Methodology for Evaluating Weight Savings from Basic Material Properties

Physical cues, such as extracellular matrix stiffness, direct cell differentiation and support tissue-specific function. Perturbation of these cues underlies diverse pathologies, including osteoarthritis, cardiovascular disease and cancer. However, the molecular mechanisms that establish tissue-specific material properties and link them to healthy tissue function are unknown. We show that Runx2, a key lineage-specific transcription factor, regulates the material properties of bone matrix through the same transforming growth factor-β (TGFβ)-responsive pathway that controls osteoblast differentiation. Deregulated TGFβ or Runx2 function compromises the distinctly hard cochlear bone matrix and causes hearing loss, as seen in human cleidocranial dysplasia. In Runx2+/⁻ mice, inhibition of TGFβ signalling rescues both the material properties of the defective matrix, and hearing. This study elucidates the unknown cause of hearing loss in cleidocranial dysplasia, and demonstrates that a molecular pathway controlling cell differentiation also defines material properties of extracellular matrix. Furthermore, our results suggest that the careful regulation of these properties is essential for healthy tissue function.

Annealing is a commonly used fabrication technology of graphene-assembled materials, which serves as an efficient method to control material properties. In graphene-assembled materials, the multilayer folded configuration of graphene has been widely observed due to the two dimensional characteristic of graphene. However, the manipulation on the mechanical properties of graphene-assembled materials by annealing has not been fully understood yet, especially considering the effect of folded microstructures. In this paper, we focus on the effect of annealing temperature on the mechanical properties of multilayer folded graphene. The dependences of elastic modulus, tensile strength, ultimate strain and fracture toughness on the annealing temperature have been systematically studied by molecular dynamics simulations. Moreover, the mechanisms behind the manipulations by annealing temperature have been revealed combining the structural evolutions obtained from the simulations. Our results indicate that the multilayer folded graphene after annealing under higher temperature exhibits significant reinforcement on its elastic modulus and tensile strength, while its ultimate strain drops instead. The fracture toughness is enhanced only within a certain range of annealing temperature. The controllable mechanical properties are attributed to the formation of interlayer covalent bonds between carbon atoms belonging to adjacent layers during the annealing processing. With the annealing temperature increases, more interlayer crosslinks are observed from simulations, which greatly strengthens the interlayer interaction. For the cases with lower annealing temperature, the folded graphene can be unfolded easily then finally flattened under tensile stretch, and the structural failure originates from the interlayer slippage in the folded area. However, for the cases with higher annealing temperature, the unfolding deformation is prevented since the folded graphene is blocked by much denser interlayer crosslinks, and the origins of structural failure transforms to the intralayer fracture in graphene plane. Considering the intralayer covalent bond interaction is far more powerful than the interlayer van der Waals interaction, the higher annealing temperature will bring higher elastic modulus and tensile strength due to the change on the structural failure mode, but it will sacrifice the ductility at the same time due to the blocked unfolding process of folded area. It is confirmed in our study that the annealing is an effective approach for the synthetic modulation on the stiffness, strength, ductility and toughness of multilayer folded graphene.

Fracture behavior of 3D-printed thermoplastics—A dilemma of fracture toughness versus fracture energy

Chapter 25 - Laminated composite structures

As part of a continuing program to provide data to aid in the prediction of materials' behavior, tests were conducted to compare the effects of various corrosive environments on the fatigue crack propagation rates of several 7075-T76511 and 7050-T76511 extruded shapes. The ASTM E399 compact specimen was used, and test variables included stress intensity (A/0 and grain direction, with the stress range ratio and test frequency being held constant (R = 0.1,6 Hz). Other tests included static mechanical properties, constant amplitude fatigue, fracture toughness, stress corrosion resistance, and exfoliation corrosion resistance. The tests showed that the fatigue strengths of the two alloys were similar except that, in the low-load, high-cycle range, the 7050-T76511 provided a slight advantage. Fracture toughness (KIc) ranged from 17 to 50 ksiVm. and was found to vary significantly with specimen orientation. Fatigue crack growth rates (DA/DN) in the various test environment increased in the following order: dry air, moist air, sump water, salt water. The effect of test environment was more prominent than specimen orientation at K however, higher-toughness material did tolerate more stable crack growth before failure and, therefore, would provide improved tolerance to crack damage, i.e., longer life, in a service environment.

