Delamination Fracture Research Articles

Ductile ultrastrong China low activation martensitic steel with lamellar grain structure

The low high-temperature mechanical properties of reduced activated ferrite martensitic (RAFM) heat-resistant steels limit the maximum operating temperature of nuclear fusion reactors. However, it is difficult to improve the strength of the material without reducing its plasticity. In this study we prepared a China low activation martensitic (CLAM) steel with a layered structure through hot rolling followed by low-temperature tempering, which successfully improved its strength and ductility. In addition, we elucidate the ductility mechanisms in such lamellar structural materials. When the strength of the grain boundaries exceeds that of the grains, cracks will continuously extend along the layered grain boundaries, eventually resulting in a delamination fracture mechanism. When the grain strength exceeds that of the grain boundaries, cracks will continuously form through the relative sliding of the grain boundaries, and a large number of small cracks will initiate and propagate longitudinally along the layered boundaries. Both forms of crack propagation cause longitudinal expansion along the layered grain boundaries. The resulting longitudinal extension of cracks markedly diminishes local stress concentration to promote plastic deformation, thereby significantly increasing the ductility of the material. Employing the combination of this delamination ductility mechanism with interface strengthening and precipitation strengthening, the strength of the CLAM steel for nuclear applications is shown to be enhanced by ∼30 % without loss of elongation. The current delamination ductility strategy provides a unique pathway to develop materials with ultrahigh strength and superior ductility at economical material costs.

A critical review on fractographic studies of steel cord and bead wire used in tyre reinforcement

Fracture is one of the failure modes of a material or product which may occur during its manufacturing process or its usage. Fractography is the science and art of examination and analysis of the fractured surface. Texture and nature of the fractured surface provide valuable information on origin of a crack and crack propagation; thereby, it helps to understand the mechanism of fracture and facilitate to identify the likely causes of failure. This review covers an extensive study on various types of fractures of steel cord and bead wire which are primarily used in rubber composites viz tyre, conveyor belt etc. Different types of fractures studied include ductile, central burst, brittle, fatigue, torsion, corrosion, delamination and weld fractures. Fundamentals on specific characteristics of each type of fracture and their likely causes have been elaborately discussed Microscopic examination through scanning electron microscope (SEM) provides deeper insights of the fractured surface as well as microstructure of material. In addition to the fundamental aspects of fractures, examples of different types of fractured samples have been illustrated in this article. This focused review would be useful to the steel cord and bead wire manufactures as well as to tyre manufacturers for detailed failure investigation of material/product and thereby to take appropriate corrective measures.

Tailoring layered Csf/SiBCN composites with pseudoplastic fracture behavior: Strengthening and toughening mechanisms

AbstractThe layering process using phenolic resin coupled with pressureless sintering technique was explored to prepare short carbon fiber‐reinforced SiBCN composites (Csf/SiBCN). The effect of phenolic resin content on the microstructure and mechanical properties of Csf/SiBCN was mainly studied. Results suggest that the addition of phenolic resin can appropriately improve density and flexural strength and reduce total pore volume of the composites because phenolic resin can partly consolidate SiBCN powders to promote shaping via low‐temperature pressureless sintering. As the phenolic resin content increases, the fracture behavior changes from delamination fracture to monolithic fracture, thereby reducing fracture displacement. The reason for this performance is that the interlayer bonding is enhanced to hinder crack propagation along the layers.

Ballistic response and failure mechanisms of gradient structured Mg alloy

Due to their low density, high specific damping capacity and high shock absorbency, magnesium (Mg) alloys have great potential for development as high-performance lightweight armor materials in industrial applications. However, their applications are still limited owing to low strength, ductility and formability. Gradient structure design has been shown to be a good method for improving the mechanical properties and ballistic resistance of Mg alloy plate. This work aims to thoroughly reveal the root causes of ballistic performance enhancement of gradient structured (GS) Mg alloy armor material through ballistic tests and finite element simulations. Compared with homogeneous Mg alloy plate of the same dimensions, the impact energy absorption of GS plate is increased by about 40%. The enhanced strength and plasticity from the gradient structure design certainly contribute in part to the ballistic resistance. More importantly, the gradient structure results in a transition of failure modes from the typical petal-shaped dehiscence to delamination and shear fracture. Based on detailed finite element analysis, we deeply understand the deformation process and the effect of the gradient structure on the propagation of stress wave during ballistic impacting. The energy absorption by each defeat mechanism is also theoretically calculated to quantitatively interpret their intrinsic effects. Meanwhile, microstructural observations and fracture morphology have demonstrated the appearance of adiabatic shear bands along the boundary of the cylindrical plunger after ballistic perforation of GS plate. Therefore, the failure mode transition caused by gradient structure design must also play a major role in improving the ballistic resistance.

