Compressive Plastic Research Articles

Structural rejuvenation and toughening of bulk metallic glass via ultrasound excitation technique

Bulk metallic glasses (BMGs) represent a class of solid materials which have randomly packed atomic structure in long range but exhibit unique properties. Nowadays, the macroscopic brittleness at ambient temperature is the fundamental and intriguing issue to impede the engineering application of BMGs. In this article, we report a breakthrough in solving the strength-ductility tradeoff dilemma of BMGs by introducing strong forced vibration of atoms named ultrasonic vibration (USV) technique. We find that not only the ambient temperature compressive plasticity is remarkably increased but also yield strength is augmented by kHZ level USV treatment. The toughening of BMGs has also been evidenced by the pronounced increase in the first pop-in event, which represents by the critical stress to stimulate the initial yield with the formation of shear band. It has also been confirmed that the free volume in USV treated BMGs is strikingly increased. Therefore, the intrinsic mechanism of USV induced toughening can be interpreted in the frame of structural heterogeneities and energy landscape theory, i.e., the USV induced structural rejuvenation by increasing the loosely packed soft regions and decreasing the closely packed hard regions. The basins that possess larger potential energies are overwhelmingly increased after USV treatment. Our findings provide a new approach for surmounting strength-ductility trade-off dilemma of single atom glassy matter such as BMGs.

Deformation behavior of nanoscale Al–Al2Cu eutectics studied by in situ micropillar compression

Deformation behavior of nanoscale laser processed Al–Al2Cu eutectics at room temperature is characterized through in situ micro-pillar compression testing in a scanning transmission microscope. Interlamellar spacing of Al–Al2Cu eutectics varies from hundreds of nanometers to 20 nm. Three different sizes of micro-pillars are fabricated in order to study the deformation behaviors of single colony and multiple colonies, corresponding to the single crystal and polycrystal respectively. For single colonies, lamellar orientations parallel, normal or inclined to the loading direction were tested. The main findings are: 1) the plasticity mechanisms strongly depend on loading orientation: buckling and kinking in the parallel-loaded eutectics, planar sliding along Al–Al2Cu lamellar interfaces in the incline-loaded eutectics and localized shearing in the normal-loaded eutectics. 2) the incline-loaded eutectics exhibits the lowest compression flow strength, and the normal-loaded eutectics has the highest compression flow strength. 3) with decreasing inter-lamellar spacing, the strength increases and plasticity is uniformly distributed, as opposed to shear localization. Highest compressive plasticity is observed in polycrystalline eutectics with an ensemble of lamellar orientations with ~20 nm average spacing: 17.9% at flow stress of 1.63 GPa, and degenerate, bimodal morphology: 11.1% at flow stress of 1.36 GPa.

A novel steel damping system for rockfall protection galleries

A new steel damping device is proposed to achieve an effective solution for rockfall protection galleries. The system consists of an assembly of cold-formed steel crash boxes, namely Collapsible Tubular Element (CTE), with a transversal section and a length designed to assure, under axial loads, a compressive plastic deformation (folding) without the need of any guide means. Assembled in groups to create a modular cushion, the system reduces the deceleration and the derived impact force due to an impacting block mass during a rockfall event. The influence of both the system module configuration (number of CTEs, presence of restraining cables) and the boulder parameters (mass, angle, and velocity at the impact) is investigated, and a Dynamic Finite Element analyses, along with a full-scale experimental test, have been carried out to evaluate the system performances. The obtained results indicate how the proposed system mitigates the dynamic amplification of the forces transmitted from the impact point to the roof slab, with a mean value of the impact force increased by only 2% within the damping cushion, showing, if compared with the mainly adopted damping cushion systems, a drastic reduction of both impact force and dead load on the gallery's roof. Finally, due to its dimensional stability, the proposed damping device is not affected by compaction over time and by the consequent increase of the impact force.

