Dynamic Indentation Hardness and Rate Sensitivity in Metals

1999 ◽  
Vol 121 (3) ◽  
pp. 257-263 ◽  
Author(s):  
G. Subhash ◽  
B. J. Koeppel ◽  
A. Chandra
Keyword(s):  
Vickers Hardness ◽  
High Speed ◽  
Rate Sensitivity ◽  
Indentation Hardness ◽  
Dynamic Indentation ◽  
Rate Dependent ◽  
Static Hardness ◽  
Rate Processes ◽  
Engineering Materials ◽  
Static Conditions

An experimental technique for determining the dynamic indentation hardness of materials is described. Unlike the traditional static hardness measurements, the dynamic hardness measurements can capture the inherent rate dependent material response that is germane to high strain rate processes such as high speed machining and impact. The dynamic Vickers hardness (DHV) of several commonly used engineering materials is found to be greater than the static Vickers hardness (HV). The relationship between the hardness and yield stress under static conditions, i.e., HV =3σy, is also found to be valid under dynamic conditions. It is suggested that this simpler technique can be used to assess the rate sensitive nature of engineering materials at moderate strain rates in the range of around 2000/s.

Effect of Rate Sensitivity on Necking Behavior of a Laminated Tube Under Dynamic Loading

2013 ◽  
Vol 81 (5) ◽  
Author(s):  
Y. Shi ◽  
P. D. Wu ◽  
D. J. Lloyd ◽  
D. Y. Li
Keyword(s):  
Dynamic Loading ◽  
High Speed ◽  
Volume Fraction ◽  
Numerical Study ◽  
Rate Sensitivity ◽  
Element Model ◽  
Localized Necking ◽  
Rate Dependent ◽  
Positive Rate ◽  
Laminated Materials

An elastic-viscoplastic based finite element model has been developed to study the necking behavior of tube expansion for rate independent materials, rate dependent monolithic materials, and laminated materials during dynamic loading. A numerical study shows that for rate independent materials, the dynamic loading will not delay diffused necking but localized necking; for rate dependent materials, high strain rate sensitivity can significantly delay the onset of localized necking for both monolithic and laminated sheets and affect the multiple-neck formation in high-speed dynamic loading. The model also shows that a higher volume fraction of a clad layer with positive rate sensitivity material in a laminated sheet improves the sheet ductility.

Indentation Rate-Dependent Creep Behavior of Sn-Ag-Cu Pb-Free Ball Grid Array (BGA) Solder Joint

2005 ◽  
Vol 502 ◽  
pp. 399-404
Author(s):  
Feng Jiang Wang ◽  
Xin Ma ◽  
Yiyu Qian
Keyword(s):  
Solder Joint ◽  
Hold Time ◽  
Rate Sensitivity ◽  
Ball Grid Array ◽  
Indentation Load ◽  
Indentation Hardness ◽  
Rate Dependent ◽  
Indentation Tests ◽  
Free Solder ◽  
Micro Indentation

Berkovich micro-indentation tests with different loading rates have been performed on the ball grid array solder joint with a Pb-free solder, Sn-4.0Ag-0.5Cu alloy. The resulting indentation load-depth curves are rate dependent and have varying creep penetration depths during the same hold time. Creep indentation hardness and rate sensitivity have been defined from the concept of “work of indentation”. The rate sensitivity of BGA solder joint is 0.0574.

Similarity Relationships in Creep Contacts and Applications in Nanoindentation Tests

2009 ◽  
Vol 1224 ◽  
Author(s):  
Jinhaeng Lee ◽  
Cong Zhou ◽  
Caijun Su ◽  
Yanfei Gao ◽  
George Pharr
Keyword(s):  
Strain Rate ◽  
Effective Strain ◽  
Rate Sensitivity ◽  
Amorphous Selenium ◽  
Coarse Grained ◽  
Indentation Hardness ◽  
Effective Strain Rate ◽  
Rate Dependent ◽  
Constitutive Parameters ◽  
The Relationship

AbstractThe study of indentation responses of rate-dependent (viscoplastic or creeping) solids has generally focused on the relationship between indentation hardness and an effective strain rate, which can be defined from a similarity transformation of the governing equations. The strain rate sensitivity exponent can be determined from the slope of a log-log plot of the hardness versus effective strain rate, while determining other constitutive parameters requires a knowledge of the relationship between contact size, shape, and indentation depth. In this work, finite element simulations have shown that the effects of non-axisymmetric contact and crystallography are generally negligible. Theoretical predictions agree well with real nanoindentation measurements on amorphous selenium when tested above glass transition temperature, but deviate quite significantly for experiments on high-purity indium, coarse-grained aluminum, and nanocrystalline nickel. Such a discrepancy is likely to result from the transient creep behavior.