Ballistic Behavior of Epoxy Composites Reinforced with Amazon Titica Vine Fibers (Heteropsis flexuosa) in Multilayered Armor System and as Stand-Alone Target.

Seeking to improve personal armor equipment by providing mobility and resistance to penetration, this research aimed to explore the potential of sustainable materials in order to assess their ability in ballistic applications. Titica vine fibers (TVFs) extracted from aerial roots of Heteropsis flexuosa from the Amazon region were incorporated at 10, 20, 30, and 40 vol% into an epoxy matrix for applications in ballistic multilayered armor systems (MASs) and stand-alone tests for personal protection against high-velocity 7.62 mm ammunition. The back-face signature (BFS) depth measured for composites with 20 and 40 vol% TVFs used as an intermediate layer in MASs was 25.6 and 32.5 mm, respectively, and below the maximum limit of 44 mm set by the international standard. Fracture mechanisms found by scanning electron microscopy (SEM) attested the relevance of increasing the fiber content for applications in MASs. The results of stand-alone tests showed that the control (0 vol%) and samples with 20 vol% TVFs absorbed the highest impact energy (Eabs) (212-176 J), and consequently displayed limit velocity (VL) values (213-194 m/s), when compared with 40 vol% fiber composites. However, the macroscopic evaluation found that, referring to the control samples, the plain epoxy shattered completely. In addition, for 10 and 20 vol% TVFs, the composites were fragmented or exhibited delamination fractures, which compromised their physical integrity. On the other hand, composites with 30 and 40 vol% TVFs, whose Eabs and VL varied between 166-130 J and 189-167 m/s, respectively, showed the best physical stability. The SEM images indicated that for composites with 10 and 20 vol% TVFs, the fracture mode was predominantly brittle due to the greater participation of the epoxy resin and the discrete action of the fibers, while for composites with 30 and 40 vol% TVFs, there was activation of more complex mechanisms such as pullout, shearing, and fiber rupture. These results indicate that the TVF composite has great potential for use in bulletproof vests.

Investigation of crack propagation in filament wound composite samples of Mode-I by using acoustic emission technique

A common industrial method of fabricating composite structural is filament winding, which is widely used to manufacture axisymmetric components. One of the most prevalent damage mechanisms in these composite structures is delamination, which occurs in various types of loading. In this research, the mechanical behavior and propagation of the initial crack of Mode-I in carbon/epoxy filament wound (FW) composite curve beams have been investigated via the acoustic emission (AE) method. For this purpose, at first, a composite tube was made with considering the artificial interlayer separation, and the beam specimens were cut from the longitudinal direction. At first, the initiation of the failures was determined using the AE method. Then, the growth and spread of interlayer delamination were investigated by the energy of AE signals and the sentry function. By determining the speed of the AE waves and providing a method to filter unwanted signals, the momentary position of the interlayer delamination tip during growth is predicted. The results showed that the fiber bridging phenomenon was due to the penetration of the two regions adjacent of the separation interface, and the fiber bridging length considerably affected the Mode-I delamination fracture toughness. In addition, the fracture toughness increased as the fiber bridging zone enlarged. Finally, good agreement was observed between the fracture toughness values obtained from the AE method and those found in the standard ASTM D5528.

Experimental and Numerical Investigation of the Tensile and Failure Response of Multiple-Hole-Fiber-Reinforced Magnesium Alloy Laminates under Various Temperature Environments.