Effects of temperature and strain on the resistance to high-rate deformation of copper in shock waves

Elastic–plastic shock compression, unloading, and the stepwise shock compression of copper were investigated at room temperature, 710 °C, and 850 °C to expand the measurement range of high-rate deformations. The dependences of the dynamic yield stress on the temperature and pressure of shock compression were determined from an analysis of the free-surface velocity histories. Although the initial resistance to high-rate deformation increases anomalously with increasing temperature, even a small strain in the shock wave can change the sign of the temperature dependence of the flow stress. Using these data, the dependence of the plastic strain rate on the shear stress in shock waves and temperature was obtained in the range 105–107 s−1. It was found that at room temperature, the ratio between the shear stress and the plastic shear strain rate in a shock wave practically does not depend on the loading history, whereas at 850 °C, the parameters of the plastic flow in the second shock wave deviates significantly from the initial dependence for lower stresses and higher strain rates.

Study of the microstructure and mechanical properties of Al-Si-Fe with additions of chromium by suction casting

The effect of Cr additions on the Al-20Si-5Fe alloy, produced by means of two different solidification methods is presented and discussed. The modification of iron intermetallics and the microstructural refinement through suction casting were also assessed. Several Al−20Si−5Fe−xCr (x = 1.0, 3.0 and 5.0 wt%) alloy ingots were prepared by arc melting furnace (AMF). Rods of each alloy were produced by copper mold suction casting under Ar atmosphere. The elemental chemical analysis was performed by X-ray fluorescence spectrometry (XRF). The microstructure of all samples was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microstructural analysis revealed the presence of α−Al, eutectic silicon (SiE), primary silicon (SiP), Al3FeSi2 and Al95Fe4Cr phases. The microhardness and compressive properties were measured in order to correlate the microstructural changes with Cr additions. The acicular Al3FeSi2 intermetallic compound (2D) obtained by conventional solidification was found to be a plate-like structure (3D). The highest microhardness value was found for the alloys with the 5 wt% Cr (220 HV) in conventional solidification. However, for suction casting, the highest microhardness was 192 HV for the 3 wt% Cr. Although the microhardness dropped with the suction casting, the compressive plasticity of the alloy did increase considerably (>300%), being the microstructural homogeneity the main contributor to the ductility behavior.

The plasticity, crystallization and micro-hardness of Zr–Co–Al-(Nb) BMGs upon rapid quenching and conventional annealing

The GFA and formation of primary B2–ZrCo phase in as-quenched Zr–Co–Al glassy alloys are generally mutually exclusive similar as the attainment of the strength and toughness (damage tolerant) for structural materials. Due to the detrimental effect of high Al content on the B2–ZrCo phase formation, some measures have to be taken to reduce this bad influence. Because the addition of transition elements such as Nb and Co could enhance formation of the B2–ZrCu phase in as-cast ZrCu-based BMG composites, the transition metal of Nb was selected and added to the Zr56Co28Al16 glassy alloy. In this study, the compressive plasticity and activation energies for as-cast Zr–Cu–Al-(Nb) were discussed. Furthermore, the conventional annealing was applied to investigate the effect of Nb on crystallization process because the conventional annealing can be regarded as a precursor to design the Zr–Co–Al BMG composites. The micro-hardness of as-annealed Zr–Co–Al-(Nb) alloys at different annealing temperature and dwelling time has also been studied. This method provides a potential route to stimulate formation of the B2–ZrCo phase without sacrificing the GFA of Zr–Co–Al BMGs.

A novel Fe-Co-Ni-Si high entropy alloy with high yield strength, saturated magnetization and Curie temperature

A novel Fe40Co40Ni10Si10 high entropy alloy (HEA) was designed and fabricated via copper mold casting. It is found that, this alloy is mainly composed of fine lamella-like BCC phase, as well as minor droplet-like FCC phase. This HEA exhibits excellent yield strength of ~1.1 GPa, compressive plasticity of ~38.3%, saturated magnetization of 172 emu/g and Curie temperature of 1169 K, which has significant improvement compared to those of the reported ferromagnetic HEAs, indicating good comprehensive performance combining excellent mechanical and magnetic properties. This study proposes a new approach for the design of high-performance HEAs for functional applications.

