THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

Soft materials are materials with a low shear modulus relative to their bulk modulus and where elastic restoring forces are mainly of entropic origin. A sparse population of strong bonds connects molecules together and prevents macroscopic flow. In this review we discuss the current state of the art on how these soft materials break and detach from solid surfaces. We focus on how stresses and strains are localized near the fracture plane and how elastic energy can flow from the bulk of the material to the crack tip. Adhesion of pressure-sensitive-adhesives, fracture of gels and rubbers are specifically addressed and the key concepts are pointed out. We define the important length scales in the problem and in particular the elasto-adhesive length Γ/E where Γ is the fracture energy and E is the elastic modulus, and how the ratio between sample size and Γ/E controls the fracture mechanisms. Theoretical concepts bridging solid mechanics and polymer physics are rationalized and illustrated by micromechanical experiments and mechanisms of fracture are described in detail. Open questions and emerging concepts are discussed at the end of the review.

/pdf/fracture-and-adhesion-of-soft-materials-a-review-4ydkznlufz.pdf

Fracture and adhesion of soft materials: a review.

Today, a large number of different steels are being processed by Additive Manufacturing (AM) methods. The different matrix microstructure components and phases (austenite, ferrite, martensite) and the various precipitation phases (intermetallic precipitates, carbides) lend a huge variability in microstructure and properties to this class of alloys. This is true for AM-produced steels just as it is for conventionally-produced steels. However, steels are subjected during AM processing to time-temperature profiles which are very different from the ones encountered in conventional process routes, and hence the resulting microstructures differ strongly as well. This includes a very fine and highly morphologically and crystallographically textured microstructure as a result of high solidification rates as well as non-equilibrium phases in the as-processed state. Such a microstructure, in turn, necessitates additional or adapted post-AM heat treatments and alloy design adjustments. In this review, we give an overview over the different kinds of steels in use in fusion-based AM processes and present their microstructures, their mechanical and corrosion properties, their heat treatments and their intended applications. This includes austenitic, duplex, martensitic and precipitation-hardening stainless steels, TRIP/TWIP steels, maraging and carbon-bearing tool steels and ODS steels. We identify areas with missing information in the literature and assess which properties of AM steels exceed those of conventionally-produced ones, or, conversely, which properties fall behind. We close our review with a short summary of iron-base alloys with functional properties and their application perspectives in Additive Manufacturing.

Steels in additive manufacturing: A review of their microstructure and properties

BACKGROUNDMetallic components are the cornerstone of modern industries such as aviation, aerospace, automobile manufacturing, and energy production. The stringent requirements for high-performance metallic components impede the optimization of materials selection and manufacturing. Laser-based additive manufacturing (AM) is a key strategic technology for technological innovation and industrial sustainability. As the number of applications increases, so do the scientific and technological challenges. Because laser AM has domain-by-domain (e.g., point-by-point, line-by-line, and layer-by-layer) localized forming characteristics, the requisite for printing process and performance control encompasses more than six orders of magnitude, from the microstructure (nanometer- to micrometer-scale) to macroscale structure and performance of components (millimeter- to meter-scale). The traditional route of laser-metal AM follows a typical “series mode” from design to build, resulting in a cumbersome trial-and-error methodology that creates challenges for obtaining high-performance goals.ADVANCESWe propose a holistic concept of material-structure-performance integrated additive manufacturing (MSPI-AM) to cope with the extensive challenges of AM. We define MSPI-AM as a one-step AM production of an integral metallic component by integrating multimaterial layout and innovative structures, with an aim to proactively achieve the designed high performance and multifunctionality. Driven by the performance or function to be realized, the MSPI-AM methodology enables the design of multiple materials, new structures, and corresponding printing processes in parallel and emphasizes their mutual compatibility, providing a systematic solution to the existing challenges for laser-metal AM. MSPI-AM is defined by two methodological ideas: “the right materials printed in the right positions” and “unique structures printed for unique functions.” The increasingly creative methods for engineering both micro- and macrostructures within single printed components have led to the use of AM to produce more complicated structures with multimaterials. It is now feasible to design and print multimaterial components with spatially varying microstructures and properties (e.g., nanocomposites, in situ composites, and gradient materials), further enabling the integration of functional structures with electronics within the volume of a laser-printed monolithic part. These complicated structures (e.g., integral topology optimization structures, biomimetic structures learned from nature, and multiscale hierarchical lattice or cellular structures) have led to breakthroughs in both mechanical performance and physical/chemical functionality. Proactive realization of high performance and multifunctionality requires cross-scale coordination mechanisms (i.e., from the nano/microscale to the macroscale).OUTLOOKOur MSPI-AM continues to develop into a practical methodology that contributes to the high performance and multifunctionality goals of AM. Many opportunities exist to enhance MSPI-AM. MSPI-AM relies on a more digitized material and structure development and printing, which could be accomplished by considering different paradigms for AM materials discovery with the Materials Genome Initiative, standardization of formats for digitizing materials and structures to accelerate data aggregation, and a systematic printability database to enhance autonomous decision-making of printers. MSPI-oriented AM becomes more intelligent in processes and production, with the integration of intelligent detection, sensing and monitoring, big-data statistics and analytics, machine learning, and digital twins. MSPI-AM further calls for more hybrid approaches to yield the final high-performance/multifunctional achievements, with more versatile materials selection and more comprehensive integration of virtual manufacturing and real production to navigate more complex printing. We hope that MSPI-AM can become a key strategy for the sustainable development of AM technologies. Download high-res image Open in new tab Download PowerpointMaterial-structure-performance integrated additive manufacturing (MSPI-AM).Versatile designed materials and innovative structures are simultaneously printed within an integral metallic component to yield high performance and multifunctionality, integrating in parallel the core elements of material, structure, process, and performance and a large number of related coupling elements and future potential elements to enhance the multifunctionality of printed components and the maturity and sustainability of laser AM technologies.