Platelet and Shear Rate Promote Tumor Cell Adhesion to Human Endothelial Extracellular Matrix - Absence of a Role for Platelet Cyclooxygenase

1989 ◽  
Vol 61 (03) ◽  
pp. 485-489 ◽  
Author(s):  
Eva Bastida ◽  
Lourdes Almirall ◽  
Antonio Ordinas
Keyword(s):  
Cell Adhesion ◽  
Shear Rate ◽  
Tumor Cell ◽  
Umbilical Vein ◽  
Blood Platelets ◽  
Flow Conditions ◽  
Tumor Cell Adhesion ◽  
Rate Dependent ◽  
Static Conditions

SummaryBlood platelets are thought to be involved in certain aspects of malignant dissemination. To study the role of platelets in tumor cell adherence to vascular endothelium we performed studies under static and flow conditions, measuring tumor cell adhesion in the absence or presence of platelets. We used highly metastatic human adenocarcinoma cells of the lung, cultured human umbilical vein endothelial cells (ECs) and extracellular matrices (ECM) prepared from confluent EC monolayers. Our results indicated that under static conditions platelets do not significantly increase tumor cell adhesion to either intact ECs or to exposed ECM. Conversely, the studies performed under flow conditions using the flat chamber perfusion system indicated that the presence of 2 × 105 pl/μl in the perfusate significantly increased the number of tumor cells adhered to ECM, and that this effect was shear rate dependent. The maximal values of tumor cell adhesion were obtained, in presence of platelets, at a shear rate of 1,300 sec-1. Furthermore, our results with ASA-treated platelets suggest that the role of platelets in enhancing tumor cell adhesion to ECM is independent of the activation of the platelet cyclooxygenase pathway.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Numerical Analysis of Plane-Strain Tension Test for Rate-Dependent Solids

1992 ◽  
Vol 59 (3) ◽  
pp. 485-490 ◽  
Author(s):  
P. Tugˇcu
Keyword(s):  
Numerical Analysis ◽  
Strain Rate ◽  
Plane Strain ◽  
Rate Sensitivity ◽  
Tension Test ◽  
Engineering Strain ◽  
Plane Strain Tension ◽  
Rate Dependent ◽  
Strain And Strain Rate ◽  
Strain Rate Hardening

The plane-strain tension test is analyzed numerically for a material with strain and strain-rate hardening characteristics. The effect of the prescribed rate of straining is investigated for an additive logarithmic description of the material strain-rate sensitivity. The dependency to the imposed strain rate so introduced is shown to have a significant effect on several features of the load-elongation curve such as the attainment of the load maximum, the onset of localization, and the overall engineering strain.

STUDY ON THE FORMATION MECHANISM OF TANGJIASHAN LANDSLIDE TRIGGERED BY WENCHUAN EARTHQUAKE USING DDA SIMULATION

2011 ◽  
Vol 08 (02) ◽  
pp. 229-245 ◽  
Author(s):  
AIQING WU ◽  
QIGUI YANG ◽  
GUISHENG MA ◽  
BO LU ◽  
XIAOJUN LI
Keyword(s):  
Wenchuan Earthquake ◽  
High Speed ◽  
Total Duration ◽  
Sliding Surface ◽  
Geological Investigation ◽  
Earthquake Load ◽  
Nonlinear Features ◽  
Displacement Based ◽  
Static Conditions ◽  
In The Beginning

Wenchuan earthquake, Ms 8.0 in magnitude and occurred on May 12, 2008 in Sichuan Province, China, triggered a lot of landslides, rock collapses, debris flow, etc. The Tangjiashan landslide, with its total volume 20.37 million m3, was the biggest and the most notable one for its effects. Based on the field geological investigation and the typical acceleration records of the main shock obtained in the period of the earthquake, numerical simulation of the whole sliding process of Tangjiashan landslide has been carried out by DDA method. It is shown that the Tangjiashan landslide was a high-speed landslide, behaved with nonlinear features in the whole sliding process. The total duration of the landslide was about 30 s while nearly all of their slipping displacements were carried out in the beginning 25 s, with the maximum sliding velocity about 30 m/s, and the average 15–17 m/s in the beginning 25 s. The crash of rock blocks induced a much higher stresses near the middle and lower parts of the landslide, with the maximum value of 6–7 MPa. The dynamic earthquake load caused an incessant deformation of the landslide, resulting in the reduction of mechanical parameters, especially the shear strength on the sliding surface and the ratio of friction coefficient on sliding surface in kinematical and static conditions are no more than 0.35. DDA simulation considering the displacement-based parameter reduction has been developed in the original DDA code, and its results primarily reflect the evolvement process of a landslide under strong seismic loads.

scholarly journals Oxidation Resistance of a Si–TiSi2–MoSi2–TiB2–CaSi2 Coating on a Cf/C–SiC Substrate in High-Speed High-Enthalpy Air Plasma Flows