Homogenized pouch cell material modelling and a comparison study

Simulation of the mechanical response of lithium-ion battery cells is preferably over experimental due to the explosive nature of them. There are several mechanical modelling methods for representing pouch cells; this study introduces a modified homogenized model. The model uses mechanical responses of layers from literature to establish an average behavior of a pouch cell. Data is normalized, then unified tension and compression stress-strain curves are gathered. These properties are used to build a homogenized pouch cell model by using a tension and compression plasticity model. A stress state dependent failure model (GISSMO) is utilized to demonstrate the damage of cell. Finally, experimental studies from literature are employed for validation. As a result, the model simulates peak forces of all experimental studies with a very low deviation. Homogenizing pouch cell with the proposed approach eliminates modeling detail without compromising the overall mechanical response of the cell. The model is seen to be suitable for applications that do not require a precise mechanical response, such as a battery module or pack analysis.

Intermediate temperature ductility under uniaxial compression in a bulk metallic glass

Quasi-static compression tests were conducted on a Zr-based bulk metallic glass in a temperature ranges from 77 K to 370 K. It is observed that the compressive plasticity presents a maximum value at 273 K, which is about 0.4Tg of the BMG. This is different from usually reported better compressive plasticity under lower ambient temperature. The free volume assisted activation of shear transformation zones and the thermal conduction between shear layer and the rest of the specimen are validated to be suitable to rationalize these observations.

Improvement the Plasticity via Dual-Amorphous and Nanocrystals Synergistically in a Zr-Cu-Al-Nb Bulk Metallic Glass Composite

In this work, a small amount of Nb has been added in a Zr52Cu42.5Al5.5 bulk metallic glass, and a Zr52Cu42Al5.5Nb0.5 bulk metallic glass composite with dual-amorphous and nanocrystal structures has been developed for the first time. This in situ formed bulk metallic glass composite has a larger room compressive plasticity of above 13% than that of the Zr52Cu42.5Al5.5 bulk metallic glass. The excellent plasticity of the bulk metallic glass composite is attributed to the phase-separated matrix with micro-nanocrystal and the nanocrystallization during the deforming process. This work may give a new sight into design bulk metallic glass composites and the underlying mechanism for deformation.

An Electrical Resistivity Method of Characterizing Hydromechanical and Structural Properties of Compacted Loess During Constant Rate of Strain Compression.

Hydromechanical and structural properties of compacted loess have a significant impact on the stability and reliability of subbase and subgrade, which needs to be quickly determined in the field and laboratory. Hence, an electrical resistivity method was used to characterize the hydromechanical and structural properties of compacted loess during constant rate of strain compression. In the present work, compacted loess samples with a dry density of 1.7 g/cm3, a diameter of 64 mm, a height of 10 mm and different water content ranging from 5–25% were prepared. The constant rate of strain (CRS) tests were conducted by a developed oedometer cell equipped with a pair of horizontal circular electrodes (diameter of 20 mm) and vertical rectangular electrodes (width of 3.5 mm) to determine the electrical resistivity of compacted loess. The results showed that as average water content increases, plastic compression indices increase from 0.220 to 0.350 and the elastic compression indices increase from 0.0152 to 0.030, but they decrease to 0.167 and 0.010 and yield stress decreases from 381.28 kPa to 72.35 kPa. Moreover, as vertical strain increases, the variation trend of average formation factor and average shape factor for the lower water content decreases but increases for the maximum water content, and the anisotropy index first decrease and then tend to increase slightly, which indicates that the structural properties of unsaturated and saturated samples during compression exhibits different trend and the anisotropy of samples tend to be stable as vertical strain increases. As the water content increases, the average formation factor and average shape factor decrease, but the anisotropy index first decreases then increases, suggesting that water content has a significant impact on these electrical indices. More important, The coefficients of average formation factor decrease from 33.830 to −1.698 and the coefficients of average shape factor decrease from 8.339 to −0.398 as water content increases, whereas there is less variation for the coefficient of anisotropic index with a value of 2.190. An equation correlating average formation factor and water content and vertical strain is regressed to characterize the hydromechanical properties of compacted loess by measuring its impedance, which can be used to evaluate the stability of compacted loessic ground and subgrade.

