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For the normal penetration of a symmetrical rigid projectile into a concrete target with coarse aggregates, the lateral deflection may occur under certain conditions depending on geometrical parameters of the projectile, impact velocity and coarse aggregate distribution. In this work, four dimensionless numbers of projectile, that is, impact factor [Formula: see text], length-to-diameter ratio [Formula: see text], nose factor [Formula: see text] and the relative location of mass center [Formula: see text], are employed to study the effects of projectile parameters on the deflection of penetration trajectory. Numerical studies based on three-dimensional (3D) meso-scale concrete model are conducted and the projectile trajectories are obtained under different dimensionless numbers. According to the development of the deflection angle during the rigid projectile penetration into meso-scale concrete, the motion of the projectile can be divided into four stages, that is, initial deflection, rapid change, deflection rebound and final stage. The numerical results show that, for the same meso-scale concrete target, the deflection of the projectile trajectory becomes larger with the increases of [Formula: see text], [Formula: see text] and [Formula: see text], while the deflection angle of projectile decreases with the increase of [Formula: see text].

In this study, a dynamic indentation test method based on the split Hopkinson pressure bar is proposed to obtain the dynamic parameters of Ludwik power law constitutive, namely, Young’s modulus E, strength coefficient K, and strain hardening index n by analyzing dynamic indentation load-indentation depth curve obtained from the theories relating to the Hopkinson pressure bar. The important parameters, namely, loading curvature C and transformation factor [Formula: see text], are invoked to examine the dynamic indentation response results in a wide range of target material parameters. Finite element calculation results are processed through simulation of dynamic indentation response with broad material parameters. Furthermore, the analytical method is used to fit simulation results to obtain the analytical equations for elastic–plastic parameters and curvature parameters for the subsequent analysis. The analytical equation of forward model to predict dynamic indentation response parameter–loading curvature C of a known material is proposed. Then, the elastic–plastic parameters of unknown materials (according to Ludwik power law) are obtained by substituting the dynamic indentation response parameters into an inverse analytical equation under the two types of half-cone angle indenters. The method is verified by other typical materials, which shows that the dynamic indentation test based on the split Hopkinson pressure bar can obtain sufficient conditions to obtain dynamic mechanical properties of target materials.

Nanoindentation tests were performed at room temperature to investigate the indentation size effect (ISE) and creep behavior of a titanium metallization film on alumina substrate. The ISE of hardness was examined at different loading strain rate (LSR). The effects of LSR and penetrating depth on nanoindentation creep were evaluated at the steady creep state. Inverse ISE in titanium film was observed at indentation depth below 200 nm while normal ISE was observed at penetrating depth ranging from 200 nm to 1000 nm. Elastic contact theory and strain gradient plasticity theory were applied to interpret the variation trends of hardness respectively. In addition, the intrinsic hardness and characteristic length were found to be strongly dependent on LSR. Except for creep strain rate, creep displacement and creep stress exponent showed relatively conspicuous correlations to LSR and/or penetrating depths.

In this paper, nanoindentation test of zirconia ceramics was carried out under different strain rates by continuous stiffness measurement (CSM) technique at room temperature. This work aimed at studying the influence of indentation size effect (ISE) on strain rate sensitivity (SRS). The results showed that the contact stiffness increased almost linearly with the depth of the indentation. Under different strain rates, the contact stiffness and elastic modulus remain basically unchanged, but the hardness increases with the increase of the strain rate. The SRS exponent m is strongly dependent on the indentation depth. A calculation method for nano-hardness without ISE was proposed by detecting the relationship between hardness and indentation depth.

Quasi-static indentation tests were conducted to characterize the mechanical behavior of honeycombs. The local failure mechanisms of honeycombs with different relative density were discussed in det...

Epoxy-based isotropic conductive adhesives (ICA) have become the dominant materials in the microelectronic packaging field due to their advantages of low technological temperature, ultrafine line p...

