Catastrophic Brittle Fracture Research Articles

Progressive damage and tensile failure of open‐hole carbon fiber polymer composites reinforced by carbon nanotubes

AbstractProgressive damage and tensile failure of open‐hole carbon fiber/carbon nanotube reinforced composites with different off‐axis angles were detected by acoustic emission and Micro‐CT. K‐mean clustering algorithm can be utilized to post‐process signals of acoustic emission. Three critical points including linear growth point, near maximum load point and failure point, were selected to study progressive damage. Results indicated that stiffness variable decreased with the increase of off‐axis angle. When the off‐axis angle was 0°, higher initial stress and catastrophic brittle fracture characteristics can be obtained, whereas pseudo‐ductile behavior can be observed when off‐axis angles were 30° and 45° because of the alignment of yarn (fiber trellising) and the matrix plasticity. Due to the symmetrical structure of plain texture, there was a very interesting phenomenon that the tensile strength of composite specimen with 45° off‐axis angle was 23.65% higher than that of the specimen with an off‐axis angle of 30°. In the second stage of loading, the slope drop sharply when the load reached first key point, and Kaiser Effect can be observed. Acoustic emission technology and Micro‐CT method are beneficial to damage assessment of complex composites.

Extreme dislocation-mediated plasticity of yttria-stabilized zirconia

Ceramics constitute a major class of engineering materials, but their applications are severely undercut by the propensity to catastrophic brittle fracture. Due to the brittleness and sensitivity to flaws, dislocation-mediated plasticity is rarely achieved in ceramics at room temperature. Here, we report in-situ mechanical testing on oriented submicron single-crystal pillars of cubic yttria-stabilized zirconia (YSZ) in the transmission electron microscope, to show that ultra-large plastic deformation mediated by dislocations can be achieved at room temperature. By employing three-dimensional tomography and atomic imaging, unprecedented details of spatial features of the generated dislocations are demonstrated. While deformation in pillars compressed along <111> directions is achieved by dislocation slip on the non-close-packed {001} planes, strains in those compressed along <001> are by slip on the close-packed {111} planes. Different dislocation slips cause obvious anisotropy in mechanical properties of YSZ crystal. The <111> pillars exhibit much greater plastic deformability than the <001> pillars, with observed strains as high as 61.6%. These results may lead to potentially new applications of YSZ at submicron scales and provide important insights into deformation mechanisms of ionic ceramics in general.

Synthesis of coatings on SiC fibers and their effects on microstructure and mechanical properties of SiCf/SiBCN composites

AbstractIn this study, the amorphous C, ZrB2, and BN single‐layer coatings as well as C/BN, C/ZrB2, ZrB2/BN, and C/ZrB2/BN composite coatings were prepared on SiC fibers (SiCf) by an in situ synthesis and solution impregnation–pyrolysis method. Subsequently, SiCf/SiBCN composites were fabricated by hot‐pressing sintering at 1900℃/60 MPa/30 min to explore the influence of different coatings on the microstructure and mechanical performance of resulting composites. After the preparation of single‐layer‐coated SiCf, the SiCf(BN) or SiCf(ZrB2) tended to be overlapped with each other, whereas the dispersion of amorphous C–coated SiCf was satisfying. Besides, some uneven areas and attached particles have appeared on fiber surfaces of the SiCf(BN) or SiCf(ZrB2), whereas smooth and dense surfaces of amorphous C–coated SiCf were observed. Because the uniformity of ZrB2 coatings can be partially damaged by the subsequent coating process of BN, the composite coatings of ZrB2/BN and C/ZrB2/BN were thereby not suitable for strengthening SiBCN matrix. The SiCf/SiBCN composites with C/ZrB2 coatings have desirable comprehensive mechanical properties. Nevertheless, the conventional toughening mechanisms such as fiber pull‐out and bridging, and crack deflection are not available for these composites because the serious crystallization of SiCf leading to great strength loss, resulting in catastrophic brittle fracture.