Strength and plasticity of amorphous ceramics with self-patterned nano-heterogeneities

Amorphous ceramics with superb strength and irradiation tolerance are promising candidate materials for nuclear industry. However, the brittle-like behavior extremely limits their applications. Here, we demonstrate that Fe–SiOC amorphous ceramic composites (ACCs) with self-patterned Fe-rich nanoclusters fabricated by co-sputtering Fe and amorphous SiOC ceramic not only exhibits exceptional, homogeneous plasticity at room temperature but also remains high strength and good irradiation tolerance. Flow strength of Fe–SiOC ACCs decreases but plasticity increases with the increase in Fe content. Moreover, the strength and plasticity of Fe–SiOC ACCs can be further tailored by subsequent annealing and ion irradiation associated with the change in their microstructure. High temperature annealing tunes amorphous Fe-rich nanoclusters into crystalline Fe nanoparticles, significantly enhancing flow strength of Fe–SiOC ACCs without loss of plasticity. Ion irradiation does not apparently modify the microstructure and reduce plasticity of Fe34at.%-SiOC ACC, but slightly enhances their flow stress. For instance, annealed Fe34at.%-SiOC ACC has flow true stress exceeding 4.0 GPa at a large uniform compressive strain of 55% without plastic flow instability and cracking. The spatially distributed Fe-rich heterogeneities (amorphous nanoclusters and crystalline nanoparticles) plastically co-deform with amorphous SiOC matrix and discretize shear transformation zones in amorphous ceramics, thus preventing the shear-banding instability and significantly enhancing compressive plasticity. The plastic co-deformation between Fe-rich nano-heterogeneities and amorphous SiOC ceramic matrix is achieved due to interface constraint, preventing cracking and ensuring homogeneous plastic deformation of Fe–SiOC ACCs. These findings suggest that patterning nanoscale metal-rich heterogeneities can tailor mechanical properties of amorphous ceramics.

Atomic structure of Co92−xBxTa8 glassy alloys studied by ab initio molecular dynamics simulations

AbstractThe ab initio molecular dynamics simulations were adopted to study the atomic structures of Co92−xBxTa8 (x = 30, 32.5, 35, 37.5, at%) glassy alloys. The results showed that the local packing of B‐centered clusters was more efficient than that of Co‐ and Ta‐centered clusters. It was also found that B‐centered clusters were the primary structure‐forming clusters. The Kasper polyhedra with a Voronoi index of <0 3 6 0> and <0 2 8 0> are dominant in B‐centered clusters. The <0 3 6 0> clusters could especially be formed into a robust network structure, which plays a key role in the increase of mechanical properties. Such a network structure has a higher activation barrier for structural rearrangement and a larger resistance to plastic flow. Thus, the increase in the fraction of <0 3 6 0> with B content would result in an increase in yield strength, as well as a sharp decrease in compressive plasticity.

A combinatorial approach for spinal cord injury repair using multifunctional collagen-based matrices: development, characterization and impact on cell adhesion and axonal growth

Spinal cord injury is a devastating condition of the central nervous system, in which traditional treatments are largely ineffective due to the complex nature of the injured tissue. Therefore, biomaterial-based systems have been developed as possible alternative strategies to repair the damaged tissue. In the present study, we aimed to design bioactive agent loaded scaffolds composed of two layers with distinct physical properties to improve tissue regeneration. An electrospun layer with aligned nanofibers was made of collagen (Col) Type-I, poly(lactide-co-glycolide) (PLGA) and laminin to promote cell attachment of mesenchymal-like stem cells towards the direction of fibers, while a Col-based second layer was fabricated by plastic compression to act as a releasing system for NT-3 and chondroitinase ABC, so that axonal growth could be stimulated. Results showed that a source of mesenchymal stem cell (MSC)-like cells, adipose tissue-derived stem cells cultured on the fibrous layer of the matrices were able to adhere and proliferate, where the aligned fibers promoted the cell growth in an organized way. Furthermore, the bilayered matrices also promoted dorsal root ganglion neurite outgrowth. The bilayered matrice with Col/PLGA + laminin top layer appears to promote higher neurite growth. Collectively, the designed constructs show promising structural properties and biological performance for being employed as a scaffold for engineering the spinal cord tissue.

