Modeling thermal and mechanical cancellation of residual stress from hybrid additive manufacturing by laser peening

Additive manufacturing (AM) of metals often results in parts with unfavorable mechanical properties. Laser peening (LP) is a high strain rate mechanical surface treatment that hammers a workpiece and induces favorable mechanical properties. Peening strain hardens a surface and imparts compressive residual stresses improving the mechanical properties of a material. This work investigates the role of LP on layer-by-layer processing of 3D printed metals using finite element analysis. The objective is to understand temporal and spatial residual stress development after thermal and mechanical cancellation caused by cyclically coupling printing and peening. Results indicate layer peening frequency is a critical process parameter affecting residual stress redistribution and highly interdependent on the heat generated by the printing process. Optimum hybrid process conditions were found to exists that favorably enhance mechanical properties. With this study, hybrid-AM has ushered in the next evolutionary step in AM and has the potential to profoundly change the way high value metal goods are manufactured

Mechanical Characterizations of 3D-printed PLLA/Steel Particle Composites

The objective of this study is to characterize the micromechanical properties of poly-L-lactic acid (PLLA) composites reinforced by grade 420 stainless steel (SS) particles with a specific focus on the interphase properties. The specimens were manufactured using 3D printing techniques due to its many benefits, including high accuracy, cost effectiveness and customized geometry. The adopted fused filament fabrication resulted in a thin interphase layer with an average thickness of 3 μm. The mechanical properties of each phase, as well as the interphase, were characterized by nanoindentation tests. The effect of matrix degradation, i.e., imperfect bonding, on the elastic modulus of the composite was further examined by a representative volume element (RVE) model. The results showed that the interphase layer provided a smooth transition of elastic modulus from steel particles to the polymeric matrix. A 10% volume fraction of steel particles could enhance the elastic modulus of PLLA polymer by 31%. In addition, steel particles took 37% to 59% of the applied load with respect to the particle volume fraction. We found that degradation of the interphase reduced the elastic modulus of the composite by 70% and 7% under tensile and compressive loads, respectively. The shear modulus of the composite with 10% particles decreased by 36%, i.e., lower than pure PLLA, when debonding occurred

Additive manufacturing of magnesium alloys

Magnesium alloys are a promising new class of degradable biomaterials that have a similar stiffness to bone, which minimizes the harmful effects of stress shielding. Use of biodegradable magnesium implants eliminates the need for a second surgery for repair or removal. There is a growing interest to capitalize on additive manufacturing\u27s unique design capabilities to advance the frontiers of medicine. However, magnesium alloys are difficult to 3D print due to the high chemical reactivity that poses a combustion risk. Furthermore, the low vaporization temperature of magnesium and common biocompatible alloying elements further increases the difficulty to print fully dense structures that balance strength and corrosion requirements. The purpose of this study is to survey current techniques to 3D print magnesium constructs and provide guidance on best additive practices for these alloys

Glocal integrity in 420 stainless steel by asynchronous laser processing

Cold working individual layers during additive manufacturing (AM) by mechanical surface treatments, such as peening, effectively “prints” an aggregate surface integrity that is referred to as a glocal (i.e., local with global implications) integrity. Printing a complex, pre-designed glocal integrity throughout the build volume is a feasible approach to improve functional performance while mitigating distortion. However, coupling peening with AM introduces new manufacturing challenges, namely thermal cancellation, whereby heat relaxes favorable residual stresses and work hardening when printing on a peened layer. Thus, this work investigates glocal integrity formation from cyclically coupling LENS® with laser peening on 420 stainless steel

Cellular Agriculture: An Outlook on Smart and Resilient Food Agriculture Manufacturing

Over the centuries, the application of grassland and cutting of livestock are the primary foundations for the production of food agriculture manufacturing. Growing human population, accelerated human activities globally, staggering food inequity, changing climate, precise nutrition for extended life expectancy, and more demand for protein food call for a new outlook to smartness in food agriculture manufacturing for delivering nutritious food. Cellular agriculture, 3D printing of food, vertical urban farming, and digital agriculture alongside traditional means are envisioned to transform food agriculture and manufacturing systems for acceptability, availability, accessibility, affordability, and resiliency for meeting demands of food in this century for communities across the US and the world. This technical note illustrates the thought leadership for cellular agriculture as a part of the new food agriculture manufacturing revolution

A Strategy to Optimize Recovery in Orthopedic Sports Injuries

An important goal for treatment of sports injuries is to have as short a recovery time as possible. The critical problem with current orthopedic implants is that they are designed to be permanent and have a high complication rate (15%) that often requires removal and replacement with a second surgery; and subsequently a second rehabilitation cycle. This study was designed to test the feasibility of having a device that could provide the needed mechanical properties, while promoting healing, for a specified amount of time and then degrade away, to shorten the recovery time. The specific strategy was to create a surface layer on a degradable metal alloy with a controllable degradation rate. Previous studies have shown the feasibility of using surface treatments to alter the surface integrity (i.e., topography, microhardness, and residual stress) leading to increased fatigue strength and a decreased degradation rate. This study was an extension of these previous studies to look at the changes in surface integrity and mechanical properties initially as well as the degradation over time for two surface treatments (shot peening and burnishing). Although the treatments improved initial properties and the burnishing treatment slowed degradation rate, the faster degradation of the base material in vitro (compared to previous studies) probably reduced the overall impact. Therefore although the study helped support the feasibility of this approach by showing the ability of the surface treatment to modify surface integrity, initial mechanical properties, and degradation rate; the degradation rate of the base material used needs to be slower and/or the surface treatment needs to create a bigger change in the degradation rate. Further it ultimately needs to be shown that the surface treatment can produce a material that will allow orthopedic devices to meet the required clinical design constraints in vivo