Research Progress on Corrosion Resistance of Titanium Alloy Oil Well Tubing

Compared with aluminum alloy and alloy steel, titanium alloy has higher specific strength, lower modulus of elasticity, and better toughness, fatigue performance and corrosion resistance. In terms of oil well tubing, the development of titanium alloy lags behind that of aluminum alloy and alloy steel. Aluminum alloy tubing is sensitive to pitting, fatigue corrosion and stress corrosion cracking. At the same time, it is not suitable for ultra-deep wells due to temperature limitations. Easily interact with corrosive media to cause corrosion and cracking. Titanium alloy oil well tubing is expected to solve this corrosion problem, but its corrosion resistance research is still incomplete. Therefore, it is necessary to develop titanium alloy oil well tubing with good corrosion resistance to improve corrosion fatigue (CF), fatigue during deep oil well and natural gas drilling operations. Catastrophic brittle fracture caused by hydrogen induced cracking (HIC), pitting corrosion and sulfide stress cracking (SSC). In this paper, by investigating a large number of domestic and foreign documents, the corrosion types of titanium alloy oil well pipes are analyzed, and the research status of corrosion resistance of titanium alloy oil well pipes is reviewed from three aspects: oil pipes, casings and drill pipes.

Room-temperature plasticity in diamond

In spite of extremely high strength and hardness, the property of brittleness is tightly linked to diamond. In the deformation of diamond at room temperature, the plasticity of the diamond is normally considered hard to occur because of the domination of catastrophic brittle fracture. Herein, we employed in-situ transmission electron microscopy to reveal the diamond room-temperature plastic behavior, and compared it with a recent report (Adv. Mater. 2020, 1906458) on transformation-induced room-temperature plasticity of diamond nanopillars. Our present in-situ uniaxial compression tests in sub-micron-sized diamond pillars indicate that the plasticity in diamond is carried out by dislocations slipping instead of phase transformation and the initiation of plasticity highly depends on the stress state. On the other hand, we noted that a high proportion of amorphous surface layer in the diamond pillars with a diameter of less than 20 nm may be a significant factor leading to the plasticity.

Direct Observation of Room-Temperature Dislocation Plasticity in Diamond

It is well known that diamond does not deform plastically at room temperature and usually fails in catastrophic brittle fracture. Here we demonstrate room-temperature dislocation plasticity in sub-micrometer sized diamond pillars by in-situ mechanical testing in the transmission electron microscope. We document in unprecedented details of spatio-temporal features of the dislocations introduced by the confinement-free compression, including dislocation generation and propagation. Atom-resolved observations with tomographic reconstructions show unequivocally that mixed-type dislocations with Burgers vectors of 1/2<110> are activated in the non-close-packed {001} planes of diamond under uniaxial compression of <111> and <110> directions, respectively, while being activated in the {111} planes under the <100> directional loading, indicating orientation-dependent dislocation plasticity. These results provide new insights into the mechanical behavior of diamond and stimulate reconsideration of the basic deformation mechanism in diamond as well as in other brittle covalent crystals at low temperatures.

A Materials Perspective on the Design of Damage-Resilient Bone Implants Through Additive/Advanced Manufacturing

After more than 5 decades of research, the failure of bone implants is still poorly understood. The aging population makes it increasingly urgent to solve this issue. Among the reasons for failure, catastrophic brittle fracture can be directly related to the implant material and fabrication and deserves more attention. Indeed, clinically available implants do not sufficiently reproduce the hierarchical and heterogeneous microstructural organization of our natural bones, ultimately failing at replicating their mechanical strength and toughness. Nevertheless, recent advances in additive and advanced manufacturing have opened new horizons for the fabrication of biomimetic bone implants, challenging at the same time their characterization, testing, and modeling. This critical review covers selected recent achievements in bone implant research from a materials standpoint and aims at deciphering some of the most urgent issues in this multidisciplinary field.

The effect of unit cell size and topology on tensile failure behavior of 2D lattice structures

In this paper, a theoretical model is proposed to predict the initial failure location and the failure progression of the lattice structures made from the elastic-brittle bulk materials. The effects of size and topology on the tensile failure behavior of multiple representative lattice structures (2D auxetic, 2D diamond, 2D triangular1 and 2D triangular2), under various geometry design conditions (including cell topology, cell size and number of unit cells), are systematically investigated through the proposed analytical model. From the results, it was shown that the 2D bending-dominated structures with lower nodal connectivity (number of struts that meet in joints) (2D auxetic and 2D diamond) exhibited a relatively progressive crack propagation pattern, while the 2D stretching-dominated structures with higher nodal connectivity (2D triangular1 and 2D triangular2) appear to exhibit rather catastrophic brittle fracture failure. During the failure fracture propagation, the energy absorption of the 2D stretching-dominated structures were significantly higher than that of the 2D bending-dominated structures. Moreover, for all lattice designs, the tensile failure behaviors tend to converge to more consistent patterns when the unit cell numbers increase beyond certain limitations.

