SiCp／ZTM材料高温静态及循环疲劳寿命的预测

对组份为ＳｉＣｐ／ＺＴＭ材料进行室温９２０℃下的力学性能测定，并采用Ｋｎｏｏｐ压痕梁三点弯曲测试方法进行了９２０℃下静态疲劳，动态疲劳实验，获得了Ｐａｒｉｓ指数和三参数Ｗｅｉｂｕｌｌ模数，在此基础上建立了应力－时间－断裂几率关系，对其进行寿命预测。     

陶瓷材料Vickers 硬度的压痕尺寸效应

本工作对几种陶瓷材料Ｖｉｃｋｅｒｓ硬度的压痕尺寸效应进行了研究,证实了经典的Ｍｅｙｅｒ方程可以很好地描述实验数据,但这一方程无助于对压痕尺寸效应物理本质的认识,基于能量平衡考虑或这发展起来的试样比例阻力（ＰＳＲ）模型得到的另一个半经验公式,只能对在一个较窄的荷载范围内测得的实验数据作出准确描述,本文提出了一个 半经验公式用以描述所观察到的压痕尺寸效应,并就这一新公式的物理意义进行了简要的讨论。     

静载多点压痕对氮化硅陶瓷强度的影响

本文在对XJM－1型磨片机进行改装的基础上研究了静载多点压痕对氮化硅陶瓷强度的影响。实验发现：与原始强度相比，静载多点压痕后的氮化硅强度有所降低；强度与多点压痕荷载之间的关系曲线出现一极大值。分析后表明：表面残余应力与裂纹尺寸是影响陶瓷材料强度的两个主要因素，它们的变化将对陶瓷材料强度产生直接影响。     

涂料与涂膜物性的最新评价方法(Ⅲ)

２．７．５巴克霍尔兹硬度法巴克霍尔兹硬度法也叫压痕试验（ＩｎｄｅｎｔａｔｉｏｎＴｅｓｔ）。系采用有一定尺寸和质量的巴克霍尔兹压痕硬度试验器,在规定的条件下施加于涂层上,其形成的压痕长度表现了涂层对压头压入的抵抗能力,结果以抗压痕性来表示。式中：Ｈ─抗压痕性Ｌ─压痕长度,ｍｍ从实际测量来看,白色和彩色漆膜的压痕长度易于判断,且压痕硬度在硬膜比较明显,并与漆膜厚度有关。压痕图形见图１６。此法符合ＩＳＯ２８１５、ＤＩＮ５３１５３。ＧＢ９２７５等标准。美国ＡＳＴＭ　Ｄ１４７４－９２则推荐使用Ｋｎｏｏｐ压…     

氮化硅陶瓷冲蚀磨损特性研究

对Ｓｉ３Ｎ４陶瓷进行冲蚀磨损和断裂韧性测定，对磨损表面和断口进行扫描电镜观察。结果表明：压痕断裂是热压烧结Ｓｉ３Ｎ４产生冲蚀的控制机制；Ｓｉ３Ｎ４的冲蚀率ＥＶ与断裂韧性ＫＩＣ有强烈的依赖关系，随ＫＩＣ的增高冲蚀抗力迅速增高，即ＥＶ∝ＫＩＣ＾ｎ，ｎ值变动于－７．０￣－４．４之间；依磨粒硬度ＨＥ和Ｓｉ３Ｎ４硬度Ｈ的比值和ＫＩＣ的大小可以评价Ｓｉ３Ｎ４陶瓷的抗冲蚀特性；热压烧结Ｓｉ３Ｎ４有很高的抗冲蚀性     

利用冲击球压法评价混凝土表面的硬化特征

为了研究硬化阶段混凝土表面性能受环境影响而变化的特性,利用冲击球压技术研究了非常规养护制度下(室外、水中及5%Na2SO4溶液)混凝土的冲击荷载与压痕尺寸的关系、动态硬度及恢复系数,对混凝土材料的冲击压痕形貌进行了分析.结果表明:(1)水中养护的混凝土动态硬度和恢复系数较大,随着养护时间的延续增长最快;自然环境中放置的混凝土动态硬度和恢复系数最小,硬化初期这两项性能有一定的增长,但是在硬化中后期发生下降;(2)5%Na2SO4溶液中养护的混凝土硬化初期动态硬度和恢复系数较大,随养护时间的延续动态硬度缓慢增长,而恢复系数明显下降;整个试验证明,利用冲击球压技术评价混凝土的硬化程度是可行的.     

