Hard materials, particularly tooling compositions based on WC/Co structures, are predominantly designed for applications that take advantage of their extremely good properties in compression. There ...is a standard test method for obtaining compression properties (strength and ductility), ISO 4506:1979, but it is rather expensive to use, needing high capacity testing machines and, in some cases, quite complex testpieces to avoid problems with premature failure from parasitic tensile stresses at the platen/testpiece interface. Consequently, for the most part, the compressive properties of hardmetals are estimated through measurements of hardness; using techniques such as Rockwell (ISO 3738: parts 1–1982 and 2–1988) or Vickers (ISO 3878:1983). This paper discusses the correlation of hardness values with compression data and reviews the testing background, advantages and disadvantages of the test methods, together with comments on the underlying science and comparative studies by complementary researchers. The adoption of stiff compressive testing rigs at NPL for the measurement of almost 40 grades of hardmetals with a comprehensive spread of microstructures is used to comment on good testing practice.
•Issues associated with deformation metrologies.•Assessment of RT compression tests for WC-Co hardmetals.•Property mapping for WC-Co hardmetals.•Comparisons of data from different souces.
In order to reduce the testing errors in Rockwell hardness of metal specimens and improve the accuracy of hardness testing, several methods had been tried out and examined based on GB/T 230 and other ...relevant inspection specifications, firstly, correct the hardness of testing pieces directly by using the hardness reference blocks to calibrate the hardness tester; secondly, correct the hardness of testing pieces by linear calculation of the errors in different hardness values to calibrate the hardness tester; for a great deal of testing pieces, check the hardness twice and the second time in a reverse order. The result shows that the applied methods are effective to further improve the accuracy of Rockwell hardness testing.
Replicating bacterial chromosomes continuously demix from each other and segregate within a compact volume inside the cell called the nucleoid. Although many proteins involved in this process have ...been identified, the nature of the global forces that shape and segregate the chromosomes has remained unclear because of limited knowledge of the micromechanical properties of the chromosome. In this work, we demonstrate experimentally the fundamentally soft nature of the bacterial chromosome and the entropic forces that can compact it in a crowded intracellular environment. We developed a unique “micropiston” and measured the force-compression behavior of single Escherichia coli chromosomes in confinement. Our data show that forces on the order of 100 pN and free energies on the order of 10 ⁵ k BT are sufficient to compress the chromosome to its in vivo size. For comparison, the pressure required to hold the chromosome at this size is a thousand-fold smaller than the surrounding turgor pressure inside the cell. Furthermore, by manipulation of molecular crowding conditions (entropic forces), we were able to observe in real time fast (approximately 10 s), abrupt, reversible, and repeatable compaction–decompaction cycles of individual chromosomes in confinement. In contrast, we observed much slower dissociation kinetics of a histone-like protein HU from the whole chromosome during its in vivo to in vitro transition. These results for the first time provide quantitative, experimental support for a physical model in which the bacterial chromosome behaves as a loaded entropic spring in vivo.
Objectives: In selecting a denture base material, different polymerization techniques might be considered to avoid adverse effects of brushing on the microhardness of the acrylic resin. The purpose ...of this study was to evaluate the brushing effect on Vickers microhardness of acrylic denture base resins polymerized by different techniques.
Material and Methods: One hundred disk-shaped specimens (15 mm in diameter and 2 mm thick) were fabricated from each acrylic resin (Integra and FuturaJet). Five different polymerization techniques were tested (n=20): conventional water-bath polymerization, short autoclave polymerization (60°C for 30 minutes, then 130°C for 10 minutes), long autoclave polymerization (60°C for 30 minutes, then 130°C for 20 minutes), injection-molding polymerization and auto-polymerization. Half of the specimens were subjected to simulated brushing in an automatic brushing machine using 54 000 brush strokes for each specimen. All specimens were then submitted to Vickers hardness test with a 300-g load for 15 s. Mann Whitney U test and Kruskal-Wallis test followed by Dunn’s post-hoc test were used for results analysis, which were statistically significant at p < 0.05.
Results: A statistically significant difference was observed between the control and brushing groups in all polymerization techniques (p < 0.05). Autopolymerized acrylic resin group showed significantly lower microhardness values than water bath, short and long autoclave polymerized resins in control and brushing groups (p < 0.05).
Conclusions: Autopolymerization technique might has some disadvantages on avoid adverse effects of brushing on the microhardness, therefore tehniques of polymerization should be considered as microhardness of acrylic denture base resins.
Scanning probe microscopies (SPM) and cantilever-based sensors generally use low-frequency mechanical devices of microscale dimensions or larger. Almost universally, off-chip methods are used to ...sense displacement in these devices, but this approach is not suitable for nanoscale devices. Nanoscale mechanical sensors offer a greatly enhanced performance that is unattainable with microscale devices. Here we describe the fabrication and operation of self-sensing nanocantilevers with fundamental mechanical resonances up to very high frequencies (VHF). These devices use integrated electronic displacement transducers based on piezoresistive thin metal films, permitting straightforward and optimal nanodevice readout. This non-optical transduction enables applications requiring previously inaccessible sensitivity and bandwidth, such as fast SPM and VHF force sensing. Detection of 127 MHz cantilever vibrations is demonstrated with a thermomechanical-noise-limited displacement sensitivity of 39 fm Hz(-1/2). Our smallest devices, with dimensions approaching the mean free path at atmospheric pressure, maintain high resonance quality factors in ambient conditions. This enables chemisorption measurements in air at room temperature, with unprecedented mass resolution less than 1 attogram (10(-18) g).
Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip ...experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.