Pseudo-ductile fracture of 3D printed alumina triply periodic minimal surface structures

Additive manufacturing enables the fabrication of periodic ceramic lattices with controllable micro-architectures. Many studies reported their catastrophic brittle fracture behaviour. However, ceramic lattices may fail by a layer-by-layer pseudo-ductile fracture mode, by controlling micro-architectures and porosities. Moreover, their fracture behaviour can be optimised by introducing strut/wall thickness gradients. This paper investigates the fracture behaviour and the fracture mode transition of ceramic triply periodic minimal surface (TPMS) structures. Alumina TPMS structures with relative densities of 0.14-0.37 are fabricated by ceramic stereolithography. Quasi-static compression tests validate a transition density range for non-graded samples: low (<0.21) and moderate (>0.25) relative density samples show layer-by-layer pseudo-ductile and catastrophic brittle fracture modes, respectively. The pseudo-ductile failure mode increases the energy absorption performance, enabling load-bearing capacity for a compressive strain up to 50%. With appropriate thickness gradients, graded structures exhibit significant increase of energy absorption without a decrease of fracture strength compared to their non-graded counterparts.

Effect of Sm on thermal and mechanical properties of Cu-Zr-Al bulk metallic glasses

The effect of rare-earth (Sm) microalloying on the thermal stability and phase selection along with the effect of nanocrystallization on the mechanical properties of amorphous melt-spun ribbons of Zr50Cu40Al10, Zr49Cu39.2Al9.8Sm2 and Zr48Cu38.4Al9.6Sm4 alloys were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), Vickers and nanoindentation hardness tests and micropillar compression analysis. XRD and TEM analyses showed that all samples were fully amorphous in as-spun state; however, crystallization sequences for the Sm-free and the Sm micro-alloyed samples were different during devitrification. Combined study of XRD, DSC and TEM on melt-spun ribbons show that Zr48Cu38.4Al9.6Sm4 have nanocrystallization of Cu2Sm phase with an average diameter of 10 nm, which was absent in Zr50Cu40Al10, prior to crystallization of Cu10Zr7 phase. The nanoindentation and micropillar compression tests revealed Cu2Sm nanocrystals embedded in Zr48Cu38.4Al9.6Sm4 alloy improves strength and hardness. On the other hand, presence of these nanocrystals deteriorate shear band stability and thus result in a catastrophic brittle fracture through a single shear band burst.

Plastic deformation behavior of a novel Fe-based metallic glass under different mechanical testing techniques

A novel Fe-based metallic glass (Fe0.52Co0.30Ni0.18)73Cr17Zr10 without metalloids has been prepared. Its mechanical properties and plastic deformation behavior have been investigated systematically by bending test, tensile test and Vickers indentation test. This metallic glass ribbon exhibits good bending ductility, but it shows catastrophic brittle fracture in tensile tests. The Vickers hardness is 904.4 HV, which is higher than most of used quenched steel, manifesting the possibility of good wearability. Under different indentation forces, the plastic deformation of indentation is adjusted through radial and semi-circular shear bands. The average indentation size(D) and the radius of plastic deformation zone(R) increases with increasing indentation forces(P). The normalized shear deformation zone(R/D) is unrelated with indentation forces.

Tensile behavior of Cu-coated Pd40Cu30Ni10P20 metallic glassy wire

Catastrophic brittle fracture of monolithic metallic glass (MG) hinders engineering application of MGs. Although many techniques has been tried to enhance tensile ductility of metallic glasses, the enhancement is quite limited. Here, we show the effect of electrodeposited Cu coating on tensile plasticity enhancement of Pd40Cu30Ni10P20 MG wires, with different volume fractions of copper coatings (R), from 0% to 97%. With increasing R, tensile elongation is enhanced to 7.1%. The plasticity enhancement is due to confinement of the Cu coatings, which lead to multiple and secondary shear bands, according to SEM investigations. In addition, the SEM images also show that the patterns on the fracture surface of the Cu-coated MG wires vary with volume fraction of the Cu coatings. The size of shear offset decreases with increasing R. The viscous fingerings on the fracture surface of monolithic MG wire changes into dimples on the fracture surface of Cu coated MG wires with R of 90% and 97%. The electrodeposition technique used in this work provides a useful way to enhance plasticity of monolithic MGs under tensile loading at room temperature.

