Factors Resulting In Micron Indentation Hardness Descending In Indentation Tests

Some factors that affect the experimental results in nanoindentation tests such as the contact depth, contact area, load and loading duration are analyzed in this article. Combining with the results of finite element numerical simulation, we find that the creep property of the tested material is one of the important factors causing the micron indentation hardness descending with the increase of indentation depth. The analysis of experimental results with different indentation depths demonstrates that the hardness decrease can be bated if the continuous stiffness measurement technique is not adopted; this indicates that the test method itself may also be one of the factors causing the hardness being descended.

社会发展与中国人人格变迁——控制测验理论与工具的变异后不同时期的中国人人格差异研究

In non-western society，researches on social development and personality change focused on economic development and social modernization. The present study is aimed at exploring the relationship between the social transformation and personality changes of Chinese people by using so-called indigenous personality measurement of CPAI (Chinese Personality Assessment Inventory). Meanwhile, the influence of CPAI measurement itself and measurement theory were also taken into consideration. In study 1, two sets of CPAI data collected in a 10 year interval were analyzed. At the same time, the CPAI-2 data was analyzed in terms of modernization level of various cities from which the data were collected. However, this study didn’t consider the importance of “equivalence” of the measurement, CPAI. In study 2, we detected DIF (Differential item functioning) across the different period groups to confirm if CPAI was equal to people in different period. In this process, both CTT and IRT method were used. The outcome reminded us that there were some DIF items. In study 3, to make sure that the personality measurement is fair to people in different period, we only saved those items whose DIF effect size lower than 0.01, and used IRT method to estimate test-taker’s personality. Then, cohort analysis was used to explore the pattern of personality change of Chinese people. In study 4, we factor-analyzed the DIF items to find the relation between social transformation and the latent personality variable which were composed of DIF items. From these 4 studies, we could got the following conclusions: (1) The CPAI 22 traits could be divided into two categories, with the changing of age, period and cohort, type I traits didn’t change, they were Logical vs Affective Orientation, Enterprise, Responsibility, Inferiority vs Self-Acceptance, Optimism vs Pessimism, Face, Family, Defensive, Graciousness vs Meanness; While with the changing of age, period and cohort, type II traits changed, they were Leadership, Self vs. Social Orientation, Veraciousness vs Slickness, Traditionalism vs Modernity, Harmony, Renqing, Meticulousness, Extraversion vs Introversion, Emotionality, Practical Mindedness, Internal vs External Locus of Control, Thrift vs Extravagance, Discipline. Meanwhile DIF items measured 5 psychologycial characteristics which changed greatly with the changing of age, period and cohort, they were Life attitude of Cynicism-realism, Psychological maladjustment, Coping style of Waiyuanneifang, Self-efficacy, the value of Individualism. (2) In sum, Chinese people in 1992 were more traditional than those in 2001, and with the 10-year of rapid development, according to the market economy’s needs, Chinese people became more individualism. (3) The DIF method of CTT and IRT were comparable. But, in generally, IRT method was more accurate and valid in detecting DIF as were as estimating personality. (4) The DIF outcomes showed that CPAI had good item validity. Meanwhile, it’s possible to develop a subscale by using CPAI items to assess some psychological characteristics. In this current study, according to their stability and variability, we could divided personality traits and psychological characteristics into 3 categories, and the outcome supported the hypothesis of “Six Factor Model”, these foundings were of some theoretic meanings. Meanwhile, as the relation between social development and personality change being explored, it certain help Chinese people cope with the rapid changing society. In this study, we also found that it’s possible to develop a subscale by using CPAI items to assess obverse personality traits and it had some practical use. Furthermore, the use of different measurement theory and cohort analysis embodied some innovation in methodology.