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2637
Author(s):  
Alexey Astapov ◽  
Lev Rabinskiy ◽  
Olga Tushavina
Keyword(s):  
Oxide Film ◽  
Oxidation Resistance ◽  
High Speed ◽  
Protective Action ◽  
Structural Phase ◽  
Silicon Monoxide ◽  
Air Plasma ◽  
Plasma Flows ◽  
Main Layer ◽  
Static Conditions

The results of a study on the development and testing of a heat-resistant coating in a Si–TiSi2–MoSi2–TiB2–CaSi2 system to protect Cf/C–SiC composites from oxidation and erosional entrainment in high-speed flows are presented here. The coating was formed using firing fusion technology on the powder composition. Oxidation resistance tests were carried out under static conditions in air at 1650 °C and under conditions of interaction with high-speed air plasma flows, with Mach numbers M = 5.5–6.0 and enthalpy 40–50 MJ/kg. The effectiveness of the protective action of the coating was confirmed at surface temperatures of Tw = 1810–1820 °C for at least 920–930 s, at Tw = 1850–1860 °C for not less than 510–520 s, at Tw = 1900–1920 °C for not less than 280–290 s, and at Tw = 1940–1960 °C for not less than 100–110 s. The values of the rate of loss of the coating mass and the rate constant of heterogeneous recombination of atoms and ions of air plasma on its surface were estimated. The performance of the coating was ensured by the structural-phase state of its main layer, and the formation and evolution on its surface during operation of a passivating heterogeneous oxide film. This film, in turn, is composed of borosilicate glass with titanium and calcium liquation inhomogeneities, reinforcing TiO2 microneedles and in situ Si2ON2 fibers. It was shown that at Tw≥ 1850–1860 °C, the generation of volatile silicon monoxide was observed at the “oxide layer–coating” interface, followed by the effects of boiling and breakdown degradation of the oxide film, which significantly reduced the lifespan of the protective action of the coating.

The Effect of Strain-Rate Upon the Tensile Deformation of Materials

1975 ◽  
Vol 97 (2) ◽  
pp. 151-155 ◽  
Author(s):  
R. G. Davies ◽  
C. L. Magee
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
High Speed ◽  
Tensile Deformation ◽  
Rate Sensitivity ◽  
Al Alloys ◽  
Reinforced Plastics ◽  
Strain Behavior ◽  
Static Testing ◽  
Dynamic Factors

The tensile strength of seventeen engineering materials including steels, Al alloys, and fiber-reinforced plastics, has been determined at strain-rates from 10−3 to 103 sec−1. Variable effects on the stress-strain behavior were found in the different materials with the Al alloys showing minimal strain-rate sensitivity and the plastics highest. All results exhibit a logarithmic dependence of flow stress on strain-rate and thus the dynamic factors (ratio of dynamic to low rate or quasi-static strengths) are as dependent upon changes in quasi-static testing speed (∼1 in./min (0.42 mm/s) as they are to changes at high speed (50,000 in./min or 50 mph (22.35 m/s). No significant influence of strain-rate on elongation or reduction in area has been found for any of the materials. Steels, which comprise the majority of the presently investigated materials, exhibit a higher rate sensitivity for yielding than for higher strain deformation. It is shown that the flow stress results for these steels leads to an internally consistent scheme when (1) strength level and (2) strengthening mechanisms are properly accounted for.

scholarly journals Strain rate and thermal softening effects in shear testing of AA7075-T6 sheet

2018 ◽  
Vol 183 ◽  
pp. 02037 ◽  
Author(s):  
Taamjeed Rahmaan ◽  
Ping Zhou ◽  
Cliff Butcher ◽  
Michael J. Worswick
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Rate Sensitivity ◽  
Thermal Conditions ◽  
Shear Loading ◽  
Image Correlation ◽  
High Rate ◽  
Strain Rates ◽  
Shear Testing ◽  
Plane Shear

Shear tests were performed at strain rates ranging from quasi-static (0.01 s-1) to 500 s-1 for AA7075-T6 sheet metal alloy at room temperature. A miniature sized shear specimen was used in this work to perform high strain rate shear testing. Digital image correlation (DIC) techniques were employed to measure the strains in the experiments. At maximum in-plane shear strains greater than 20%, the AA7075-T6 alloy demonstrated a reduced work hardening rate at elevated strain rates. At lower strains, the AA7075-T6 alloy showed mild positive rate sensitivity. The strain to localization (using the Zener-Holloman criterion), measured using the DIC technique, decreased with strain rate in shear loading. The strain at complete failure, however, exhibited an increase at the highest strain rate (500 s-1). The current work also focused on characterization of the thermal conditions occurring during high rate loading in shear with in situ high speed thermal imaging. Experimental results from the highest strain rate (500 s-1) tests showed a notable increase in temperature within the specimen gauge region as a result of the conversion of plastic deformation energy into heat.

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