The elements of railway turnouts made from rail sections of R260 high carbon steel must have a high resistance to abrasive and contact fatigue wear, as well as a good resistance to cracking under service loads. These mechanical properties largely determine the suitability of steel for use as railway track components. In this study, two groups of specimens were subjected to tests of mechanical properties and metallurgical analyses. The first group included material obtained from the hot-rolled block section, the rolling end temperature being Tkw = 950°C, while the second group was material after the rolling process with the subsequent 20-minute isothermal annealing at a temperature of 480°C. The microstructure of tested materials (Rm, Rp0.2, A5, Z, HB) was characterized, and their basic mechanical properties and fracture toughness in the KIc plane strain condition were determined. Also the effect of temperature, ranging from-80°C to 100°C, on the KCU impact toughness of R260 steel was established. Based on the SEM observation using the Hitachi S-3400N scanning microscope, it was found that pearlitic structure with a varied distance between cementite plates, equal to 0.29 μm and 0.09 μm, respectively, appears in the hot-rolled R260 steel and in the steel subjected to additional isothermal annealing treatment. The impact of pearlite morphology on the cracking characteristics and basic mechanical properties of materials was analyzed. It was found that at room temperature, the higher fracture toughness (KIc = 66.4 MPa·m1/2) is shown by the steel after isothermal annealing at 480°C, in which less distance between the plates of cementite has been observed in the perlite. The fracture toughness of R260 steel after hot rolling at 950°C was KIc = 48.3 MPa·m1/2. As in the case of fracture toughness, the impact strength of R260 steel after isothermal annealing was significantly greater than the impact strength of steel only after hot rolling. The determined cracking characteristics of R260 steel make it possible to determine the effect of heat treatment on the formation of microstructure and material properties, which determine the service life of rail sections.

The influence of parameters contributing to rubber stiffness, including, crosslink density, hardness, and modulus, on the crack growth and abrasion resistance of carbon black‐filled purified natural rubber (PNR) vulcanizates as well as a whole natural rubber (WNR) vulcanizate counterpart or a control were elucidated. In addition, the tensile properties of PNR and WNR were also determined. PNR containing the same curative level as that of the control had lower stiffness and exhibited superior crack growth resistance. The results revealed that the improved crack growth resistance of PNR, compared to the control, was due to its lower crosslink density, hardness, and modulus. In addition, the tensile strength and abrasion resistance of PNR vulcanizates were not as sensitive as the crack growth resistance to the changes of their stiffness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1793–1796, 2003

Recent advances in the area of Metal Matrix Composites (MMC's) have brought these materials to a maturity stage where the technology is ready for transition to large-volume production and commercialization. The new materials seem to allow the fabrication of higher quality parts at less than 50 percent of the weight as compared to steel, especially when they are selectively reinforced with carbon, silicon carbide, or aluminum oxide fibers. Most of the developments in the MMC materials have been spurred, mainly by applications that require high structural performance at elevated temperatures, the heavy vehicle industry could also benefit from this emerging technology. Increasing requirements of weight savings and extended durability are the main drivers for potential insertion of MMC technology into the heavy vehicle market. Critical elements of a typical tractor-trailer combination, such as highly loaded sections of the structure, engine components, brakes, suspensions, joints and bearings could be improved through judicious use of MMC materials. Such an outcome would promote the DOE's programmatic objectives of increasing the fuel efficiency of heavy vehicles and reducing their life cycle costs and pollution levels. However, significant technical and economical barriers are likely to hinder or even prevent broad applications of MMC materials in heavy vehicles. The tradeoffs between such expected benefits (lower weights and longer durability) and penalties (higher costs, brittle behavior, and difficult to machine) must be thoroughly investigated both from the performance and cost viewpoints, before the transfer of MMC technology to heavy vehicle systems can be properly assessed and implemented. MMC materials are considered to form one element of the comprehensive, multi-faceted strategy pursued by the High Strength/Weight Reduction (HS/WR) Materials program of the U.S. Department of Energy (DOE) for structural weight savings and quality enhancements in heavy vehicles. The research work planed for the first year of this project (June 1, 2003 through May 30, 2004) focused on a theoretical investigation of weight benefits and structural performance tradeoffs associated with the design, fabrication, and joining of MMC components for heavy-duty vehicles. This early research work conducted at West Virginia University yielded the development of integrated material-structural models that predicted marginal benefits and significant barriers to MMC applications in heavy trailers. The results also indicated that potential applications of MMC materials in heavy vehicles are limited to components identified as critical for either loadings or weight savings. Therefore, the scope of the project was expanded in the following year (June 1, 2004 through May 30, 2005) focused on expanding the lightweight material-structural design concepts for heavy vehicles from the component to the system level. Thus, the following objectives were set: (1) Devise and evaluate lightweight structural configurations for heavy vehicles. (2) Study the feasibility of using Metal Matrix Composites (MMC) for critical structural components and joints in heavy vehicles. (3) Develop analysis tools, methods, and validated test data for comparative assessments of innovative design and joining concepts. (4) Develop analytical models and software for durability predictions of typical heavy vehicle components made of particulate MMC or fiber-reinforced composites. This report summarizes the results of the research work conducted during the past two years in this projects.