In this paper, the tensile mechanical behavior and progressive damage morphology of glass-fiber-reinforced magnesium alloy laminate for different numbers of holes in a temperature range of 25-180 °C were investigated. In addition, based on extensive tensile tests, the tensile mechanical behavior and microscopic damage morphology of porous-glass-fiber-reinforced magnesium alloy laminates at different temperatures were observed by finite element simulation and scanning electron microscopy (SEM). Finally, the numerical simulation and experimental results were in good accordance with the prediction of mechanical properties and fracture damage patterns of the laminates, the average difference between the residual strength values of the specimens at ambient temperature was 5.57%, and the stress-strain curves were in good agreement. The experimental and finite element analysis results showed that the damaged area of the bonded layer tended to expand with the increase in the number of holes, which has a lesser effect on the ultimate tensile strength. As the temperature increased, the specimens changed from obvious fiber breakage (pull-out) and the resin matrix damage mode to matrix softening damage and interfacial delamination fracture damage. As the testing temperature of the specimens increased from 25 °C to 180 °C, the tensile strength of the specimens decreased by an average of 51.59%, while the tensile strength of the specimens showed a nonlinear decreasing trend. The damage mechanism of porous-glass-fiber-reinforced magnesium alloy laminates at different temperatures is discussed in this paper, which can provide a reference for engineering applications and design.

Acoustic Emission-Based Analysis of Damage Mechanisms in Filament Wound Fiber Reinforced Composite Tubes.

This study investigates the mechanical behavior and damage mechanisms of thin-walled glass/epoxy filament wound tubes under quasi-static lateral loads. The novelty is that the tubes are reinforced in critical areas using strip composite patches to provide a topology-optimized tube, and their damage mechanisms and mechanical performance are compared to that of un-reinforced (reference) tubes. To detect the types of damage mechanisms and their progression, the Acoustic Emission (AE) method is employed, accompanied by data clustering analysis. The loading conditions are simulated using the finite element method, and the results are validated through experimental testing. The findings confirm that the inclusion of reinforcing patches improves the stress distribution, leading to enhanced load carrying capacity, stiffness, and energy absorption. Compared to the reference tubes, the reinforced tubes exhibit a remarkable increase of 23.25% in the load carrying capacity, 33.46% in the tube's stiffness, and 23.67% in energy absorption. The analysis of the AE results reveals that both the reference and reinforced tubes experience damage mechanisms such as matrix cracking, fiber-matrix debonding, delamination, and fiber fracture. However, after matrix cracking, delamination becomes dominant in the reinforced tubes, while fiber failure prevails in the reference tubes. Moreover, by combining the AE energy and mechanical energy using the Sentry function, it is observed that the reinforced tubes exhibit a lower rate of damage propagation, indicating superior resistance to damage propagation compared to the reference tubes.

Study on the effects of microstructures on the fracture behavior of an Al-Cu-Mg alloy

In this study, a special fracture delamination in L-T fracture toughness specimens of an Al-Cu-Mg alloy was researched by applying three-dimensional optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) methods. The results indicate that the fracture delamination is contributed by the cracks extending a long distance in the T-direction and extending internally along the L-direction, which can result in a lower fracture toughness value. The fracture delamination is determined by the level of grain flattening and the distribution of the second phases. The flat grains result in a tendency for cracks to extend in the T-direction. At the same time, the unevenly distributed Al2Cu and Al2CuMg phases lead to cracks extending in the L-direction, which eventually causes the formation of delamination fractures. The reduction in grain size can also contribute to weakening the fracture delamination to a certain extent.

Investigating the lap shear adhesion of coir and glass-fibre reinforced epoxy bonding to mild steel with varying volume fractions