Material-structure-performance integrated laser-metal additive manufacturing.

Binder Jet printing is an additive manufacturing technique that dispenses liquid binding agent on powder to form a two-dimensional pattern on a layer. The layers are stacked to build a physical article. Binder Jetting (BJ) can be adapted to almost any powder with high production rates and the BJ process utilizes a broad range of technologies including printing tehniques, powder deposition, dynamic binder/powder interaction, and post-processing methods. A wide variety of materials including polymers, metals, and ceramics have been processed successfully with Binder Jet. However, developing printing and post-processing methods that maximize part performance is a remaining challenge. This article presents a broad review of technologies and approaches that have been applied in Binder Jet printing and points towards opportunities for future advancement.

Binder jetting: A review of process, materials, and methods

A critical review of powder-based additive manufacturing of ferrous alloys: Process parameters, microstructure and mechanical properties

In this study, the rate dependent energy dissipation process and the fracture toughness of physical gels were investigated using agarose as a sample material. Both the J-integral and Essential work of Fracture (EWF) methods were examined. To assess the quasistatic fracture toughness of gels, linear regression was performed on critical J (Jc) values at different loading rates resulting in a quasi-static Jc value of 6.5 J/m 2 . This is close to the quasi-static EWF value of 5.3 J/m 2 obtained by performing EWF tests at a quasi-static loading rate (crosshead speed of less than 2 mm/min). Nearly constant crack propagation rates at low loading rates, regardless of crack length, suggest viscoplastic chain pull-out is the fracture mechanism. At high loading rates failure was highly brittle, which is attributed to sufficient elastic energy accumulation to precipitate failure by chain scission. We conclude that in physical gels quasi-static fracture toughness can be evaluated by both the J-integral and EWF methods provided the effects of loading rate are investigated and accounted for. POLYM. ENG. SCI., 00:000–000, 2011. a 2011 Society of Plastics Engineers

http://mecheng1.uwaterloo.ca/~kwon/Publications_files/2011%20Fracture%20Toughness%20of%20Biogel.pdf

On the measurement of fracture toughness of soft biogel

Novel injectable hydrogels have been formed at 37 � C under physiological pH using a polymer-polymer cross- linking reaction. Three different formulations were tested. Af- ter 1-day cure time at body temperature, the elastic modulus of unswollen samples ranged between 3 and 5 kPa but after 11 additional days at 4 � C exceeded the target modulus of 10 kPa. Modulus data showed good agreement with theoretical crosslink density, enabling the prediction of stiffer/faster cur- ing gel formulations. Rubber elasticity theory provided a good fit to the experimental data up to 73% compressive true strain. Based on an analysis of modulus results, it was inferred that despite the presence of two aldehyde functional groups, only one mechanically significant crosslink can form per oxidized repeat unit on the alginate chain. V C 2011 Wiley

http://mecheng1.uwaterloo.ca/~kwon/Publications_files/2011%20Allan-Compressive%20stress-strain%20response%20of%20alginate%20chitosan%20hydrogels.pdf

Compressive stress-strain response of covalently crosslinked oxidized-alginate/N-succinyl-chitosan hydrogels

Understanding the mechanical properties of soft materials such as stress–strain behavior over a large deformation domain is essential for both mechanical and biological applications. Conventional measurement methods have limited access to these properties because of the difficulties in accurately measuring large deformations of soft materials. In this study, we optimized digital image correlation (DIC) method to measure the large-strain deformations by considering referencing scheme and frame rate. The optimized DIC was utilized to estimate strain in characterizing the stress–strain behavior of a polydimethylsiloxane (PDMS) elastomer as a model soft material. A series of comparative experimental studies and finite element analysis were performed; they indicated the advantages of optimized DIC over conventional methods such as robustness to slip, insensitivity to boundary conditions, and the ability to yield consistent and reliable results. These advantages enabled the optimized DIC to perform an in-depth analysis of the behavior of soft materials at large strain domain. An empirical constitutive equation to describe the large stress–strain behavior of PDMS was proposed and verified by finite element simulations that show excellent agreements with experimental results. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

The application of digital image techniques to determine the large stress–strain behaviors of soft materials

This study adopts the digital image correlation (DIC)
method to measure the mechanical properties under
tension in agarose gels. A second polynomial stress–
strain equation based on a pore model is proposed in
this work. It shows excellent agreement with experimental
data and was verified by finite element simulation.
Evaluation of the planer strain field by DIC allows
measurement of strain localization and Poisson’s ratio.
At high stresses, Poisson’s ratio is found to exceed the
standard assumption of 0.5 which is shown to be a
result of pore water leakage. Local failure strains are
found to be approximately twice those determined by
crosshead displacements. Viscous properties of agarose
gels are investigated by performing the tensile
tests at various loading rates. Increases in loading rate
do not cause much difference in the shape of stress–
strain curves, but result in increases in ultimate stress
and strain.

http://mecheng1.uwaterloo.ca/~kwon/Publications_files/2009%20DIC%20Agarose.pdf

Allan Rogalsky

Papers

A critical review of powder-based additive manufacturing of ferrous alloys: Process parameters, microstructure and mechanical properties

On the measurement of fracture toughness of soft biogel

Compressive stress-strain response of covalently crosslinked oxidized-alginate/N-succinyl-chitosan hydrogels

The application of digital image techniques to determine the large stress–strain behaviors of soft materials

Application of digital image correlation method to biogel