Si3N4陶瓷材料高温力学性能和断裂行为定量化实验研究

陶瓷构件常常服役于高温极端环境，易发生脆性断裂破坏。然而，关于陶瓷材料定量化的高温微观断裂研究报道较少。本文基于硅钼棒加热技术开展了Si₃N₄陶瓷材料高温维氏压痕实验，测试了惰性环境下，材料从室温至1200℃间的维氏硬度和断裂韧性，定量化表征了典型温度下的裂纹偏转和穿沿晶行为。研究表明：Si₃N₄陶瓷材料的维氏硬度、断裂韧性和杨氏模量在高温下有一定的降低，实验温度下的沿晶裂纹比例远大于穿晶裂纹比例，而裂纹偏转角分布随温度的变化不大。     

几类典型结构陶瓷材料的冲蚀磨损行为研究

研究了几类典型结构陶瓷材料，如Ａｌ２Ｏ３，ＳｉＣ，Ｓｉ３Ｎ４陶瓷，Ａｌ２Ｏ３－ＺｒＯ２系相变增韧陶瓷（ＺＴＡ，ＴＺＰ）和ＳｉＣｗ／Ｓｉ３Ｎ４系晶须补强陶瓷（ＷＲＳＮ）有９０ｍ／ｓ下的冲蚀磨损性能，以及其与材料性能（硬度，断裂韧性）和冲蚀条件（粒子硬度，冲击角度）之间的关系，分析了冲蚀磨损机制。陶瓷材料的低角冲蚀磨损机制主要包括：研磨状损伤，犁沟状微切削损伤和晶粒剥落。低角冲蚀磨损率随材料硬度的增加     

氮化铝的室温热导率

本文导出了氮化铝室温热导率的一般表达式，对提高氮化铝陶瓷材料室温热导率的途径作了讨论。     

含氧化物的部分二氧化锆陶瓷的抗裂性及其它性能

本文探讨了用氧化钇稳定的二化锆陶瓷的强度、弹性、硬度及抗裂性。在该陶瓷中加入氧化铁增强组份。在低温及高温下详细研究了该材料的某些特性，查明其三点法抗折强度为为９７７ＭＰａ，利用带切口条状试样测定的应力强度临界系数ＫＩＣ达１６．７ＭＰａ．ｍ＾１／２。探讨抗裂性时，利用一些常用方法，并对这睦方法作了分析。例如，查明了２条状度样进行抗折试验时于５００Ｎ的荷重下实施压头压痕，常温下ＫＩＣ值为９．５ＭＰａｍ     

Recommendations for Determining the Hardness of Armor Ceramics

It is empirically known that an armor ceramic should be as hard or harder than the projectile it intends to defeat. Quasi-static indentation testing is one of the most widely utilized techniques for determining the hardness of armor ceramics. Hardness measurements can also be used to generate other property values that may be relevant to ballistic performance (fracture toughness, elastic properties, and even the yield strength). While the indentation methodologies are simple and straight forward, the resultant hardness values for ceramic materials can be influenced by the indenter geometry, indentation load, loading rate, specimen surface finish, and microstructure. This presentation will summarize the results of a study to determine the hardness of a variety of armor-grade ceramics with different indenter geometries (Vickers and Knoop) over a range of indentation loads (0.98-98 N) and discuss the implications for armor ceramics. The resulting data strongly indicate that the best means of determining the hardness of armor ceramics is the use of 19.6-N Knoop indentations.     