The objective of this effort is to predict ceramic matrix composites (CMC) interlaminar Mode II Crack Growth Resistance (CGR), and the design of ASTM test specimen. Currently, there are a number of test standards and American Society for Testing and Materials (ASTM) for CMC’s at both ambient and elevated temperatures; however, there are no standardized test methods for determination of interlaminar shear (Mode II) fracture toughness in CMC’s. Although research work exists on interlaminar Mode II fracture toughness of CMC’s, the test methods applied showed definite drawbacks and limitations. Delamination Crack Growth (CGR) tests of CMC Mode II may exhibit zig-zag pattern, wavy cracks, fiber bridging, and premature specimen failure under bending load. The experimental parameters that may contribute to the difficulty can be summarized as specimen width and thickness, interface coating thickness, mixed mode failure evolution, and interlaminar defects. Modes II crack growth resistances, GII, were analytically and numerically determined at ambient temperature using end notched flexure (ENF) and the end-loaded split (ELS). Finite Element (FE) based. Multi-scale progressive failure analysis (MS-PFA) a combined Micro-mechanical damage and fracture mechanics Virtual Crack Closure Technique (VCCT) algorithms. Modeling of melt-infiltrated SiC/SiC CMC of ENF specimen (Laminate: with initial crack length was accomplished using a MS-PFA and VCCT approach. Test data were compared with MS-PFA prediction: a) Force vs. Crack Opening Displacement; and b) Mode II crack tip energy release rate vs. crack extension length for both edge and center line due to formation of Micro Crack Density Contribution, Crack Tip Stiffness Reduction; and c) zig-zag crack growth behavior (adhesive/cohesive). Next the ASTM Standard Proposed linear SGR equation was developed based on interpretation compliance technique from both MS-PFA Analysis and Test.

In this study, the variations of the basic mechanical performance properties (microhardness (Hv), elastic modulus, hardness shear modulus, brittleness index, yield strength, elastic hardness coefficient, fracture toughness, ductility, flexibility and durability) of new Bi2.1-xBaxSr2.0Ca1.1Cu2.0Oy superconducting materials produced by doping different amounts (ranging from 0.0≤x≤0.1) of barium ions into the crystal matrix of Bi2.1Sr2.0Ca1.1Cu2.0Oy (Bi-2212) superconducting material were investigated in detail by microindentation Vickers hardness (Hv) tests in the applied load range 0.245N-2.940 N. In addition, the change of resistance to crack propagation, durable tetragonal phase, mechanical efficiency and mechanical characteristics of the Bi-2212 ceramic system with Ba/Bi partial substitution in the crystal structure was determined. According to experimental and theoretical findings, the overall mechanical performance of the Bi-2212 superconducting crystal structure increased significantly up to the Ba/Bi replacement level of x=0.01, while a systematic reduction was observed after this substitution ratio. In this context, it was found that barium doped at optimum level restricts the dislocation movements in the crystal structure and causes lattice strain change around the dislocation. Furthermore, the optimum presence of barium in the crystal lattice let to the formation of new slip systems within the structure, new bond formations between atoms, reduction of stress regions on the surface and rise at strength and fracture toughness. Besides, the optimum substitution level resulted in improved material crystal quality and intergranular bonding. When the mechanical characteristic behavior was examined, it was found that all materials presented the typical indentation size effect (ISE) characteristic and there was a significant improvement in the ISE characteristic in the case of optimum replacement ratio.