Design of fracture-resistant silicon structure with molecular dynamics simulation

The inherent brittleness of crystalline silicon is a cause of concern for processing, handling and application of the material. Here a simulation-based design is proposed to reduce the risk of catastrophic brittle fracture of devices and components made of silicon. In this scheme, ultrathin layers of amorphous silicon are introduced within the crystalline silicon to create a multilayered laminated structure. Using molecular dynamics simulations, we demonstrate that in this nanolaminate, a crack growing within the crystalline region gets pinned at the amorphous layers. This phenomenon occurs due to the observed ductility in amorphous silicon, which resembles the shear-band mediated deformation of metallic glasses. Asa consequence, the catastrophic failure is averted by localizing the damage and preventing it from extending across the material.

Analysis of Shear Banding in Zr-Based Metallic Glass under Laser Shock Peening and Bending

Metallic glasses have been expected to be used as structural materials since their high strength and high hardness. Unfortunately, their catastrophic brittle fracture behavior with poor plasticity becomes the major weakness for structural application. It has been recognized that the mechanism of plastic deformation in metallic glasses is through the formation of shear bands, which provide them with limited ductility. Laser shock peening (LSP) is an innovative surface treatment technique which can introduce deep compressive residual stress layer to materials for improving their mechanical behavior. In this work, a finite-element model has been developed to numerically simulate the pure bending process, LSP and subsequent bending process. An advanced constitutive equation was established based on the large deformation theory of nonlinear mechanics, the free volume model and the Coulomb-Mohr yield criterion. The model is able to capture the following results: (i) for a given bending deflection, the shear band spacing increases with increasing plate thickness; (ii) for a given plate thickness, the free volume increases with the bending deflection; (iii) for a given thickness and a given deflection, the shear bands increase under the effect of LSP.

Mechanical Properties of Molybdenum Disulfide and the Effect of Doping: An in Situ TEM Study.

Direct observations on nanopillars composed of molybdenum disulfide (MoS2) and chromium-doped MoS2 and their response to compressive stress have been made. Time-resolved transmission electron microscopy (TEM) during compression of the submicrometer diameter pillars of MoS2- and Cr-doped MoS2 (Cr: 0, 10, and 50 at %) allow the deformation process of the material to be observed and can be directly correlated with mechanical response to applied load. The addition of chromium to the MoS2 changed the failure mode from plastic deformation to catastrophic brittle fracture, an effect that was more pronounced as chromium content increased.

Dynamic bending behaviour of woven composites for sports products: Experiments and damage analysis

Abstract Carbon fabric-reinforced polymer (CFRP) laminates employed in sports products are usually subjected to large-deflection quasi-static and dynamic bending deformations during service. Such loading conditions induce damage within the material affecting its strength, stiffness and energy-absorbing capability. To study this, mechanical behaviour of woven CFRP composites in on- and off-axis orientations is first quantified by carrying out large-deflection quasi-static bending tests followed by dynamic ones employing an Izod type impact tester. CFRP laminates of various orientations were tested at loads increasing up to failure to determine their energy-absorbing capability. On-axis laminates demonstrated better strength and stiffness whereas off-axis laminates exhibited good energy-absorbing capability. However, for applications demanding strength, stiffness and energy absorption as in sports products, a combination of both types of plies, as in a quasi-isotropic layup, is an optimum choice. Micro-computed tomography (micro-CT) analysis of the tested specimens showed that matrix cracking, delamination and tow debonding were the dominant damage modes at the specimen's impact location, whereas fabric fracture occurred at the bending location. Further, a catastrophic brittle fracture was observed in the on-axis laminates whereas the off-axis laminates exhibited pseudo-ductile behaviour thanks to matrix cracking and fibre trellising before their failure at higher energies.

Elimination of strength degrading effects caused by surface microdefect: A prevention achieved by silicon nanotexturing to avoid catastrophic brittle fracture.