Bonding synthetic fibres to metals to improve strength, durability, and corrosion resistance is a prevalent practise in the automotive, marine, and aerospace industries. Lap shear adhesion, a measurement of the bonding strength between composites and metallic substrates, is essential for structural integrity. The emergence of natural fibre composites as sustainable alternatives to synthetic composites makes it essential to investigate their lap shear behaviour and the effect of fibre volume fraction on composite properties. This research investigates the adhesion behaviour of coir and glass fibre epoxy composites to mild steel. Coir fibres, which are known for their resilience and tenacity, were treated with an alkaline solution to improve their adhesion to the resin. Samples of lap shear adhesion were prepared in accordance with ASTM specifications, and tests were conducted using a tensile machine. Increasing the volume fraction of coir or glass fibres decreased the bond strength, as demonstrated by the results. Due to the fibres’ greater tensile strength and rigidity, glass fibre composites exhibited superior strength. However, under tensile loading conditions, coir fibres exhibited superior adhesion to mild steel surfaces. SEM micrographs confirmed that coir composites exhibit shear failure while glass composites exhibit fibre pull-out behaviour. This study concludes by highlighting the engineering potential of coir fibres, considering their natural properties and cost-effectiveness. It is necessary to further optimise the fiber-matrix interface and comprehend the mechanical behaviour of coir composites in order to maximise their effectiveness. To assure the long-term durability of composite-metal joints, surface preparation, adhesive type, application procedure, and environmental conditions must also be considered. At a content percentage of 10%, glass fibres exhibited 100% higher shear strength compared to coir fibres in epoxy composites. Conversely, coir fibres at 10% content demonstrated approximately 75% greater shear strength than the values obtained with 40% glass fibres. The failure mechanisms observed are delamination or fibre fracture in the bonding area under tensile and shear loading. Increasing the fibre volume fraction reduces bond strength. Factors such as limited space for the matrix, tension concentrations, and the mechanical properties of the fibres contribute to weakened bonds. Glass fibres have better strength and rigidity than coir fibres, affecting load transfer and adhesion. Interfacial bonding is crucial, and maintaining it becomes more difficult with higher fibre volume fractions, resulting in weakened bonds.

Long-term evolution of overlying rock fractures in mined-out areas and its effect on gas flow conductivity

Abandoned mines are often closed for long periods, and the overlying rock in mined-out areas is subjected to creep due to constant stress, which affects the overlying rock fracture morphology. The fractures in these rocks have a conductive effect on the gas flow, and previous studies less consider the influence of the long-term evolution process of the fractures on the gas distribution in these areas. Long-term experiments were conducted using a physical similarity experimental model of the mined-out area. To further explain the evolution law of the overlying rock displacement and fracture fields, a method for quantifying the percentage of the fracture field of the overlying rock based on computer image recognition technology is proposed. The results show that the long-term evolution of the overlying rock fractures have the characteristics of transfer and closure, and the change process determines the gas flow trajectory of overlying rock. The long-term evolution of the overlying rock is clarified, which incorporates the three-stage development of the delamination fractures and the stage density increase of the broken fractures. The gas storage capacity of the overlying rock first increases, then decreases, before stabilizing, and the gas diffusion capacity gradually increases. The gas distribution range fluctuates and increases with the evolution of the overlying rock fractures at different times. The time-varying law of the long-term evolution of overlying rock fractures in the mined-out area is explained and theoretical support is provided for clarifying the time-varying law of gas distribution in the overlying rock.

Fatigue delaminations in composites for wind turbine blades with artificial wrinkle defects

Out-of-plane wrinkles are manufacturing defects that affect the structural performance of wind turbine blades under fatigue. Glass Fiber Reinforced Polymer (GFRP) laminated specimens embedded with artificial wrinkle defects at two severity ratios (amplitude/half-wavelength) show different resistance to cyclic loading when tested under tension–compression fatigue. This work presents the validation of a fatigue formulation for the prediction of fatigue damage from wrinkles characteristic of wind turbine blades. The validation is performed through numerical models combined with experimental tests in which the fracture framework aims at predicting crack initiation and delamination propagation. The experimental fatigue program loaded the specimens with R=−1 to assess damage growth. The fatigue damage mechanism is quantified as a stiffness degradation, and the damage level is classified into five phases. Comparing the two severity types of wrinkles, the fatigue lifetime for equal external loading differs by approximately two decades. This difference is also captured by the numerical predictions. The lower the aspect ratio (AR), the higher the defect resistance to reversed fatigue loading. The numerical models captured the qualitative behavior of the SN curves and delamination fracture path and location observed in the experiments.