SCOPE OF IMPROVING MECHANICAL CHARACTERISTICS OF CONCRETE USING NATURAL FIBER AS A REINFORCING MATERIAL

Using natural (Jute) fiber in concrete as a reinforcing material can not only augment the concrete strength but also restrict the use of synthetic fiber which is environmentally detrimental. To achieve this goal, this study evaluated compressive strength, tensile strength and plastic shrinkage of concrete incorporating ‘Natural (Jute)’ fiber of different length (15 mm and 25 mm) with various mix proportions of 0.10%, 0.2%, 0.3% and 0.4% respectively by volume of concrete. Concrete is vulnerable to grow shrinkage cracks because of high evaporation rate in dry and windy conditions. Incorporating of fibers could abate development of this crack. The large length (25 mm) and higher content ( 0.3%) of reinforcing materials (jute fiber) result to the lowering of mechanical properties of JFRC compare to plain concrete. But in the incorporation of short (15 mm) and low fiber content ( 0.3%), enhances the mechanical properties of the same JFRC. Inclusion of 0.3% (15 mm length) fiber gave maximum enhancement of both concrete compressive and tensile strength by 12.4% and 58% respectively compared to the non-fiber reinforced concrete. A drastic suppression of crack occurrence and area of crack between non-fiber reinforced concrete and fiber reinforced concretes was attained. Experimental results of incorporating 0.1–0.4% fiber with 15 mm length in concrete revealed that plastic shrinkage cracks were decreased by 75–99% in contrast to non-fiber reinforced concrete. Therefore, it is concluded that the incorporation of jute fiber in making FRC composite would be one of the favorable methods to enhance the performance of concrete.

SCOPE OF IMPROVING MECHANICAL CHARACTERISTICS OF CONCRETE USING NATURAL FIBER AS A REINFORCING MATERIAL

Using natural (Jute) fiber in concrete as a reinforcing material can not only augment the concrete strength but also restrict the use of synthetic fiber which is environmentally detrimental. To achieve this goal, this study evaluated compressive strength, tensile strength and plastic shrinkage of concrete incorporating ‘Natural (Jute)’ fiber of different length (15 mm and 25 mm) with various mix proportions of 0.10%, 0.2%, 0.3% and 0.4% respectively by volume of concrete. Concrete is vulnerable to grow shrinkage cracks because of high evaporation rate in dry and windy conditions. Incorporating of fibers could abate development of this crack. The large length (25 mm) and higher content ( 0.3%) of reinforcing materials (jute fiber) result to the lowering of mechanical properties of JFRC compare to plain concrete. But in the incorporation of short (15 mm) and low fiber content ( 0.3%), enhances the mechanical properties of the same JFRC. Inclusion of 0.3% (15 mm length) fiber gave maximum enhancement of both concrete compressive and tensile strength by 12.4% and 58% respectively compared to the non-fiber reinforced concrete. A drastic suppression of crack occurrence and area of crack between non-fiber reinforced concrete and fiber reinforced concretes was attained. Experimental results of incorporating 0.1–0.4% fiber with 15 mm length in concrete revealed that plastic shrinkage cracks were decreased by 75–99% in contrast to non-fiber reinforced concrete. Therefore, it is concluded that the incorporation of jute fiber in making FRC composite would be one of the favorable methods to enhance the performance of concrete.

