scholarly journals Evolutionary optimization of material properties of a tropical seed

2011 ◽  
Vol 9 (66) ◽  
pp. 34-42 ◽  
Author(s):  
Peter W. Lucas ◽  
John T. Gaskins ◽  
Timothy K. Lowrey ◽  
Mark E. Harrison ◽  
Helen C. Morrogh-Bernard ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Material Properties ◽  
Turgor Pressure ◽  
Selection Pressures ◽  
Damage Mechanisms ◽  
Length Scales ◽  
Damage Resistance ◽  
Heterogeneous Microstructure ◽  
Upper Limit

Here, we show how the mechanical properties of a thick-shelled tropical seed are adapted to permit them to germinate while preventing their predation. The seed has evolved a complex heterogeneous microstructure resulting in hardness, stiffness and fracture toughness values that place the structure at the intersection of these competing selective constraints. Analyses of different damage mechanisms inflicted by beetles, squirrels and orangutans illustrate that cellular shapes and orientations ensure damage resistance to predation forces imposed across a broad range of length scales. This resistance is shown to be around the upper limit that allows cracking the shell via internal turgor pressure (i.e. germination). Thus, the seed appears to strike an exquisitely delicate adaptive balance between multiple selection pressures.

Effect of Moisture and Graded-Layer Mechanical Properties on Deformation and Interfacial Adhesion

2003 ◽  
Vol 778 ◽  
Author(s):  
Lorraine C. Wang ◽  
Reinhold H. Dauskardt
Keyword(s):  
Mechanical Properties ◽  
Layer Thickness ◽  
Material Properties ◽  
Interface Fracture ◽  
Material Structure ◽  
Second Phase ◽  
Length Scales ◽  
Adhesion Properties ◽  
Micron Size ◽  
Thermal And Electrical Properties

AbstractControlling material properties over nanometer length scales is crucial for current and emerging high-density microelectronic device packages. Miniaturization of devices is increasingly limited by the ability to “connect” to the device, and the required packaging structures must be fabricated where layer thickness and feature sizes approach micron size scales while achieving the required mechanical, thermal and electrical properties. Second phase additions such as sub-micron sized particles are often added to locally adjust the material properties of constituent layers in the complex package structure. This results in significant variation of mechanical properties over sub-micron length scales. Such manipulation of material structure and its effects on mechanical and interfacial fracture behavior are addressed using experimental and modeling studies. Underfill layers consisting of an epoxy matrix with dispersed silica beads are shown to exhibit variations of elastic and flow properties in excess of three-fold across the layer thickness. Mechanical properties are not only affected by the distribution of second-phase fillers, but also by the adhesion properties of the filler/matrix interface. Interfaces are susceptible to stress corrosion cracking associated with moisture which can lead to progressive debond growth at loads much lower than that required to exceed the critical interface fracture energies. Subcritical debonding is affected by temperature, humidity, and the bond chemistry of the interface. The effects of these variations are considered on the adhesive and subcritical debonding behavior of interfaces between model epoxy underfills and SiNx chip passivation. Implications for other constrained complex layered structures are considered.

Microstructural Design by Selective Grain Growth of β-Si3N4

1992 ◽  
Vol 287 ◽  
Author(s):  
Naoto Hirosaki ◽  
Yoshio Akimune ◽  
Mamoru Mitomo
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Material Properties ◽  
Weibull Modulus ◽  
Sintered Material ◽  
High Reliability ◽  
Uniform Size ◽  
Microstructural Design ◽  
Sintering Conditions

ABSTRACTRaw β-Si3N4 powder was gas-pressure sintered with Y2 O3-Nd2O3additives at > 1700ºC. Graingrowth behavior was investigated in relation to sintering conditions. Selective growth of large grains was accomplished by sintering the powder at high temperatures with small amounts of additives. As a result, in-situ composites were obtained from β-powder.The desired material properties have been attained by controlling the microstructural design using large grains. Materials with high reliability, having a Weibull modulus of about 50, were fabricated by maintaining a uniform size and distribution of elongated grains. Tough materials, having fracture toughness of, were developed by increasing the diameter of elongated grains. This method was applied to the sintering of refractory grade powder with the aim of lowering sintered material cost. Fairly good mechanical properties have been obtained even with impure powders.