In this investigation, an asymmetrical yield criterion is proposed, and applies it to a hardness model which considers the interaction between statistically stored dislocations (SSDs) and geometrically necessary dislocations (GNDs). Based on this modified model, the relationship between pre-compression strain and hardness is analyzed by nanoindentation tests. In order to obtain the yield behavior of the CoCrFeNiMn high entropy alloy (HEA), the combined loading and uniaxial loading tests are conducted. Then different compression plastic strain is applied to specimens under various levels of temperature to investigate the interaction between SSDs and GNDs of CoCrFeNiMn HEA. Finally, the result shows that the effect of pre-compression depends on the competition between the pre-compression induced dislocations and nanoindentation nucleated dislocations because pre-compression causes the change of grain size.

Dynamic uniaxial and multiaxial tests were conducted to characterize the mechanical behavior of poly(methyl methacrylate) (PMMA). In this case, the multiaxial yield behavior of materials can be captured by the shear-compression samples (SCS). The experimental results were compared with different yield criteria, and which does not have a good agreement between theoretical prediction and experimental yield loci of PMMA undergoing combined shear-compression. Therefore, a phenomenological yield criterion is developed, and it notably involves hydrostatic stress sensitivity, lode angle, and one parameter. The parameter can be expressed by the asymmetry of yield strength between the tension and compression. The proposed criterion was verified by the utilization of differently combined shear-compression tests. The investigative results reveal that the proposed criterion can be successfully applied to describe the complex yield behavior of PMMA under dynamic loading conditions. The present study shows an efficient method to develop yield criterion of the reviewed materials.

A series of uniaxial and triaxial experiments are performed to analyze the mechanical behavior of foamed concrete (FC). The experimental results indicate that for uniaxial loading, foamed concrete demonstrates brittle failure under a uniaxial tension and small compression deformation. A 1D damage constitutive model is then established and expected to predict the nonlinear responses of foamed concrete under a large compression deformation. For triaxial loading, the level of confining pressure significantly influences the multiaxial mechanical behavior of foamed concrete due to its hydrostatically compressible characteristic. An elliptic phenomenological yield criterion based on three loading paths is further proposed and extended to consider the density-dependent effect by modifying the corresponding material constants as a function of material density. The comparisons between the theoretical predictions and experimental results reveal that the present yield criterion can give a good description of the tension/compression asymmetry, pressure dependence, and density sensitivity of the yield loci under the effective stress-mean stress space.

ZrB2 based ultra-high temperature ceramic (UHTC) is one of the most promising materials for thermal protection systems. This paper focuses on the oxidation behaviors of ZrB2 under compressive stress. ZrB2 UHTC is fabricated with nano-sized powders at 1500 °C, which is a relative low temperature. Nanoindentation tests are conducted to measure the basic mechanical properties of sintered samples. Results of nanoindentation show that ZrB2 is prepared with good mechanical properties. Oxidation tests are performed under different stress states and temperatures, and oxidation mechanisms and microstructure evolution are discussed. As the oxidation proceeds, ZrO2 grains grow slowly at 1000 °C, but fast at 1200 °C. When oxidized over 1400 °C, ZrO2 grains fuse and micro-sized pores form on the surface due to the release of gaseous oxidation products. The thickness of oxide layer on the samples almost keeps unchanged under various compressive loads. Compared with the stress state, microstructure has a more obvious effect on the oxidation rate. The results in this paper provide a better understanding on the oxidation mechanism of ZrB2 based UHTCs.

In this paper, the anisotropic mechanical properties of rolled AZ31 magnesium alloys are investigated using nanoindentation tests at room temperature. Nanoindentation was carried out at four angles, including the rolling direction (0&deg, ), diagonal direction (45&deg, ), transverse direction (90&deg, ), and vertical direction (ND). Experimental results show that hardness increases as the rolling angle increases from 0&deg, to 90&deg, and is lowest in the ND direction. The hardness independent of the effect of indentation depth is obtained by analyzing the indentation size effect and then converting hardness values into yield strengths. A new criterion is proposed on the basis of the Hill48 yield criterion. The data obtained through the above experiments are used to determine the parameters in the new criterion. Finally, a solution to the challenge of modeling a function that accurately describes the anisotropic yielding behavior of AZ31 magnesium alloys is proposed using the nanoindentation technique to solve the requirements of specimen size and experimental methods of the macro test.

