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Carbon fiber composites are now common in the aerospace industry because of their high specific stiffness and strength. They are ideal for decreasing the weight of structures, but it is well-known that they can suffer delamination and failure under relatively mild impact loads. In particular, under ballistic impact, carbon fiber composites underperform compared to other materials like S-2 glass, Kevlar®, or polyethylene composites. Hence, it is difficult to find in the literature a complete study aimed at obtaining a reliable computer model for ballistic impact on carbon fiber composites. This paper presents a thorough experimental campaign of both the material constituents and the composite, including loads in the different directions (longitudinal and transverse tension, shear, delamination, etc.) at low and high strain-rates, and ballistic tests. The study is performed on non-woven (2D) composite as well as a 3D woven composite with the same constituents. The material properties were determined using computations that reproduce the material tests. A mesoscale computer model was developed that is validated by comparing the results from the mechanical and ballistic test with the computations. It is shown that, using the properties obtained in the material test computations, the predictions for the ballistic tests are very good both for ballistic limits and deflections.

Recent accounts in Boston highlight tensions among individuals experiencing homelessness, individuals seeking treatment for substance use disorder, service providers, advocates, residents, and business owners in geographies colloquially referred to as “Mass and Cass.” The dynamic frictions of lived experience unfold in public spaces entangled in a field of social, political, economic, and spatial conditions. The Boston Architectural College, mission-driven to “provide excellence in design education emerging from practice and accessible to diverse communities,” sits less than a mile from these geographies. A curriculum in applied learning, where practicing and learning occurs concurrently, distinguishes the BAC’s educational approach from co-op or externship models. Its educational agenda recognizes the vital dialogue between academia and practice and locates teaching and learning directly within these conduits. This research-driven project focuses on the spatial, sociocultural geographies of Mass and Cass and examines the pedagogies of community participation and engagement in design education. The project addresses the nature of interdisciplinary teaching and learning in design settings through examining modes of critical thinking, listening, reflection, and translation as integral to civic spatial practices. Using the tools of spatial designers and conceptual frameworks from other disciplines, students attempt to understand the agents, actors, and forces at play in the conditions of Mass and Cass. Through critical inquiry into the sociocultural contexts that characterize the spatial narratives of Mass and Cass, students (and city agencies as collaborators) seek to identify moments when design or designers have, may have, or could have intervened in these contested territories.

Background Reducing inappropriate antibiotic prescriptions (Rxs) is a major quality improvement initiative in the United States. Tracking antibiotic prescribing trends is 1 method of assessing improvement in antibiotic prescribing. The purpose of this study was to assess longitudinal antibiotic prescribing practices among dental specialists. Methods This was a retrospective ecological longitudinal trend study. The authors calculated monthly systemic antibiotic Rx counts, and rates per 100,000 beneficiaries, from a pharmacy benefits manager in the United States from 2013 through 2015. The authors calculated average annual antibiotic Rx rates (AARs) for the 3-year study period. The authors used a quasi-Poisson regression model to analyze antibiotic Rx trends. The authors quantified seasonal trends, when present, via peak-to-trough ratios (PTTRs). Results Dental specialists prescribed 2.4 million antibiotics to the cohort of 38 million insurance beneficiaries during the 3-year study period (AAR = 2,086 Rxs per 100,000 beneficiaries). Oral and maxillofacial surgeons prescribed the most antibiotics (1,172,104 Rxs; AAR = 1,018 Rxs per 100,000 beneficiaries), followed by periodontists (527,038 Rxs; AAR = 457 Rxs per 100,000 beneficiaries), and endodontists (447,362 Rxs; AAR = 388 Rxs per 100,000 beneficiaries). Longitudinal antibiotic prescribing trends were stable among all dental specialties in the regression models (P > .05). The authors observed substantial seasonal variation in antibiotic Rxs in 2 specialties: pediatric dentistry (PTTR, 1.18; 95% confidence interval, 1.13 to 1.25) and orthodontics and dentofacial orthopedics (PTTR, 1.41; 95% confidence interval, 1.21 to 1.71), with the highest rates of antibiotic Rxs in the spring and winter. Conclusions Antibiotic prescribing practices for dental specialists remained stable. The authors observed seasonal trends in 2 specialties. Practical Implications Public health efforts are needed improve antibiotic prescribing among dental specialties.