In this work, pristine carbon aerogels (CAs) were used as Pt-free counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) by varying the molar ratio of their precursors. Pristine mesoporous ...CAs with controlled resorcinol (R)/formaldehyde (F) and resorcinol (R)/sodium carbonate (C) molar ratios were successfully prepared. The as-prepared CAs were synthesized
via
a polymeric sol-gel reaction and were labeled as CA-O, CA-Q, CA-F, CA-C, and CA-G. The DSSCs using the as-prepared CA-C CE gave the best power conversion efficiency (PCE,
η
), 9.08 ± 0.01%, among all the CA CEs. The CA-C CE is further applied to an indoor T5 light source system with an impressive
η
value of 20.1 ± 0.60% at 2.18 mW cm
−2
(T5 lamp with 7000 lux). Moreover, the hardness of CA-C CE is 3.01 GPa (Brinell hardness test), which is comparable to that of the FTO/glass substrate. As a result, the CA-C CE shows great potential to replace traditional CEs based on the Pt/FTO/glass in DSSCs.
The best carbon aerogel CE gives an
η
of 9.08% at 100 mW cm
−2
and 20.1% at 2.18 mW cm
−2
.
Ti6Al4V alloy samples prepared by selective laser melting (SLM) were nitrided at a high temperature of 900 °C and then coated with amorphous carbon nitride (CN) or DLC-doped Ti (TiC:H) thin films ...using a closed field unbalanced magnetron sputtering (CFUMS) system. The microstructures, mechanical properties and coating adhesion strengths of the various specimens were evaluated by X-ray diffraction, nanoindentation tests and Rockwell hardness tests, respectively. The tribological properties of the samples were examined in 0.89 wt% NaCl solution by means of reciprocating sliding wear tests performed against 316L, Si3N4 and Ti6Al4V balls under a load of 10 N for 1440 s. In addition, the corrosion properties were evaluated by potentiodynamic polarization tests. Finally, cytotoxicity tests were performed using mouse leukemic monocyte macrophage cells (Raw 264.7) for culture periods of 1, 3 and 5 days, respectively. Overall, the Ti6Al4V sample processed using a duplex nitriding and DLC coating treatment exhibited a good coating adhesion, the highest wear resistance, the best corrosion resistance and excellent biocompatibility.
•Nitriding and coating technologies are used to treat Ti6Al4V samples produced by selective laser melting method.•Duplex surface treatment significantly improves the mechanical, tribological, corrosive properties and biocompatibility, in order to meet the requirement.•Surface-treated Ti6Al4V is a highly promising candidate for load-bearing artificial implants.
The mechanical properties of enamel and dentin were studied using test specimens having the same shape and dimensions because these properties might vary with the experimental conditions and specimen ...shapes and dimensions. Healthy human teeth were used as specimens for mechanical tests. The stress (MPa), strain (%), and elastic modulus (E, MPa) of the specimens were obtained from compression tests. The maximum stresses of the enamel, dentin, and enamel–dentin specimens were 62.2 ± 23.8, 193.7 ± 30.6, and 126.1 ± 54.6 MPa, respectively. The maximum strains of the enamel, dentin, and enamel–dentin specimens were 4.5 ± 0.8%, 11.9 ± 0.1%, and 8.7 ± 2.7%, respectively. The elastic moduli of the enamel, dentin, and enamel–dentin specimens were 1338.2 ± 307.9, 1653.7 ± 277.9, and 1628.6 ± 482.7 MPa, respectively. The measured hardness value of enamel specimens (HV = 274.8 ± 18.1) was around 4.2 times higher than that of dentin specimens (HV = 65.6 ± 3.9). Judging from the measured values of the stress and strain of enamel specimens, enamel tended to fracture earlier than dentin; therefore, it was considered more brittle than dentin. However, judging from the measured hardness values, enamel was considered harder than dentin. Therefore, enamel has higher wear resistance, making it suitable for grinding and crushing foods, and dentin has higher force resistance, making it suitable for absorbing bite forces. The different mechanical roles of enamel and dentin may arise from their different compositions and internal structures, as revealed through scanning electron micrographs of enamel and dentin.
Depositing Ni-based films on Cu pads has been accepted as an effective strategy to address the reliability challenges due to the development of plastic ball grid array (PBGA) in electronic packaging ...technology. Modification mechanisms of Co on Ni film and Sn-37 wt%Pb/Ni/Cu solder joints were researched from experimental and theoretical methods in this work. Experimental results suggested the additional minor Co element (12.46 at.%) led to the formation of Ni–Co solid solution. After reflowing, Ni3Sn4 intermetallic compound (IMC) was formed within Sn–37Pb/Ni/Cu system while (Ni,Co)3Sn4 IMC was produced at solder/Ni–Co interface. Nano-indentation tests indicated that the doping of Co enhanced the mechanical properties of Ni film and Ni3Sn4 IMC. Our single-lap shear tests demonstrated that the shear strength of Sn–37Pb/Ni/Cu reflowing joints increased from 24.68 to 29.72 MPa with the addition of Co. Moreover, theoretical investigations based on first-principles calculations were carried out to uncover the Co strengthening mechanism. The calculated results noted that the improved stability of coating/IMC interface and mechanical properties of coating and IMC phases were the main reasons for the enhanced shear strength of Sn–37Pb/Ni–Co/Cu solder joints.
•We successfully prepared eletrodeposited Ni or Ni–Co film on Cu substrate.•The additional Co improved the shear strength of Sn–37Pb/Ni/Cu from 24.68 to 29.72 MPa.•The improvement of Co due to the enhanced strength of coating/IMC interface, Ni–Co film and (Ni,Co)3Sn4 IMC.
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