It is very important to minimize the residual velocity of penetrator as far as possible in designing defensive structures. The ability of reinforced concrete (RC) against projectile penetration can be effectively promoted by optimizing the configuration of reinforcement. This paper presents numerical studies on the penetration resistance of RC against non-deforming projectile penetration at striking velocities ranging from 300 m/s to 1056 m/s. Firstly, an innovative three-dimensional (3D) meso-scale model of RC is created and the randomness of the shape, size and distribution of aggregates are taken into account. A modified intersection detection is used to prevent the aggregates from overlapping with embedded reinforcements. In order to validate the RC model and analysis approach, the numerical results of penetration are compared with the referenced experimental data, and good agreements are obtained. Numerical studies based on the validated meso-scale model are conducted to investigate the effects of reinforcement on the anti-penetration performance of slabs under different impact positions and reinforcement configurations, focusing on the reinforcement ratio, size of reinforcing meshes, distribution location (front, middle and rear), buried depth of the first layer, interlayer spacing and the number of reinforcing layers. Finally, the validations of numerical perforation results on ballistic limit are assessed by comparing with some empirical formulae. The results also show that the distributed aggregate is an important factor affecting the penetration resistance of RC.

The compression, tension, shear and combined shear-compression tests with different loading rates were conducted to investigate the mechanical behaviour of PA66 specimens. The initial yield and post-yield behaviour were analysed to determine the parameters in theoretical models. Results showed that the yield criterion based on three stress invariants gives the best description of the initial yield behaviour of PA66. The post-compression/tensile behaviour of PA66 was described by a hyperbolic function. The subsequent yield function was proposed based on the combination of initial yield surface and mixed work hardening model. The ratio of compression and tensile strength was utilized to appropriately characterize the kinematic hardening. Additionally, the effects of loading rate on PA66 yield stress and post-yield behaviour can be described by Eyring theory. On the basis of the general observations and classical elastoplastic theory, a macroscopic phenomenological constitutive was constructed to describe the mechanical behaviour of PA66.

Quasi-static compression, tension and combined shear–compression tests were conducted to characterize the mechanical behavior of PMMA. The cylinder samples and dog-bone samples were used for uniaxial testing. The shear–compression samples of four different angles (15°, 30°, 45°, and 50°) were used to obtain the multiaxial stress state instead of complex loading equipment. The yield behaviors of PMMA cannot be described by the Tresca or Mises criterion due to the effects of both the first invariant of the stress and the third invariant of deviatoric stress. A criterion is proposed that includes the first invariant of the stress and the third invariant of deviatoric stress in this paper. In other word, the effects of hydrostatic pressure and Lode angle are considered. The proposed yield criterion has the capability to precisely capture the experimental yield loci of PMMA.

Surface titanium (Ti) metallization was conducted on alumina (Al2O3) through chemical vapor deposition (CVD) method derived from non-contact pack cementation. The effects of different deposition temperature (1000 °C, 1050 °C, and 1100 °C) were examined in this scenario. The morphology, phase composition, and interfacial defects of the resulting films were systematically investigated through scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The nanomechanical characterization of the proposed thin films was evaluated by conducting nano-indentation tests at different depths. The results revealed that uniform Ti films were coated on the Al2O3 substrate. During coating, the atoms on the matrix surface were driven to form different structure due to different deposition temperature, leading to disparate morphologies of the surface and the interface, which consequently influenced the binding force between the film and the substrate. Moreover, the nanomechanical properties were found to be related to the internal and interface structure. Decreased modulus and hardness were obtained for metallization films treated at 1050 °C, and plastic deformation was the main deformation pattern.