The objective of this paper is to present an investigation of resistance welded thermoplastic joints using stainless steel wire mesh and polyethylene terephthalate (PET) with unidirectional E-glass fiber reinforcement. Five weld pressures and six heating element types were investigated to achieve high quality welds. Scanning electron microscope (SEM) images of welded heating element cross-sections were analyzed to provide a phenomenological description of the weld. Welded joints were also subjected to experimental lap shear evaluation and joint strengths were compared with values from the literature to assess the overall quality of welded joints. Characteristic B-basis strengths and corresponding SEM images are compared to lead to a recommended weld pressure of 345 kPa with a stainless steel wire mesh with 100 openings per inch.

Carbon fiber-reinforced composites typically do not perform as well as materials containing polymer and glass fibers in ballistic impact applications. This is due to the brittle nature of the carbon fibers, which cannot admit the larger deflections required for composite- and fabric-based armors to stop a projectile without breaking. That said, the high stiffness and strength and low density of carbon fiber composites makes them ideal for use in structural regions of vehicles, aircraft, and other assemblies that may be unintentionally subjected to high-rate impacts while in service. Thus, an understanding of the damage mechanisms active in carbon fiber composites during impact and how they differ from those that occur in polymer and glass fiber composites under similar conditions is of interest to anyone performing impact modeling of these materials. Tests of carbon fiber composites with two-dimensional non-crimp and three-dimensional woven architectures were devised in order to improve the understanding and modeling of these materials under impact conditions. Carbon fiber composite panels were subjected to ballistic impact to obtain both residual velocities of the projectiles and backface deflection measurements. Additionally, slow-rate mechanical tests of the composite were conducted to provide information about the material’s response under various stress states. Mesoscale models of the two- and three-dimensional composites were constructed. These models include individual elements for the carbon fiber tows, resin matrix, and interfaces between the two constituents. Results from the finite element computations were compared to both the ballistic impact and mechanical test data.

A three-dimensional progressive damage model has been developed to capture the onset and initial propagation of damage within a three-dimensional woven composite in a single-bolt, double-shear joint. Reinforced with a three-dimensional woven ply to ply interlock IM7 carbon fiber preform impregnated with toughened epoxy resin and manufactured using a resin transfer molding process, the composite represents a unique material currently used in select aerospace structures. The modeled joint is commonly found in many aerospace structures and, when combined with the progressive damage response of this three-dimensional woven composite, the material response can be reliably predicted with a three-dimensional non-linear finite element model. This model is constructed using an orthotropic material assumption far from the bearing area and a voxelized mesoscale model with an as-molded geometry representing matrix and impregnated tow phases. The well-established Hashin failure criteria and the Matzenmiller–Lubliner–Taylor damage model were implemented with the unique morphology of three-dimensional woven composites. The onset of damage and trends seen in the model were found to be in agreement with previous experimental findings.

