observed; multi-axial stress-strain data can be of help in assessing the state of aluminum alloy structures after fire exposure.

Carbon fiber-reinforced vinyl ester composite facings are being considered by the US Navy for sandwich structures with either low-density polyvinyl chloride foam or balsa wood as the core materials manufactured using Vacuum-Assisted Resin Transfer Molding process. In this paper, experimental techniques are developed to evaluate the variation of surface strain spatially using three-dimensional Digital Image Correlation technique and internal damage evolution using radiation-based tomography. Both X-ray and neutron radiation was utilized to evaluate the microstructure of composite laminate facings in three dimensions at high resolution. Since naval structures are exposed to harsh sea environment, samples were soaked in simulated sea water at 40℃ for long duration, well beyond saturation stage of Fickian diffusion ascertained using weight gain measurements. Results for a series of mechanical tests on fiber dominated samples of [0/90]2S and matrix dominated samples of [±45]2S orientation are reported. Variable specimen sizes (12.5 mm wide by 100 mm long, 25 mm by 200 mm, and 25 mm by 300 mm, all with an average uniform thickness of 2.8 mm) for laboratory tests are utilized in order to evaluate the applicability of results for large ship structures. Different carbon fiber-reinforced vinyl ester failure mechanisms of matrix crack interactions, such as matrix dominated transverse tension, tension along fibers, and fiber delamination were observed. Digital Image Correlation technique was useful to track the existence of localized damage for both fiber and matrix dominated carbon fiber-reinforced vinyl ester laminates. High resolution X-ray and neutron tomography under in-situ mechanical loading were used to investigate interior microstructure evolution and damage at chosen stress levels. The new techniques presented in this paper can enable a comparison between interior specimen damage and surface damage (readily observable using Digital Image Correlation). Use of different modality of radiation (neutrons versus X-rays) was very useful to probe damage resulting from moisture diffused in the matrix resin and fiber interface/interphase and shows a lot of promise for studying the failure modes and damage evolution in polymeric composites and sandwich structures.

The evolution of spatially resolved internal strain/stress during the manufacturing of thermoplastic composites and subsequent relaxation from water intake are evaluated using an in-situ fiber optic sensor corresponding to a coated optical glass fiber with a nominal diameter of 160 μm. Unidirectional carbon fiber-polyamide 6 composites are produced using compression molding with an embedded fiber optic for strain measurement. The distributed fiber optic based strain sensor is placed in an arrangement to capture 0, 45, and 90° strains in the composite to resolve in-plane strain tensor. Strains are monitored in the direction of fiber optic sensor along its length at high resolution during the various stages of compression molding process. Results indicate considerable internal strains leading to residual stress at the end of processing step along the off-axis (45°) and transverse (90°) directions, and small strains in the carbon fiber pre-preg (0°) direction. At the end of compression molding process, an average of 7000 and 10,000 compressive micro-strains are obtained for residual state of strain in the off-axis and transverse direction. Since water/moisture infusion affects the mechanical properties of polyamide-6 matrix resin, these composite panels with embedded sensors targeted for marine applications are monitored in a water bath at 40 °C simulating accelerated testing conditions. Using the same fiber optic sensor based technique, the strain relaxation was observed during water uptake demonstrating in-situ strain monitoring during both manufacturing and subsequent composite implementation/application environment. The technique presented in this paper shows the potential of optimizing time-temperature-pressure protocols typically utilized in thermoplastic manufacturing, and continuous life-cycle monitoring of composite materials using a small diameter and inexpensive distributed fiber optic sensing.

In this paper, the degradation of mechanical properties of marine structural aluminum alloy AA5083 and onset of lattice plastic anisotropy subsequent to fire exposure is investigated. For virgin and fire-exposed samples, microstructural characterization is carried out for the first time and changes in lattice specific strain responses under step and continuous axial deformation are studied using novel bulk neutron diffraction. Peak fitting of raw data yields d-spacing values of reflections of interest and allows for lattice specific strain calculations. A reduction in yield stress from 260 MPa in the virgin material to 120 MPa in the fire-exposed sample is observed. Virgin material exhibits dynamic strain aging during plastic deformation; this is captured in neutron diffraction measurements. Larger peak broadening for virgin material indicates possible presence of Type II and III residual stresses due to intergranular stress or dislocation stress fields. Stress vs. lattice strain plots show large deviations from linearity post-yield for fire-exposed samples. This is due to strain redistribution among grains as well as grain reorientation. After fire exposure dynamic strain aging does not occur, but individual lattice planes reveal plastic anisotropy in their response to plastic deformation. Results from neutron diffraction, combined with electron backscatter diffraction characterization, provide insight into the yielding mechanisms of AA5083 and effects of fire exposure.

The hydromechanical response of partially saturated soils at macroscale is a manifestation of fundamental physics associated with pore scale. The Soil Water Characteristic Curve (SWCC) is an important state variable which affects mechanical as well as transport properties in a multiphase porous media. In present work, X-ray CT imaging and Pore Morphology Method (PMM) are leveraged to demonstrate robustness of a predictive approach in enhancing understanding of multiphase flow in sands from a pore scale perspective. The 3D microstructure of the Ottawa sand assembly is obtained from attenuation contrast-based X-ray Computed Tomography (CT) which serves as an input to PMM-based predictions. PMM relies on Young Laplace equation and mathematical morphology to simulate drainage and imbibition processes on an actual pore space. This approach is computationally efficient in comparison to computational fluid dynamics approach where highly nonlinear Navier Stokes equation is solved on a computational grid. In addition, the effect of X-ray CT resolution on SWCC predictions for drainage and imbibition is investigated. The effect of the surface roughness on wettability is demonstrated in numerical predictions by varying contact angle of the three-phase system. The spatial distribution of air and water corresponding to different capillary pressures is presented which can be helpful in developing improved multiscale modeling approaches in partially saturated sands.