Instrumented indentation test for advanced technical ceramics

The standard for advanced technical ceramics ENV 843-4 of 1995 (Vickers, Knoop and Rockwell superficial hardness tests) was validated within the framework of the CERANORM EC-project. The paper reports on depth sensing hardness measurements done for comparison with the other hardness tests. The instrumented indentation test is a modern technique (recent issue ISO/DIS 14577) that has the potential to take into account the specific response of materials in a much better way. An evaluation has been made to establish whether the instrumented hardness technique is a appropriate method for advanced technical ceramics and offers potential for additional applications.     

Knoop and Vickers Indentation in Ceramics Analyzed as a Three-Dimensional Fracture

A three-dimensional fracture analysis is applied to the Knoop and Vickers indentation fracture of ceramics. A brief discussion of the accuracy of the analysis applied to model the step load on the crack face caused by the residual stresses is given. A study is made of the effect of the elongated plastic zone in Knoop indentation on the unloaded radial fracture. It is shown that for small indentation loads the published experimental data can be verified by varying the depth reached by the semielliptical plastic zone with given surface length. An analysis and interpretation of the interaction between the two halfpenny-shaped radial cracks induced by Vickers indentation is also given.     

Knoop Microhardness Anisotropy and the Indentation Size Effect on the Basal Plane of Single-Crystal Alumina (Sapphire)

The Knoop microhardness anisotropy profile was determined for the basal plane of a Czochralski grown alumina single crystal for indentation test loads from 100 through 1000 g. Microhardness maxima occur at low indentation test loads for the long axis of the Knoop indenter parallel to the 〈2[Onemacr][Onemacr]0〉. Minima exist for the long axis parallel to the 〈10[Onemacr]0〉. This low indentation test load profile is attributed to slip on the primary slip system, the (0001)〈[Onemacr][Onemacr]20〉, as previously noted by Brookes and co-workers. The degree of the microhardness anisotropy decreases for higher indentation test loads. This results from the activation of multiple slip systems to accommodate the greater amounts of plastic flow required by the larger indentation sizes. The microhardness profile becomes more uniform with increasing indentation test load until the Knoop microhardness approaches a test-load-independent, orientation-independent microhardness of 1167 ± 34 kg/mm². The indentation size effect (ISE) was further investigated through lubricated indentation hardness measurements. Lubrication of the test specimen surface significantly reduces the ISE. Results indicate that friction between the test specimen surface and the indenter facets is a major portion of the ISE.     

Effect of Indenter Geometry on Controlled-Surface-Flaw Fracture Toughness

Fracture toughness values obtained using both Knoop and Vickers-indentation-produced controlled surface flaws were compared as a function of indentation load for a well-characterized glass-ceramic material. At the same indentation load, Knoop cracks were larger than Vickers. As-indented K_c values calculated from fracture mechanics expressions for surface flaws were higher for Knoop flaws than Vickers, but both types gave low K_c values due to indentation residual stress effects. Analysis suggested that theoretical formalisms for indentation residual stress effects based on fracture mechanics solutions for a center-loaded penny crack in an infinite medium should apply to both indentation types. K_c values calculated using the residual stress approach were identical for Knoop and Vickers controlled surface flaws when a "calibration" value for a constant term in the expression for K_c was used for both indentation types.     

Comparison of instrumented Knoop and Vickers hardness measurements on various soft materials and hard ceramics

Vickers and Knoop hardness measurements performed on various ceramics (hard metals) and light alloy materials (soft metals) are compared. The results show that the Knoop hardness number is, in general, lower than the Vickers hardness number for the highest values of hardness, and this behaviour is reversed when the hardness values are low. This change in values, which occur at 8 GPa, has no real physical meaning and, therefore, it is difficult to interpret such behaviour in terms of the elasto-plastic deformation around the indent such as sinking-in, piling-up, and bulging of the indent faces, phenomena which take place during indentation or after the withdrawal of the indenter.Prior to interpreting the hardness difference, it is very important to consider the same area in the hardness calculations. That is why we have compared the available hardness data obtained from the literature and recalculated them by considering the projected and true areas of the contact. If the objective is to compare the two hardness numbers, it seems more suitable to consider the true area of contact, procedure which will provide a Vickers hardness number higher than the Knoop hardness number all over the range of the hardness values.     