Influence of heterogeneities with different length scale on the plasticity of Fe-base ultrafine eutectic alloys

2008 ◽  
Vol 23 (7) ◽  
pp. 2003-2008 ◽  
Author(s):  
Jin Man Park ◽  
Do Hyang Kim ◽  
Ki Buem Kim ◽  
Min Ha Lee ◽  
Won Tae Kim ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Room Temperature ◽  
Shear Bands ◽  
High Strength ◽  
Length Scale ◽  
Eutectic Alloys ◽  
Length Scales ◽  
Heterogeneous Microstructure ◽  
Evolution Of Microstructure ◽  
Co Alloys

The evolution of microstructure and its influence on the mechanical properties of high-strength ultrafine eutectic Fe–(Ti, Zr)–(B, Co) alloys has been studied. The addition of B or Co improves the room temperature compressive plasticity from 1% to ∼8.5% or ∼14%, respectively, due to the formation of a heterogeneous microstructure with distinctly different length scales, which can delay the propagation of shear bands and promotes the activation of multiple shear bands.

Effective Mechanical Properties of Carbon-Carbon Composites

2014 ◽  
Author(s):  
Aswathi Sudhir ◽  
Abhilash M. Nagaraja ◽  
Suhasini Gururaja
Keyword(s):  
Mechanical Properties ◽  
Effective Properties ◽  
Leading Edge ◽  
Carbon Composites ◽  
Length Scales ◽  
Heterogeneous Microstructure ◽  
Specific Strength ◽  
C Fibers ◽  
Exit Nozzle ◽  
Effective Mechanical Properties

In recent times, composite materials have gained mainstream acceptance as a structural material of choice due to their tailorability and improved thermal, specific strength/stiffness and durability performance [1–3]. For high temperature applications, which include exit nozzle for rockets, leading edge for missiles, nose cones, brake pads etc. Carbon-Carbon composites (C/C composite) are found suitable [4–6]. Mechanical property estimation of C/C composites is challenging due to their highly heterogeneous microstructure. The highly heterogeneous microstructure consists of woven C-fibers, C-matrix, irregularly shaped voids, cracks and other inclusions. Predicting the mechanical behavior of complex hierarchical materials like C/C composites is of interest which forms the motivation for the present work. A systematic study to predict the effective mechanical properties of C/C composite using numerical homogenization has been undertaken in this work. The Micro-Meso-Macro (MMM) principle of ensemble averages for estimating the effective properties of the composite has been adopted. The hierarchical length scales in C/C composites were identified as micro (single fiber with matrix), meso (fabric) and macro (laminate). Comparisons have been made with mechanical testing of C/C composites at different length scales.

Microstructural and fractographic characterization of B4C-Al cermets tested under dynamic and static loading

1989 ◽  
Vol 47 ◽  
pp. 562-563
Author(s):  
Gyeung Ho Kim ◽  
Mehmet Sarikaya ◽  
D. L. Milius ◽  
I. A. Aksay
Keyword(s):  
Thin Film ◽  
Mechanical Properties ◽  
Fracture Toughness ◽  
Static Loading ◽  
Carbon Deposition ◽  
Full Density ◽  
Unique Combination ◽  
Strong Component ◽  
Reaction Products

Cermets are designed to optimize the mechanical properties of ceramics (hard and strong component) and metals (ductile and tough component) into one system. However, the processing of such systems is a problem in obtaining fully dense composite without deleterious reaction products. In the lightweight (2.65 g/cc) B4C-Al cermet, many of the processing problems have been circumvented. It is now possible to process fully dense B4C-Al cermet with tailored microstructures and achieve unique combination of mechanical properties (fracture strength of over 600 MPa and fracture toughness of 12 MPa-m1/2). In this paper, microstructure and fractography of B4C-Al cermets, tested under dynamic and static loading conditions, are described.The cermet is prepared by infiltration of Al at 1150°C into partially sintered B4C compact under vacuum to full density. Fracture surface replicas were prepared by using cellulose acetate and thin-film carbon deposition. Samples were observed with a Philips 3000 at 100 kV.