[ILLUSTRATION OMITTED] [ILLUSTRATION OMITTED] Ed. Note: While working as part of the Student Action with Farmworkers program between his junior and senior year of college, Kyle was placed with Southern Migrant Legal Services, based in Nashville, Tennessee. Through his work, he met frequently with farmworkers contracted under the H-2A and H-2B guest worker programs across a five-state area, investigated farms historically known for labor violations, and researched legal precedent aiding and informing decisions in migrant farmworker cases. His stories are a collection of those interactions, both the lived experiences of his clientele and accounts from his firm's previous work. LUIS Luis lived in the storage facility where his company stored old sweet potatoes from last year's harvest, his bed among a large "bedroom" where about thirty other workers slept. The rank smell of rotting sweet potatoes lingered in the air, molding in their crates just a few feet away from where Luis slept at night. He told us everyone got used to the smell. But what he never got used to were occasional threats by snakes, scorpions, and spiders that lived in the crates and often came out at night. Luis hadn't been bitten or stung (yet), nor did he know anyone who had, but he was waiting for the day when someone would eventually get hurt. [ILLUSTRATION OMITTED] Basic amenities appeared scarce. Luis showed us the breakroom-turned-kitchen, which had two stoves--only one of which worked--and two refrigerators. But there was no real bathroom. Toward the back of the warehouse, the musky smell of rotting produce mingled with the pungent odor of raw sewage. The showering facilities where more than thirty workers lined up to bathe was nothing more than a spigot with a tarp fashioned around it. On the other side, raw sewage seeped up from the ground just inches away. Luis said it was difficult but there wasn't anywhere else to go that he knew of and patron Jack had tried to "do good by them." They would make do so long as they were provided with steady work and an honest paycheck. [ILLUSTRATION OMITTED] SYLVIA Sylvia loved the bright color of the tomatoes. There was something beautiful about plucking them from their vines each and every day. But that fruit often came at a high cost. Sylvia often spent an entire day picking tomatoes by the bushel, returning home with blisters, sores, and boils underneath her arms. The first couple months of work, she thought it was from repeatedly carrying a full basket to the truck. She was half-right. Hay una sintoma de laspesticidias. Her farm had been using very strong pesticides and herbicides to keep the tomatoes red. But she and other workers were never informed when the grower or crew leader sprayed the crops. There were no signs, just the hope that they would learn through word-of-mouth that it wasn't safe to go into the fields. Once, Sylvia was directly sprayed with chemicals while she was picking tomatoes under the hot sun. In such cases, Sylvia and others hoped to get to Wal-Mart in time for ointment that would reduce the swelling, but they paid for it out of their own pockets and knew better than to complain. "Those who complain often don't come back," she said. She worked with people whose skin began to peel because of prolonged exposure--so burned and so raw that it shined like a ruby-red, ripe tomato. [ILLUSTRATION OMITTED] MANUEL Manuel spent nearly two decades of his life picking apples in the southeast to provide an honest wage for his wife back in Mexico. Each year, he came to the States on an H-2A visa, working for the same grower. And each year, Manuel was loaded with others into an overcrowded bus with loose tools and no seat belts every morning at 6 am. By 7 am, he was in the fields, climbing the tall trees and picking its fruits for a piece-rate; bruised pieces were thrown out. Workers, including Manuel, commonly fell out of the trees that they toiled in. …

A comprehensive experimental evaluation of three-dimensional woven carbon composites arranged in various bolted bearing configurations is presented in this paper. Three unique three-dimensional woven fiber architectures were evaluated in single-bolt single-shear and double-shear configurations; two ply to ply angle interlock woven architectures were examined alongside an orthogonal woven architecture. All fiber architectures were woven with IM7 carbon in 12K and 24K tow sizes. To further enhance the understanding of these bolted connections, single-shear bolted joints were subjected to seven different loading orientations between the orthogonal warp and weft directions. Failure modes and fracture paths are analyzed and discussed for both single and double-shear experiments. Bearing strengths and stiffnesses for both single-shear and double-shear configurations were calculated and compared. Experimental results show that composites with three-dimensional woven fiber reinforcement exhibit exceptional strength when subjected to off-axis bearing loads despite the lack of off-axis reinforcement.

Two-dimensional (unidirectional) and 3-D woven carbon fiber reinforced plastic (CFRP) panels were produced by Albany Engineered Composites. Coupons were machined from the laminates for various mechanical tests in tension, torsion, and delamination. A batch of neat resin was also produced and the mechanical properties of the resin were determined. Some of the mechanical tests were performed at medium and high strain rates. The panels were tested under ballistic impact while recording the back face deflection with a stereo pair of high-speed cameras to perform digital image correlation. Additionally, an ultra-high-speed camera provided a better resolution of the initial (50 ms) pyramid that forms after impact. The mechanical tests were used to determine the material properties of the constituents as well as the strength of the interface between matrix and fibers. The properties were incorporated in material models in LS-DYNA to perform simulations of the mechanical tests as well as the ballistic experiments. The ballistic limits, residual velocities, and deflection histories served as a validation of the model and were predicted with good accuracy for two thicknesses of the two-dimensional composite and one of the 3-D composite.