Experimental study on ultra-high performance concrete under triaxial compression

Ultra-high strength concrete (UHSC) and Ultra-high performance concrete (UHPC) with high compressive strength and good durability have been increasingly used in engineering structures. In the present study, uniaxial and triaxial compression tests on UHSC and UHPC are carried out by using servo-hydraulic actuators to investigate the mechanical properties of UHSC and UHPC under various stress states. In triaxial compression tests, the confining pressure ranging from 0 to 50 MPa is applied on UHSC and UHPC specimens. The mechanical responses of UHSC and UHPC specimens under various confining pressures, including peak strength, axial and circumferential strain are recorded in the loading process. According to the elastoplastic behavior of UHSC and UHPC specimens in tests, the influence of confining pressure on the compressive strength and plastic deformation performances of UHSC and UHPC are studied. It is found that the compressive strength and plastic deformation capacity of UHSC and UHPC tend to be higher with the increasing of confining pressure. The enhancement of compressive strength of UHPC is slightly lower than that of UHSC However, due to the lateral restraint effect of the confining pressure and the tensile action of the steel fibers inside the UHPC specimen, failure of the cylindrical specimen are delayed more significantly with increasing of confining pressure. Failure surfaces based on Ottosen’s criterion for UHSC and UHPC are identified accroding to test data. By comparing and analyzing the tests results on UHSC, UHPC and previously tested C200, it is concluded the effect of confining pressure on the enhancement of compressive strength of concretes has a negative relationship with the uniaxial compressive strength of concretes.

Effects of Cu content on crystallization behavior, mechanical and soft magnetic properties of Fe80-xCuxP13C7 bulk metallic glasses

Bulk Fe80-xCuxP13C7 (x = 0, 0.1, 0.3 and 0.6 at.%) amorphous alloys were successfully fabricated utilizing the combining fluxing treatment and J-quenching technique. The influence of Cu content on the crystallization characteristic temperatures and primary crystallization phase evolution, glass formation ability, mechanical and soft magnetic properties of Fe-Cu-C-P BMGs have been systematically investigated. Additionally, the proper addition of Cu content can significantly improve the compression plasticity of present Fe-Cu-C-P bulk glassy alloys, and the Fe79.4Cu0.6P13C7 bulk glassy rod exhibits an excellent plasticity of 5% as well as a high fracture strength (over 2700 MPa). Then, the multiple effects of annealed Fe80-xCuxP13C7 BMGs on mechanical properties and soft magnetic property have been investigated. More importantly, Fe79.4Cu0.6P13C7 BMG annealed at Tg-30 K for half an hour exhibits excellent soft magnetic properties with relatively high saturation magnetization of 1.5 T, and mechanical properties with the fracture strength of 3280 MPa and plastic strain of 4%.

A New Model for Calculation of the Plastic Compression Index and Porosity and Permeability of Gob Materials in Longwall Mining

In coal longwall mining the accuracy of gob methane drainage system design, control of methane leakage into the longwall stope, and control of spontaneous combustion potential all depend on the porosity and permeability of the gob material. However, longwall mining conditions do not allow for any direct measurements of the gob material characteristics. Therefore, the simulation of gob material as a granular medium contributes to the ability to predict gob porosity. Many features of a granular medium, like gob material, are directly and indirectly affected by its particle size distribution. Fractal models are commonly used for porosity prediction which allows for a better understanding of how porosity can change with stress states based on the fragmentation size distribution of gob material. The plastic compression index (PCI), which describes the degree of compression of the broken material in gob, can be calculated using the physical properties of the broken material. However, using the existing fractal models, it is difficult to determine this parameter because of the multiplicity of parameters. In this research, a new fractal model was developed to facilitate the calculation of the PCI parameter and to increase the accuracy and validity of the results. Using data from the Tabas coal mine, the porosity-stress and permeability-stress curves were investigated for the gob material. The porosity results from this study agreed with those of Fan's gob compression model in a comparison. Although the obtained permeability results were within the range of previous studies, Berg's permeability model provided a better tool for estimation of the gob permeability.

Modification of Surface of Carbon Fiber Materials by Plasma Treatment (Review)

Modern processes for plasma modification of carbon fiber materials with the aim of improving the degree of adhesive interaction at the boundary between the polymeric matrix and the carbon reinforcing filler are reviewed. The strength of adhesion of carbon fibers to the polymeric matrix at the interface has a deciding effect on the strength of the carbon plastics in shear and compression and determines to a significant degree the crack resistance of the carbon plastic materials, the specific impact viscosity, and the dynamic fatigue resistance, thereby determining the durability of constructions made from them.