心理旋转中的整体优先效应及其机制

In the history of psychology research, more attention had been focused on the relation between local processing and global processing. For the global information and the local information, which is processed earlier? And which is processed faster? Precedence of the global over the local level in visual perception has been well established by Navon with compound stimuli, and Navon’s original study gave rise to many publications, including replications, generalization to other kinds of stimuli (nonverbal material, digits), populations (infants, children, brain-damaged subjects), and tasks (lateral visual hemifield presentation, copy drawing, memory recognition, and recall), and triggered some debate about the conditions in which global precedence is and is not observed (number, size, sparsity, and goodness of the stimuli, exposure duration, etc.). However, whether there is a global advantage or precedence in other cognitive processes was less tested. Most researches had suggested that there was a functional equivalency between visual perception and visual image processing. However, it’s still unknown whether there will be a global advantage on mental rotation. In the present study, we combined the mental rotation task with the compound stimuli to explore whether the global or local advantage also existed at the mental imagery transformation stages. In two pilot studies, the perceptual global precedence was found to be present in a normal/mirror-image judgment task when the stimuli exposure time was short; while the stimuli exposure time was prolonged (stimuli kept available till subjects’ response) the perceptual global precedence was showed to be eliminated. In all of the subsequent experiments, stimili would be presented till subjects’ response. Then mental rotation was added in normal/mirror-image judgment (some of the stimuli were rotated to certain angles from upright) in normal experiments, experiment 1 and 2 observed a global advantage on mental rotation both with a focused-attention design (Experiment 1) and divided-attention design (Experiment 2). Subjects’ reaction times were increased with rotation angles, and the accuracy was decreased with rotation angles, suggesting that subject need a mental rotation to make a normal/mirror judgment. The most important results were that subjects’ response to global rotation was faster than that to local rotation. The analysis of slope of rotation further indicated that, to some extend, the speed of global rotation was faster than that of local rotation. These results suggest a global advantage on mental rotation. Experiment 3 took advantage of the high temporal resolution of event-related potentials to explore the temporal pattern of global advantage on mental rotation. Event-related potential results indicated the parietal P300 amplitude was inversely related to the character orientation, and the local rotation task delayed the onset of the mental-rotation-related negativity at parietal electrodes. None clear effect was found for occipital N150. All these results suggested that the global rotation was not only processed faster than local rotation, but also occurred earlier than local rotation. Experiments 4 and 5 took the effect size of global advantage as the main dependent variable, and visual angle and exposure duration of the stimuli as independent variables, to examine the relationship between perceptual global precedence and global advantage on mental rotation. Results indicated that visual angle and exposure duration did not influence the effect size of global advantage on mental rotation. The global advantage on mental rotation and the perceptual global advantage seemed to be independent but their effects could be accumulated at some condition. These findings not only contribute to revealing a new processing property of mental rotation, but also deepen our understanding of the problem of global/local processing and shed light on the debate on locus of global precedence.

学习不良少年的污名效应研究

Stigma is defined as a sign of disgrace or discredit that sets a person apart from others. Stigmatized individuals had been significantly influenced by their group-based stigma. Through the methods of laboratory experiment and questionnaire surveys, the current study started with examining the attitudes of middle school students to the students with learning disabilities (LD), systemly explored the characteristics of perceived stigma and self-stigma of LD students, the mechanism that the influences of stigma on students with LD, and the mental control required to cope with the stigma. The results of the present studies had significant implications for the understanding of the LD phenomenon and the intervention of LD adolescents. The results indicate that: 1. Generally, middle school students had negative implicit attitude and negative explicit attitudes towards the LD students. The effect size of the phenomenon of this study is large. The LD students showed a more positive attitude than others on the explicit attitude measure; all students consistently had negative attitudes toward LD students on the implicit attitude indices, in addition, no group differences and gender differences were observed in the implicit attitude. 2. Eight hundred and seventy two students were surveyed to test the reliability and validity of the new developed perceived stigma scale and self-stigma scale. Both questionnaires showed sufficient content validity, construct validity, criterion-related validity and adequate internal consistency reliability. Then, both questionnaires were administered to student with high academic achievement (high achiever), students with middle academic achievement (middle achiever), and LD students. Results revealed that the LD students mildly stigmatized by the social culture. The LD students had more stigma perception and self-stigma than the middle achievers and high achievers. The results also indicated that there were more stigma perception and self-stigma for LD students in grade two than that of LD students in grade one and grade three; meanwhile, male LDstudent hade more stigma perception and self-stigma than female LD students in all grades. 3. A latent variable path analysis was conducted to investigate how the stigma affect the academic goals using the data collected from 186 LD students. The results suggested that the LD-related stigma did not have direct influence on academic goals. The LD-related stigma indirectly influenced the academic goals through mediating effects of self-stigma and academic efficacy. 4. Stereotype threat could have some influences on the relationship between the task feedback and self-esteem. The results of study using eighty-four LD students showed that: when the negative stereotype was not primed, the self-esteem of the LD students was significantly influenced by the feedback of the task: an enhance self-esteem following a positive feedback and a lower self-esteem following a negative feedback. When the negative stereotype was primed, there was no significantly difference between the positive feedback group and negative feedback group. All the results showed that priming the negative stereotype could weaken the influence of feedback to the self-esteem of LD students. 5. There was more cognitive and behavioral control when LD students tried to cope with the stigma by concealing negative academic achievement during an individual interview with an unfamilar expert. The LD students whose academic achievements could be concealed had more thought suppression and thought intrusion and reported more self-monitoring behavior than the participants in the other experimental conditions.