Effect of rolling temperature and reduction on brick-and-mortar Ti2Ni/TiNi composite

The brick-and-mortar Ti2Ni/TiNi composite, composed of Ti2Ni bricks distributed among TiNi mortars, was successfully produced by hot rolling laminated Ti2Ni/TiNi composite. The rolling temperature and reduction have large effects on brick width and brick interspacing, respectively. When the compression is carried out perpendicular to the stacking direction, all the samples exhibit delamination fracture, which is harmful to mechanical performances. When loading is parallel to the stacking direction, too large brick width and too small brick interspacing both boost the delamination between brittle Ti2Ni and ductile TiNi. After 60% rolling at 700 °C, the brick-and-mortar composite exhibits a largest strength of (1923.11±70.78) MPa and a largest fracture strain of 0.190±0.017 because suitable brick width and interspacing inhibit the delamination and promote crack deflection. Further optimization of mechanical properties can be achieved by the adjustment of brick width and interspacing.

Physico-Mechanical Property Evaluation and Morphology Study of Moisture-Treated Hemp–Banana Natural-Fiber-Reinforced Green Composites

The development of many engineered product applications for automobiles and aircraft parts has initiated the search for novel materials as alternatives to metal matrix composites (MMCs). Natural-fiber-reinforced polymer composites offer distinct advantages such as biodegradability, eco-friendliness, flexibility, low density, and higher specific strengths, etc. This study focuses on natural-fiber (hemp and banana)-fabric-reinforced polymer composites suitable for exterior-engineered parts. The hand lay-up process is used to fabricate these hybrid composites. Exterior-engineered products are highly susceptible to moisture, which can deteriorate their mechanical performances, including their tensile and flexural strength, thereby affecting the durability of the hybrid composites. Therefore, the hybrid composites are subjected to water absorption tests, where samples are immersed in distilled water for week-long intervals. After each interval, the water-absorbed specimens are tested for their tensile and flexural characteristics as per ASTM D-3039 and ASTM D-790, respectively. The moisture treatment had a notable impact on the composite materials, causing a slight decrease in the tensile strength by 2% due to the diminished lateral strength in the interlaminar fibers. Contrary to expectations, the flexural strength of the composites improved by 2.7% after the moisture treatment, highlighting the potential of the moisture treatment process to enhance the elastic properties of such composites. The dimensions of the specimens changed after the water immersion test, resulting in increased longitudinal and decreased lateral dimensions. The surface morphologies of the composite failure samples showed fiber delamination, fiber breakage, voids, and matrix fractures.

Fatigue Behavior of Polymer Encapsulated Graphene to Mitigate Interfacial Fatigue Damage

In applications such as flexible electronic devices, graphene, and other 2D materials are frequently in contact with stretchable polymeric substrates. The interface between 2D materials and polymers is dominated by weak van der Waals forces and can eventually degrade due to the frequent dynamic mechanical loads that these devices experience. This can lead to significant local delamination and shear fracture of the 2D materials. Using the polydimethylsiloxane (PDMS) encapsulation method, it is shown that the damage in graphene is significantly mitigated when it is capped during dynamic loading. To track the spread of damage in both encapsulated and nonencapsulated graphene, in situ, cyclic loading is performed. The fundamental process driving this substantial reduction in damage propagation in the 2D lattice is explained by the conventional shear lag model. It is also observed that softer PDMS substrate and capping layer completely mitigate the fatigue damage in graphene for 100 cycles at 10% applied fatigue strain.

The ductile-brittle transition behaviors of W/Ta multilayer composites

Tungsten (W) usually shows a high ductile-brittle transition temperature (DBTT). To overcome this shortcoming, W-based multilayer composites have been designed. In this study, the ductile-brittle transition behaviors of W/Ta multilayer composites are investigated by uniaxial tensile and three-point bending tests under temperatures ranging from room temperature to 600 ℃. For uniaxial tensile tests, the DBTT of composites bonded at 1000 ℃ is about 200 ℃. However, the DBTT of composites bonded above 1200 ℃ is about 300 ℃. When testing temperature is lower than the DBTT, both the strength and ductility are improved with increasing temperature. The composites exhibit the highest tensile strength at 300 ℃. Meanwhile, the fracture modes of the composites, especially the W layer, changes dramatically at different testing temperature. For the composites bonded at 1000 ℃, the fracture mechanism of W layer changes from brittle cleavage fracture to delamination fracture, and then to ductile shear fracture. For the composites bonded at a temperature above 1200 ℃, the fracture mode of W layer evolves from intergranular fracture to cleavage fracture, then to shear fracture. Compared with uniaxial tensile tests, the DBTT is lower during three-point bending.