The unavoidable occurrence of microdefects in silicon wafers increase the probability of catastrophic fracture of silicon-based devices, thus highlighting the need for a strengthening mechanism to minimize fractures resulting from defects. In this study, a novel mechanism for manufacturing silicon wafers was engineered based on nanoscale reinforcement through surface nanotexturing. Because of nanotexturing, different defect depths synthetically emulated as V-notches, demonstrated a bending strength enhancement by factors of 2.5, 3.2, and 6 for 2-, 7-, and 14-μm-deep V-notches, respectively. A very large increase in the number of fragments observed during silicon fracturing was also indicative of the strengthening effect. Nanotextures surrounding the V-notch reduced the stress concentration factor at the notch tip and saturated as the nanotexture depth approached 1.5 times the V-notch depth. The stress reduction at the V-notch tip measured by micro-Raman spectroscopy revealed that nanotextures reduced the effective depth of the defect. Therefore, the nanotextured samples were able to sustain a larger fracture force. The enhancement in Weibull modulus, along with an increase in bending strength in the nanotextured samples compared to polished single-crystal silicon samples, demonstrated the reliability of the strengthening method. These results suggest that this method may be suitable for industrial implementation.

Analytical and experimental studies on ballistic impact behavior of carbon nanotube dispersed resin

An analytical formulation is presented for the prediction of ballistic impact behavior of multi-walled carbon nanotube (MWCNT) dispersed epoxy resin. The formulation is based on stress wave propagation and energy balance between the projectile and the target. During the ballistic impact event, the energy lost by the projectile is absorbed by the target through various damage and energy absorbing mechanisms such as compression of the target directly below the projectile, compression in the region surrounding the impacted zone, shear plugging, formation of ring and radial cracks in the resin leading to tensile failure and energy absorbed due to the presence of carbon nanotubes. Complete failure of the target was due to catastrophic brittle fracture and shattering. Experimental studies are carried out on ballistic impact behavior of neat epoxy and MWCNT dispersed epoxy. Typical results on ballistic limit velocity and energy absorbed by various mechanisms are presented. Ballistic impact behavior of neat epoxy resin and MWCNT dispersed epoxy resin are compared. A good match is observed between the analytical and experimental results.

Buckling of metallic glass bars

Uniaxial compression tests of slender metallic glass bars of composition Zr52.5Cu17.9Ni14.6Al10Ti5 (at.%) have been conducted. It was found that the Zr-based metallic glass bars have a tendency to buckle elastically or plastically rather than to yield or fracture if its slenderness ratio is over a critical value. The elastic buckling undermines the intrinsic strength of the metallic glass, but the plastic buckling imparts the metallic glass a benign failure mode and avoids the catastrophic brittle fracture. The phenomena are understood by the unique stress state across the bar. The result has implication for the measurement of mechanical properties of bulk metallic glasses and is of significance in the application of metallic glass members in engineering structures.

A critical review of the influence of hydrogen on the mechanical properties of medium-strength steels

AbstractAs medium-strength steels are promising candidates for the hydrogen economy, it is important to understand their interaction with hydrogen. However, there are only a limited number of investigations on the behavior of medium-strength steels in hydrogen. The existing literature indicates that the influences of hydrogen on the tensile properties of medium-strength steels are mainly the following: (i) the steel can be hardened by hydrogen, as demonstrated by an increase in the yield stress or ultimate tensile stress; (ii) some steels can be embrittled by hydrogen, as revealed by lower yield stress or ultimate tensile stress; (iii) in most cases, these steels may experience hydrogen embrittlement (HE), as indicated by a reduction in ductility. The degree of HE mainly depends on the test conditions and the steel. The embrittlement can lead to catastrophic brittle fracture in service. The influence of hydrogen on the fatigue properties of medium-strength steels is dependent on many factors such as the stress ratio, temperature, yield stress of the steel, and test frequency. Generally, the hydrogen influence on fatigue limit is small, whereas hydrogen can accelerate the fatigue crack growth rate, leading to a shorter fatigue life. Inclusions are an important factor influencing the properties of medium-strength steels in the presence of hydrogen. However, it is not possible to predict the influence of hydrogen for any particular steel that has not been experimentally evaluated or to predict service performance. It is not known why similar steels can have different behavior, ranging from good resistance to significant embrittlement. A better understanding of the microstructural characteristics is needed.