Effect of Rock Mass Structure and Block Size on the Slope Stability-Physical Modeling and Discrete Element Simulation

This paper studies the stability of jointed rock slopes by using our improved three-dimensional discrete element methods (DEM) and physical modeling. Results show that the DEM can simulate all failure modes of rock slopes with different joint configurations. The stress in each rock block is not homogeneous and blocks rotate in failure development. Failure modes depend on the configuration of joints. Toppling failure is observed for the slope with straight joints and sliding failure is observed for the slope with staged joints. The DEM results are also compared with those of limit equilibrium method (LEM). Without considering the joints in rock masses, the LEM predicts much higher factor of safety than physical modeling and DEM. The failure mode and factor of safety predicted by the DEM are in good agreement with laboratory tests for any jointed rock slope.

Size Effect and Geometrical Effect of Polycrystals and Thin Film/Substrate System in Micro-indentation Test

Micro-indentation test at scales on the order of sub-micron has shown that the measured hardness increases strongly with decreasing indent depth or indent size, which is frequently referred to as the size effect. Simultaneously, at micron or sub-micron scale, the material microstructure size also has an important influence on the measured hardness. This kind of effect, such as the crystal grain size effect, thin film thickness effect, etc., is called the geometrical effect by here. In the present research, in order to investigate the size effect and the geometrical effect, the micro-indentation experiments are carried out respectively for single crystal copper and aluminum, for polycrystal aluminum, as well as for a thin film/substrate system, Ti/Si3N4. The size effect and geometrical effect are displayed experimentally. Moreover, using strain gradient plasticity theory, the size effect and the geometrical effect are simulated. Through comparing experimental results with simulation results, length-scale parameter appearing in the strain gradient theory for different cases is predicted. Furthermore, the size effect and the geometrical effect are interpreted using the geometrically necessary dislocation concept and the discrete dislocation theory. Member Price: $0; Non-Member Price: $25.00

Effect of Particle Size on the Formation of Adiabatic Shear Band In Particle Reinforced Metal Matrix Composites

In this paper, the effect of particle size on the formation of adiabatic shear band in 2024 All matrix composites reinforced with 15% volume fraction of 3.5, 10 and 20 mum SiC particles was investigated by making use of split Hopkinson pressure bar (SHPB). The results have demonstrated that the onset of adiabatic shear banding in the composites strongly depends on the particle size and adiabatic shear banding is more readily observed in the composite reinforced with small particles than that in the composite with large particles. This size dependency phenomenon can be characterized by the strain gradient effect. Instability analysis reveals that high strain gradient is a strong driving force for the formation of adiabatic shear banding in particle reinforced metal matrix composites (MMCp).