Diffusion Barriers Minimizing the Strength Degradation of Reactive Air Brazed Ba0.5Sr0.5Co0.8Fe0.2O3-δ Membranes during Aging.

The separation of oxygen from air by means of inorganic ceramic membranes requires gas-tight ceramic-metal joints that enable reliable permeation operation in the oxygen partial pressure gradient at 850 °C. Reactive air brazing is a promising method to solve this challenge. However, reactive air brazed BSCF membranes suffer from a significant strength degradation that is caused by unhindered diffusion from the metal component during aging. In this study, we investigated how diffusion layers applied on the austenitic steel AISI 314 influence the bending strength of BSCF-Ag3CuO-AISI314 joints after aging. Three different approaches were compared as diffusion barriers: (1) aluminizing via pack cementation, (2) spray coating with NiCoCrAlReY, and (3) spray coating with NiCoCrAlReY and an additional 7YSZ top layer. Coated steel components were brazed to bending bars and aged for 1000 h at 850 °C in air prior to four-point bending and subsequent macroscopic as well microscopic analyses. In particular, coating with NiCoCrAlReY showed low-defect microstructures. The characteristic joint strength was raised from 17 MPa to 35 MPa after 1000 h aging at 850 °C. In addition, the dominant delamination fracture between the steel and the mixed oxide layer, observed in the reference series with uncoated steel, could be replaced by mixed and ceramic fractures of higher strength. The effect of residual joint stresses on the crack formation and path is analyzed and discussed. Chromium poisoning could no longer be detected in the BSCF, and interdiffusion through the braze was effectively reduced. Since the strength degradation of reactive air brazed joints is mainly caused by the metallic joining partner, the findings on the effect of the diffusion barriers in BSCF joints might be transferred to numerous other joining systems.

Effect of heat treatment on the microstructure, impact toughness and wear resistance of Fe-based/B4C composite coating by vacuum cladding

The study focused on the effect of quenching and quenching-tempering processes on the microstructure, hardness, impact toughness and wear resistance of Fe-based/B4C composite coating on the surface of ASTM 1045 steel by vacuum cladding. The results revealed that the metallurgical bonding was realized between the coating and steel substrate. After quenching at 950/1000/1050 °C and quenching-tempering at 1000–490/1000–540/1000–590 °C, the hard phases (M2B and M23 (C, B) 6) in the coating remained unchanged in type, but their morphologies were broken and became more rounded. The coating matrix changed from pearlite to martensite, and granular secondary phases of M23(C, B)6 precipitated from coating matrix. After heat treatment, the impact energy of coated samples is significantly improved, which may be related to the evolution of the coating microstructure and the appearance of interfacial delamination fracture. The results of the wear test showed that the change of coating matrix and hard phase morphology, and the coordination between them were the main factors affecting the wear resistance of the coating. The best wear resistance of the coating was obtained at QT540, and the wear mechanisms were mainly fatigue spalling and brittle fracture.

Insights into the effect of fiber–matrix interphase physiochemical- mechanical properties on delamination resistance and fracture toughness of hybrid composites

Insights into the effect of fiber–matrix interphase physiochemical- mechanical properties on delamination resistance and fracture toughness of hybrid composites

Mechanics of carbon fiber reinforced plastics negative Poisson's ratio structures

Negative Poisson's ratio structure (NPRS) belongs to a type of meta-mechanical material, which has been widely investigated for its robust capacity to absorb impact energy and has the potential to be used for protection during collision. To address the challenge of lightweight NPRS, here the basic concepts of NPRS and how the NPRS may be fabricated using laminated carbon fiber reinforced plastics (CFRP) were discussed. Furthermore, the mechanical behaviour of the CFRP-NPRS was performed by the finite element analysis (FEA). Furthermore, the future application and development of the CFRP-NPRS in lightweight cushioning energy-absorption situations were concluded. The results show that the failure modes of the CFRP-NPRS include cracking, delamination and shear fracture near the corner, and closed structure will occur dislocation deformation. In the combination of the opening structure and closed structure, closed structure dominates the deformation. The NPRE of CFRP-NPRS is only reflected in the inward contraction of the cross-beam. The stress on the beams has an alternative distribution phenomenon, and the 0° fiber layer mainly bears the load.