Penetration depth is the most important parameter in terminal ballistics. Here only the case of projectiles penetrating granular medium is considered. Laboratory and field tests have shown that projectile characteristics such as mass, size, and nose shape, and target characteristics such as strength and density determine the depth of penetration. Analyses of full flight data recorded by onboard data acquisition system (G-Rec) are presented. These tests have revealed very high decelerations at impact with extensive particle fracture along the path of the projectile. Particle size distribution analysis of the sample collected from the projectile tip shows two to three orders of magnitude reduction in size. For similar impact velocities and target densities, Poncelet's coefficient does not vary with tip shape.

The penetration depth of a projectile is determined by the strength and deformation behavior of the granular material into which it impacts, which is affected by fracture of individual grains within the granular assembly. Interparticle forces, leading to contact stresses and ultimately fracture initiation, are influenced by particle morphology. A numerical method that incorporates both particle fracture and morphology can provide a more accurate model of projectile penetration. In this research, a numerical approach utilizing high resolution x-ray computed tomography (CT) to incorporate grain morphology and an explicit finite element code which includes damage mechanics for simulating grain fracture is used to analyze an assembly of Ottawa sand particles subjected to a one-dimensional confined compression loading, simulating the high stresses present at the tip of the projectile as it penetrates the ground. A small granular assembly of CT imaged Ottawa sand particles is analyzed with and without incorporating damage mechanics to investigate the initiation of particle fracture and its effect on the projectile's depth. This approach can then be used to create multi-scale models of granular assemblies under projectile loading considering the effect of individual particle shape and fracture on the penetration response through well calibrated numerical simulations.

The discrete nature of granular materials such as sands results in complex mechanical interactions such as non- affine deformations including slippage at grain contacts, force chain buckling and shear banding. Even until now, geomechanics community largely relies on triaxial testing as the basis for constitutive behavior at continuum scale. However, the continued evidence with the lack of suitable predictive models with reasonable number of parameters to capture phenomenological effects makes us believe that this problem is too complicated for any continuum-based approach. The pressing need is to incorporate mesoscale effects which are discrete and non-repeating in the numerical modeling, and hence FEM and X-ray CT imaging are explored concurrently. The conventional triaxial loading condition with actual morphology of particles, geometric contacts and arrangement of solid, void phases are modelled in this work. The comparison of results from simulations and experiments is demonstrated in addition to microstructural insights from strain localization.

Because of the recent advancements in hardware and reconstruction algorithms, multiphase flow modeling in porous media is experiencing a shift toward using advanced imaging techniques such ...

This chapter provides a summary of author’s findings from the research sponsored by the United States navy in the past decade associated with the durability aspect of the sandwich structures with thin face sheets made of carbon fiber vinyl ester composite facings and a thick core section of closed cell polymeric foam core material. Exposure to sea environment and coupled effects with temperature change to ship structures over extended period of time often leads to degradation of its mechanical properties. In this research, vinyl ester based carbon fiber composite facings manufactured using VARTM approach are evaluated for the fiber and resin dominated properties and corresponding degradation in static, fatigue, and fracture behavior. The mechanical response of carbon fiber vinyl ester composites immersed in simulated sea water and coupled degradation effects from simultaneous exposure to low temperature are reported. H100 PVC foam core degradation was evaluated under tension and torsion tests. Interfacial delamination fracture response for the sandwich structures due to combined effects of seawater and low temperature effects are also investigated including the weight gain and associated expansional hygroscopic strains. The effect of confined and one sided sea water exposure on the cyclic fatigue behavior yielded failures under much lower number of cycles of loading when fatigued under immersed conditions surrounded by sea water than in air for tension-tension fatigue. Even with the condition of one sided sample face exposed to sea water, a considerable reduction in the fatigue life, corresponding to approximately 50% was observed. A detailed study on the compression response of these naval composite sandwich structures is ongoing and is also included here.

Combined three-dimensional (3D) mapping of (micro-)structures with elemental and crystalline phase variations is of significant importance for the characterization of materials. Neutron wavelength selective imaging is a spectral imaging technique that exploits unique contrast differences e.g. for mapping dissimilar elemental, isotope, or phase compositions, and has the particular advantage of being applicable to sample volumes on the meso- and macroscale. While being mostly applied as radiography (2D) so far, we herein report that the extension to tomography allows for the display of the full spectral information for every voxel and in 3D. The development is supported by example data from a continuous as well as a pulsed neutron source. As a practical example, we collected 4D data sets (3D + spectral) of plastically deformed metastable stainless steel and herein demonstrate an improved quantification strategy for crystalline phase fractions. These exemplary results illustrate that localized phase transformations can be quantified even in complex geometries within centimeter-sized samples, and we will discuss the limits and future prospects of the technique that is not limited to crystalline materials.