Ultra-fast charging in aluminum-ion batteries: electric double layers on active anode

With the rapid iteration of portable electronics and electric vehicles, developing high-capacity batteries with ultra-fast charging capability has become a holy grail. Here we report rechargeable aluminum-ion batteries capable of reaching a high specific capacity of 200 mAh g−1. When liquid metal is further used to lower the energy barrier from the anode, fastest charging rate of 104 C (duration of 0.35 s to reach a full capacity) and 500% more specific capacity under high-rate conditions are achieved. Phase boundaries from the active anode are believed to encourage a high-flux charge transfer through the electric double layers. As a result, cationic layers inside the electric double layers responded with a swift change in molecular conformation, but anionic layers adopted a polymer-like configuration to facilitate the change in composition

Increased ductility of Ti-6Al-4V by interlayer milling during directed energy deposition

Additive manufacturing (AM) often results in high strength but poor ductility in titanium alloys. Hybrid AM is a solution capable of improving both ductility and strength. In this study, hybrid AM of Ti-6Al-4V was achieved by coupling directed energy deposition with interlayer machining. The microstructure, residual stress, and microhardness were examined to explain how interlayer machining caused a 63% improvement in ductility while retaining an equivalent strength to as-printed samples. Interlayer machining introduced recurrent interruptions in printing that allowed for slow cooling-induced coarsening of acicular α laths at the machined interfaces. The coarse α laths on the selectively machined layers increased dislocation motion under tensile loads and improved bulk ductility. The results highlighted in this publication demonstrate the feasibility of hybrid AM to enhance the toughness of titanium alloys

Lithic technological responses to Late Pleistocene glacial cycling at Pinnacle Point Site 5-6, South Africa

There are multiple hypotheses for human responses to glacial cycling in the Late Pleistocene, including changes in population size, interconnectedness, and mobility. Lithic technological analysis informs us of human responses to environmental change because lithic assemblage characteristics are a reflection of raw material transport, reduction, and discard behaviors that depend on hunter-gatherer social and economic decisions. Pinnacle Point Site 5-6 (PP5-6), Western Cape, South Africa is an ideal locality for examining the influence of glacial cycling on early modern human behaviors because it preserves a long sequence spanning marine isotope stages (MIS) 5, 4, and 3 and is associated with robust records of paleoenvironmental change. The analysis presented here addresses the question, what, if any, lithic assemblage traits at PP5-6 represent changing behavioral responses to the MIS 5-4-3 interglacial-glacial cycle? It statistically evaluates changes in 93 traits with no a priori assumptions about which traits may significantly associate with MIS. In contrast to other studies that claim that there is little relationship between broad-scale patterns of climate change and lithic technology, we identified the following characteristics that are associated with MIS 4: increased use of quartz, increased evidence for outcrop sources of quartzite and silcrete, increased evidence for earlier stages of reduction in silcrete, evidence for increased flaking efficiency in all raw material types, and changes in tool types and function for silcrete. Based on these results, we suggest that foragers responded to MIS 4 glacial environmental conditions at PP5-6 with increased population or group sizes, 'place provisioning', longer and/or more intense site occupations, and decreased residential mobility. Several other traits, including silcrete frequency, do not exhibit an association with MIS. Backed pieces, once they appear in the PP5-6 record during MIS 4, persist through MIS 3. Changing paleoenvironments explain some, but not all temporal technological variability at PP5-6.Social Science and Humanities Research Council of Canada; NORAM; American-Scandinavian Foundation; Fundacao para a Ciencia e Tecnologia [SFRH/BPD/73598/2010]; IGERT [DGE 0801634]; Hyde Family Foundations; Institute of Human Origins; National Science Foundation [BCS-9912465, BCS-0130713, BCS-0524087, BCS-1138073]; John Templeton Foundation to the Institute of Human Origins at Arizona State Universit

Isotope evidence for the use of marine resources in the Eastern Iberian Mesolithic

There are relatively few coastal Mesolithic sites in the Iberian Mediterranean region, probably due to a number of factors including sea level changes and the disappearance of sites due to agriculture and urbanisation. However, recent excavations have uncovered inland sites that have marine faunal remains (i.e. molluscs and fish) and lithics from the coastal area, which both indicate interactions between the coast and the upland valleys. These inland sites are located at a distance of 30e50 km from today¿s coastline and are at altitudes higher than 1000 m. We report on additional information on the links between the coast and these inland sites through the use of dietary isotope analysis (carbon and nitrogen stable isotope analysis) of collagen extracted from human and faunal remains at the sites of Coves de Santa Maira, Penya del Comptador and Cingle del Mas Nou. The results indicate that Mesolithic diet in this region was largely based on C3 terrestrial resources, but there was measurable evidence of low-level consumption of marine resources at both coastal and inland sites