An effective numerical method is proposed in this paper to generate a meso-scale composite model of reinforcement concrete (RC) which contains aggregates with random size and shape based on Voronoi tessellation method. Besides the randomly distributed aggregates, the present model takes into account the reinforcement, compared with other conventional methods in finite element modeling of concrete. The shrinking algorithm with random shrinking factors is employed to generate graded aggregates. A simple and effective intersection detection is used for aggregate-reinforcement to prevent the aggregates from overlapping with preset reinforcements, but it is unnecessary for aggregate-aggregate due to the characteristic of Voronoi technique. The artificial layer with random offset distance is adopted to simulate the minimum gap between two adjacent aggregates, and the high-volume fraction model is obtained by the sinking process. In order to verify the reliability of the RC model, the numerical results of penetration are compared with the referenced experimental data, and good agreements are obtained. It is indicated that the proposed model can simulate and explain qualitatively the effects of the meso-scale structural properties on the macroscopic dynamic response of RC. Furthermore, this method has great significance in performance analysis, structural optimization and material design for RC composites.

In this paper, quasi-static compression, tension, shear and combined compression-shear tests are conducted on cast AZ91 magnesium alloy in order to study its yield behavior. For the combined compression-shear tests, shear-compression specimens (SCS) are employed to generate the additional shear stresses, instead of complex loading device. Results show that the SCS is an effective method to obtain experimental results with different stress states. Tresca and von-Mises criterions cannot give an appropriate description of the yield behaviors of AZ91 Mg alloy because of its dependence on hydrostatic pressure and Lode angle. A criterion was used, which contains three invariants of the stress and deviatoric stress, and in which the second invariant of deviatoric stress and the first invariant of the stress are correlated quadratically. This criterion can describe the experimental yield loci of AZ91 Mg alloy.

Epoxy-based conductive adhesives have been widely used in the electronic field given the lead-free development of electronic packaging. The conductive adhesive joints must be subjected to shear loa...

Effective acquisition of the related mechanical properties of lead-free solder alloys through micro-indentation tests is of great significance in the research on electronic interconnection design and reliability for the multi-functionalization and high integration of electronic products. The temperature-dependent elastoplastic and creep parameters of Sn–3.0Ag–0.5Cu (SAC) solder are systematically investigated by micro-indentation with plural indenters and the “rapid loading-holding-rapid unloading” test mode. Based on the depth dependence of indentation hardness from mechanism-based strain gradient plasticity and the stress independence of creep compliance for linear viscous assumption, the complete indentation load-depth curves eliminating the indentation size effect of SAC solder under different temperature and two pyramidal indenters with different equivalent semi-cone angles are reconstructed. Combining with the temperature-dependent elastic modulus measurements from cylindrical indentation, corrected load-depth curves for pyramidal indentation, and the concept of representative stress and representative plastic strain, the elastoplastic parameters eliminating the indentation size effect under different temperature are uniquely determined through numerical simulation and inversion analysis, as well as the corresponding creep parameters. The temperature dependence of elastoplastic and creep parameters of SAC solder is analyzed, and related deformation mechanism is discussed. Results of forward and inverse analyses indicate the effectiveness of proposed characterization method.

Nanoindentation analysis was proposed on a ductile film/hard substrate system to extract the elastoplastic properties of thin film. Based on the dimensional analysis method (DAM), relationships between the indentation responses and film/substrate elastoplastic properties were established. Reverse analysis algorithms were proposed by introducing the substrate effects, which could provide sufficient information at different indentation depths to solve the dimensional equations. Numerical and instrumental indentations were carried out on a titanium film/alumina ceramic substrate system to verify the proposed reverse method, by which the elastic modulus, yield stress and work hardening exponent of the film were successfully obtained.