Size Effect and Geometrical Effect of Solids in Micro-Indentation Test

Micro-indentation tests at scales of the order of sub-micron show that the measured hardness increases strongly with decreasing indent depth or indent size, which is frequently referred to as the size effect. At the same time, at micron or sub-micron scale, another effect, which is referred to as the geometrical size effects such as crystal grain size effect, thin film thickness effect, etc., also influences the measured material hardness. However, the trends are at odds with the size-independence implied by the conventional elastic-plastic theory. In the present research, the strain gradient plasticity theory (Fleck and Hutchinson) is used to model the composition effects (size effect and geometrical effect) for polycrystal material and metal thin film/ceramic substrate systems when materials undergo micro-indenting. The phenomena of the "pile-up" and "sink-in" appeared in the indentation test for the polycrystal materials are also discussed. Meanwhile, the micro-indentation experiments for the polycrystal Al and for the Ti/Si_3N_4 thin film/substrate system are carried out. By comparing the theoretical predictions with experimental measurements, the values and the variation trends of the micro-scale parameter included in the strain gradient plasticity theory are predicted.

A Molecular Dynamics Simulation: the Effect of Finite Size on the Thermal Conductivity in a Single Crystal Silicon

Non-equilibrium molecular dynamics (NEMD) simulations are performed to calculate thermal conductivity. The environment-dependent interatomic potential (EDIP) potential on crystal silicon is adopted as a model system. The issues are related to nonlinear response, local thermal equilibrium and statistical averaging. The simulation results by non-equilibrium molecular dynamics show that the calculated thermal conductivity decreases almost linearly as the film thickness reduced at the nanometre scale. The effect of size on the thermal conductivity is also obtained by a theoretic analysis of the kinetic theory and formulas of the heat capacity. The analysis reveals that the contributions of phonon mean free path (MFP) and phonon number in a finite cell to thermal conductivity are very important.

Inverse Grain-Size Effect On Twinning In Nanocrystalline Ni

A long-standing controversy exists between molecular dynamics simulations and experiments on the twinning propensity of nanocrystalline (NC) face-centered-cubic metals. For example, three-dimensional molecular dynamics simulations rarely observed twins in NC Ni, whereas experiments readily observed them. Here this discrepancy is resolved by experimental observation of an inverse grain-size effect on twinning. Specifically, decreasing the grain size first promotes twinning in NC Ni and then hinders twinning due to the inverse grain-size effect. Interestingly, no inverse grain-size effect exists on stacking fault formation. These observations are explained by generalized planar fault energies and grain-size effect on partial emissions.

Investigation on mechanical properties and size effect of nanocrystalline twin copper

The stress-strain relations of nanocrystalline twin copper with variously sized grains and twins are studied by using FEM simulations based on the conventional theory of mechanism-based strain gradient plasticity (CMSG). A model of twin lamellae strengthening zone is proposed and a cohesive interface model is used to simulate grain-boundary sliding and separation. Effects of material parameters on stress-strain curves of polycrystalline twin copper are studied in detail. Furthermore, the effects of both twin lamellar spacing and twin lamellar distribution on the stress-strain relations are investigated under tension loading. The numerical simulations show that both the strain gradient effect and the material hardening increase with decreasing the grain size and twin lamellar spacing. The distribution of twin lamellae has a significant influence on the overall mechanical properties, and the effect is reduced as both the grain size and twin lamellar spacing decrease. Finally, the FEM prediction results are compared with the experimental data.

Effect of grain size on slow fatigue crack propagation and plastic deformation near crack tip

Fatigue crack growth and its threshold are investigated at a stress ratio of 0.5 for the three-point bend specimen made of Austenitic stainless steel. The effect of grain size on the crack tip plastic deformation is investigated. The results show that the threshold value Δkth increases linearly with the square root of grain size d and the growth rate is slower for materials with larger grain size. The plastic zone size and ratio for different grain sizes are different at the threshold. The maximum stress intensity factor is kmax and σys is the yield strength. At the same time, the characteristics of the plastic deformation development is discontinuous and anti-symmetric as the growth rate is increased from 2·10—8 to 10−7 mm/cycle.

Interface cracking and particulate size effect in particle-reinforced metal-matrix composites

The mechanical behaviors of the ceramic particle-reinforced metal matrix composites are modeled based on the conventional theory of mechanism-based strain gradient plasticity presented by Huang et al. Two cases of interface features with and without the effects of interface cracking will be analyzed, respectively. Through comparing the result based on the interface cracking model with experimental result, the effectiveness of the present model can be evaluated. Simultaneously, the length parameters included in the strain gradient plasticity theory can be obtained.