Characterization of interfaces in CVD-coated nicalon fiber-reinforced SiC

1989 ◽  
Vol 47 ◽  
pp. 556-557
Author(s):  
K.L. More ◽  
R.A. Lowden
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Chemical Vapor ◽  
Chemical Vapor Infiltration ◽  
Frictional Stress ◽  
Fiber Reinforced ◽  
Pull Out ◽  
Carbon Coated ◽  
Fiber Matrix

The mechanical properties of fiber-reinforced composites are directly related to the nature of the fiber-matrix bond. Fracture toughness is improved when debonding, crack deflection, and fiber pull-out occur which in turn depend on a weak interfacial bond. The interfacial characteristics of fiber-reinforced ceramics can be altered by applying thin coatings to the fibers prior to composite fabrication. In a previous study, Lowden and co-workers coated Nicalon fibers (Nippon Carbon Company) with silicon and carbon prior to chemical vapor infiltration with SiC and determined the influence of interfacial frictional stress on fracture phenomena. They found that the silicon-coated Nicalon fiber-reinforced SiC had low flexure strengths and brittle fracture whereas the composites containing carbon coated fibers exhibited improved strength and fracture toughness. In this study, coatings of boron or BN were applied to Nicalon fibers via chemical vapor deposition (CVD) and the fibers were subsequently incorporated in a SiC matrix. The fiber-matrix interfaces were characterized using transmission and scanning electron microscopy (TEM and SEM). Mechanical properties were determined and compared to those obtained for uncoated Nicalon fiber-reinforced SiC.

Cytocompatibility and Material Properties of Poly-carbonate Urethane/Carbon Nanofiber Composites for Neural Applications

2003 ◽  
Vol 774 ◽  
Author(s):  
Janice L. McKenzie ◽  
Michael C. Waid ◽  
Riyi Shi ◽  
Thomas J. Webster
Keyword(s):  
Mechanical Properties ◽  
Carbon Nanofibers ◽  
Material Properties ◽  
Carbon Nanofiber ◽  
Scar Tissue ◽  
Tissue Response ◽  
Positive Interactions ◽  
Weight Percentage ◽  
Poly Carbonate

AbstractCarbon nanofibers possess excellent conductivity properties, which may be beneficial in the design of more effective neural prostheses, however, limited evidence on their cytocompatibility properties exists. The objective of the present in vitro study was to determine cytocompatibility and material properties of formulations containing carbon nanofibers to predict the gliotic scar tissue response. Poly-carbonate urethane was combined with carbon nanofibers in varying weight percentages to provide a supportive matrix with beneficial bulk electrical and mechanical properties. The substrates were tested for mechanical properties and conductivity. Astrocytes (glial scar tissue-forming cells) were seeded onto the substrates for adhesion. Results provided the first evidence that astrocytes preferentially adhered to the composite material that contained the lowest weight percentage of carbon nanofibers. Positive interactions with neurons, and, at the same time, limited astrocyte functions leading to decreased gliotic scar tissue formation are essential for increased neuronal implant efficacy.

CARLSON ALLOY C600 and C600 ESR

Alloy Digest ◽  
1994 ◽  
Vol 43 (11) ◽  
Keyword(s):  
Mechanical Properties ◽  
Solid Solution ◽  
Fracture Toughness ◽  
Cold Working ◽  
Elevated Temperatures ◽  
High Strength ◽  
Heat Treating ◽  
Solid Solution Alloy ◽  
Resistance To Oxidation ◽  
Good Workability

Abstract CARLSON ALLOYS C600 AND C600 ESR have excellent mechanical properties from sub-zero to elevated temperatures with excellent resistance to oxidation at high temperatures. It is a solid-solution alloy that can be hardened only by cold working. High strength at temperature is combined with good workability. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance as well as forming, heat treating, and machining. Filing Code: Ni-470. Producer or source: G.O. Carlson Inc.

SUPERSTON 40

Alloy Digest ◽  
1965 ◽  
Vol 14 (4) ◽  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Corrosion Resistance ◽  
Shear Strength ◽  
Physical Properties ◽  
Tensile Properties ◽  
Heat Treating ◽  
Aluminum Bronze

Abstract SUPERSTON 40 is an aluminum bronze containing 12% manganese and has good casting properties and excellent mechanical properties. It is recommended for any application where extreme corrosion resistance is required and where weldability is desired, such as propellers and marine equipment. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and compressive and shear strength as well as fracture toughness, creep, and fatigue. It also includes information on corrosion resistance as well as casting, forming, heat treating, and machining. Filing Code: Cu-150. Producer or source: H. Kramer & Company.

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