As concrete and mortar materials widely used in structural engineering may suffer dynamic loadings, studies on their mechanical properties under different strain rates are of great importance. In this paper, based on splitting tests of Brazilian discs, the tensile strength and failure pattern of concrete and mortar were investigated under quasi-static and dynamic loadings with a strain rate of 1–200 s−1. It is shown that the quasi-static tensile strength of mortar is higher than that of concrete since coarse aggregates weaken the interface bonding strength of the latter. Numerical results confirmed that the plane stress hypothesis lead to a lower value tensile strength for the cylindrical specimens. With the increase of strain rates, dynamic tensile strengths of concrete and mortar significantly increase, and their failure patterns change form a single crack to multiple cracks and even fragment. Furthermore, a relationship between the dynamic increase factor and strain rate was established by using a linear fitting algorithm, which can be conveniently used to calculate the dynamic increase factor of concrete-like materials in engineering applications.

Cured isotropic conductive adhesive (ICA) with different conductive fillers (micro silver flakes) contents were prepared. Based on the loading mode of “rapid loading-holding-rapid unloading” and semi-empirical method from the generalized Kelvin model, micro-indentation tests were carried out to investigate the effect of hygrothermal aging on the mechanical properties of cured ICA. On the whole, the elastic modulus and hardness of cured ICA with high silver content are relatively larger. As the hygrothermal aging time increases, both elastic modulus and hardness decrease at first and then stabilize, and the creep deformation is more evident. Indentation creep displacement–time curves for cured ICA were characterized by the generalized Kelvin model. During the holding stage, creep compliance increases slowly at first and then increases quickly with modulus loss. With the aggravated aging creep compliance increases, and creep compliance of cured ICA with high silver content increases faster at the later stage of hygrothermal aging. The widened retardation peaks with increasing retardation time reflect the different retardation processes during the holding stage. With increasing aging time, the creep rate sensitivity exponent increases and creep resistance reduces accordingly.

Two kinds of innovative re-entrant and hexagonal cell honeycomb sandwich structures filled with reactive powder concrete were proposed, and the ballistic resistance and energy absorption of the sandwich structures were investigated by numerical simulations. The deformation and failure modes of the different structures were analyzed and evaluated in detail. The honeycomb sandwich structures filled with reactive powder concrete prisms improved the capacity of ballistic resistance and energy absorption significantly, compared to the normal reactive powder concrete plates and sandwich structures without reactive powder concrete prisms. The analysis shows that the auxetic re-entrant cell honeycomb sandwich structures have a better ballistic performance than the hexagonal cell honeycomb sandwich structures. The sandwich structures were subjected to impact by three kinds of projectiles: flat, hemispherical and conical nosed. The ballistic limit of the flat nosed projectile is the highest, while the impact performance of the conical and hemispherical nosed projectiles is obviously different from the flat nosed projectile, especially in a relative high velocity range. The sharper nose leads to a higher value of exit velocity and mass loss. In addition, effects of different design parameters on ballistic resistance were also studied by changing the thickness of honeycomb cell and face plates. Results indicate that the thickness of honeycomb walls and face plates have significant effect on the ballistic resistance and energy absorption in a relative low velocity range, while there are no big differences when the initial impact velocity exceeds 400 m/s.

Based on the elongated Voronoi models, the yield behaviors of transversely isotropic foams have been explored by using finite element method. A pressure-dependent phenomenological constitutive model (stress potential function) has been established for transversely isotropic foams through the characteristic stress and strain. The stress potential function and its evolution can be determined in terms of the uniaxial and equi-triaxial tensile/compressive characteristic stress-strain curves. The stress potential function is expected to predict the elastoplastic mechanical responses of transversely isotropic foams. The material properties (i.e., relative density, transversely isotropic degree, matrix material and cell morphology) exhibit significant influence on the profile of initial yield surfaces. The pressure dependence of yield surfaces decreases as the relative density and transversely isotropic degree increase. The predictions of pressure-dependent constitutive model match excellently with the simulated yield data under different stress states and characteristic strain stages.