Both environmental embrittlement and crack tip visco-plastic stress relaxation play a significant role in determining the dwell fatigue crack growth (DFCG) resistance of nickel-based disk superalloys.In the current study performed on the Low Solvus High Refractory (LSHR) disk alloy, the influence of these two mechanisms were separated so that the effects of each could be quantified and modeled.Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments.Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth.For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior.The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for viscoplastic behavior.Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates.It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses.It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior.To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress intensity parameter, Kmax, was developed by incorporating into the formulation the remaining stress level concept as measured by simple stress relaxation tests.The newly proposed parameter, Ksrf, did an excellent job in correlating the dwell crack growth rates for the four heat treatments which were shown to have similar intrinsic environmental cyclic fatigue crack growth resistance.

Crack growth resistance in dual-phase steel was studied. The dual phase steel microstructure was modified through heat treatments to increase the martensite volume fraction from 10% to 40%. The as-received and heat-treated samples were evaluated using a uniaxial tensile test, fatigue crack growth test, and fracture toughness test. Extended Finite Element Method (XFEM) was used to simulate the crack growth in compact tension test specimens. The results showed that an increase in martensite volume fraction is an effective way to increase the fracture resistance under different load conditions, quasistatics and dynamic, increasing the fracture toughness, tensile strength and fatigue resistance of the heat-treated material. Presence of a highest content of martensite results in formation of an important number of secondary cracks during the fatigue crack growth, which slow down the crack propagation. Moreover, martensite generates a crack closure over the crack tip, making the propagation difficult due to the irregularities caused by the crack growth on the martensite. Finally, the computational load-displacement curves are in good agreement with the experimental data.

This study aimed to determine the effect of variations in material properties of the intervertebral disc on dynamic response of the human lumbar spine to vertical vibration using a finite element model of the lumbar L1-S1 motion segment. The present material sensitivity study was conducted by varying elastic moduli for annulus ground substance (AGS), annulus fibers (AF), and nucleus pulposus (NP) in the disc. Transient dynamic analysis was performed initially on the model with basic material property under a sinusoidal vertical vibration load. Subsequently, the same analysis was done for each of the three disc components corresponding to high and low material property cases. The computed results were plotted as a function of time and compared. The AGS property displayed a larger impact on vertebral axial displacement and von Mises stress in AGS, and the AF property displayed a larger impact on disc bulge. In contrast, the NP property had little effect on all the response parameters. Additionally, the intradiscal pressure was found to be not sensitive to any of the disc properties. These findings may be helpful in adoption of appropriate material parameters for the intervertebral disc in finite element model of the lumbar spine used for vibration analysis. Graphical abstract Material property sensitivity analysis on vibration characteristics of the human lumbar spine.

Fracture toughness and fatigue crack growth resistance of precipitate-free and precipitation hardened NiTiHf shape memory alloys

Aiming at the mechanical and structural characteristics of the contact zone composite rock, the shear tests and numerical studies were carried out. The effects of the differences in mechanical properties of different materials and the normal stress on shear properties of contact zone composite samples were analyzed from a macro-meso level. The results show that the composite samples have high shear strength, and the interface of different materials has strong adhesion. The differences in mechanical properties of materials weakens the shear strength and increase the shear brittleness of the sample, while normal stress will inhibit these effect. Under low/high normal stress, the sample show two failure modes, at the meso-damage level: elastic-shearing-frictional sliding and elastic-extrusion wear. This is mainly controlled by the contact and friction state of the material after damage. The secondary failure of undulating structure under normal-shear stress is the nature of extrusion wear, which is positively correlated to the normal stress and the degree of difference in mechanical properties of different materials. The increase of the mechanical difference of the sample will enhance the shear brittleness under lower normal stress and the shear interaction under higher normal stress.