Comparison of conventional Knoop and Vickers hardness of ceramic materials

Ceramics generally have a lower Knoop than Vickers hardness. This difference is due to the elastic recovery occurring around a Knoop indentation and the difference in representative area considered to calculate the hardness value.Conventional hardness tests with Knoop and Vickers indenters were performed in order to show how Knoop hardness test can give the same hardness number obtained by Vickers hardness test. This is obtained when Knoop hardness number is calculated based on the residual plastically deformed area whether projected or true. Complementary hardness data obtained from the literature were used in this work in order to validate the method proposed in this work. A revision of the well-known relation of Marshall is proposed in order to determine the elastic modulus by means of one Knoop hardness test when the Vickers hardness is unknown.     

Load-dependence of Knoop hardness of Al2O3–TiC composites

Nine samples of Al₂O₃–30 wt.% TiC composites were prepared by hot-pressing the Al₂O₃ powder mixed with TiC particles. The average sizes of the TiC particles used for preparing the nine samples were different with each other. Knoop hardness measurements were conducted on these nine samples, respectively, in the indentation load range from 1.47 to 35.77 N. For each sample, the measured Knoop hardness decreases with the increasing indentation load. The classical Meyer's power law and an empirical equation proposed originally by Bückle were verified to be sufficiently suitable for describing the observed load-dependence of the measured hardness. Analysis based on Meyer's law can not provide any useful information about the cause of the observed ISE while true hardness values, which are load-independent, can be deduced from the Bückle's equation. It was found that the deduced true hardness increases with the average size of TiC particles existing in the sample.     

Mechanical properties of thermally sprayed porous alumina coating by Vickers and Knoop indentation

Depending on the thermal spraying conditions, coatings obtained can present different defects, like pores, cracks and/or unmelted particles, and different surface roughnesses, that can affect the determination of the hardness and elastic modulus. The present work investigates the mechanical properties, determined by means of Knoop and Vickers indentations, of a plasma as-sprayed alumina coating, obtained with a nano-agglomerated powder sprayed using a PTF4 torch, in order to highlight how the surface defects interfere into the indentation process. As a main result, Knoop indentation compared to Vickers one gives less dispersive results (15% and 33%, respectively), that are, in addition, more representative of the coating properties. The mean values obtained are 110 ± 40 GPa for the elastic modulus and 1.75 ± 0.42 GPa for the hardness. In addition, and for the two indenter types used, multicyclic indentation has been performed because it allows a more appropriate characterization of such heterogeneous coatings due to the representation of the mechanical properties as a function of the indentation load and/or the penetration depth, leading to more reliable results according to the depth-variability of the coating microstructure.     

Indentation responses of viscoelastic materials

Vickers indentation is arguably one of the most widely used techniques for characterizing the mechanical properties of materials because it is easy, inexpensive, and nondestructive. However, its popularity has so far been limited to ceramics and metals, and very little literature information is available on the Vickers indentation properties of high or rigid polymers. In this article, the Vickers indentation responses of an epoxy and acrylic polymer have been studied. The hardness of these materials is found to be time-dependent as a result of viscoelastic flow and relaxation processes. Unlike ductile metals, the microhardness is not dependent on the indentation load. The elastic recovery in the Vickers impression takes place only along the side faces but not along the diagonals. Thus, the use of Vickers indentation as a convenient tool for evaluating the hardness and viscoelastic responses of rigid polymers is justified. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2349–2352, 1998