Ultimate Fracture Research Articles

Experimental and numerical investigation on dynamic deformation and ignition response of NEPE-based propellants

An experimental and numerical study has been conducted to investigate the effects of strain rates on the mechanical responses and ignition mechanism of NEPE-based propellants (Nitrate Ester Plasticized Polyether). The modified split Hopkinson pressure bar (SHPB) equipped with a high-speed camera was used to capture the mechanical-chemical feature images during the whole impact process. The macro-mesoscopic thermomechanical model was employed to describe the viscous shear flow hotspot formation at the mesoscale. The results showed that the mechanical and ignition responses of the NEPE-based propellants are heavily dependent on strain rates. It is observed that the impact processes can be summarized into four stages: homogeneous deformation, shear flowing, initiation of local shear region and ultimate fracture (or ignition). Selected image sequence and SEM images indicate that viscous shear flow is important to the ignition of propellants. The calculated axial stress-strain curves indicate that propellant exhibits a remarkable rate-dependence and viscous effect. The predicted features of hot spot-ignition evolution are consistent with the experimental phenomenon and prove the critical strain rate of ignition is 4500 s−1.

Effects of the Energy Density on Pores, Hardness, Surface Roughness, and Tensile Characteristics of Deposited ASTM 316L Specimens with Powder-Bed Fusion Process.

Powder bed fusion (PBF) is a typical metal-AM process. Studies on the process parameters are required to fabricate the desired shape without defects in the PBF process. The aim of this study is to investigate the effects of energy density on the pore, hardness, surface roughness, and tensile characteristics of deposited ASTM 316L specimens using a powder-bed fusion process. Twenty-seven types of specimens with different laser powers, scanning speeds, and overlap ratios were fabricated using the PBF process. The effects of the energy density on the porosity, hardness, surface roughness, tensile strength, and fracture properties of ASTM 316L specimens were examined. The relationships between these properties and energy density are discussed. A critical energy density level was suggested as 79 J/mm3 considering these characteristics. With the critical energy density level, relative density, surface roughness (Ra) and hardness were observed 99.5%, 1.2 μm, and 240 HV, respectively. Additionally, these characteristics were improved with increasing energy density. Five representative conditions were chosen to fabricate tensile specimens with the ASTM 316L powder through the PBF process. Tensile characteristics, including ultimate strength, yield strength, strain, and fracture shape, were examined for different energy densities. The best tensile characteristics were observed with the highest energy density level of 155 J/mm3.

Theoretical and Experimental Study of the Effect of Plasma Characteristics on the Mechanical Properties of Ihram Cotton Fabric.

Theoretical and experimental investigations of the radial distribution function of the electron temperature (RDFT), for the abnormal glow region in a low-density plasma fluid and weakly ionized argon gas, are provided. The final proved equation of RDFT agrees with the experimental data for different low pressures ranging from 0.2 to 1.2 torr, confirming that the electron temperatures decrease with an increasing product of radial distance (R) and gas pressures (P). A comparison of the two configurations: for the axial distance (L), from the tip of the single probe to the cathode electrode, and the cathode electrode radius (R), shows that, in both cases, the generated plasma temperatures decrease, and densities increase. The RDFT accurately depicts a dramatic decrease for L < R by 60% compared with the values for L > R. This indicates that, when L < R, the rate of plasma loss by diffusion is reduced. Under this investigation, the mechanical characteristics of treated and pre-treated Ihram Cotton Fabric Samples were compared under the Influence of the different two configurations of Plasma Cell discharge: . These characteristics included resiliency, strain hardening, tensile strength, elongation percentage, yield strength, ultimate tensile strength, toughness, and fracture (breaking) point. Furthermore, the mechanism parameters of plasma interaction with textile membrane will be discussed, such as: process mechanism, interaction, and gas type.

Probabilistic risk assessment for the piping of a nuclear power plant: Uncertainty and sensitivity analysis by using SINTAP procedure

For the purpose of probabilistic fracture mechanics estimation in the field of reliability analysis of pressure vessels and piping, a probabilistic method by using SINTAP (Structural INTegrity Assessment Procedures for European Industry) is developed. Monte Carlo simulation (MCS) is applied to investigate the influence of both the uncertainties of random parameters and inspection strategies on the failure probability (FP). A sensitivity analysis with regard to the above-mentioned aspects is conducted to identify the most significant parameters and efficient countermeasures to reduce failure risk in specially-assumed cases. The results of this study point out that the thickness and the inner radius of the pipe have the strongest impact on the FP of the pipe, followed by the bending moment, weld residual stress (WRS), crack length, initial crack depth, yield strength (YS), ultimate tensile strength (UTS), flow strength, fracture toughness, inner pressure and axial force. Compared with the detection quality and the inspection start time, selecting an appropriate inspection interval is a more effective method to reduce the failure risk. All these results provide a reference for the design of piping systems and guide the selection of in-service inspection (ISI) strategies with suitable flaw-detection capabilities and inspection frequencies.

Enhanced oxidation resistance of an AlSi alloy coating via Cr barrier layer insertion

A novel Cr barrier layer was designed for suppressing the interdiffusion of an AlSi alloy coating on stainless steel. Without a Cr barrier layer, the same coating experienced a severe element interdiffusion upon exposure to high-temperature air. The rapid upward movement of the Fe atoms induced the formation of the (FeAl + Fe2Al5) alloy compounds and eventually led to severe volume shrinkage and the ultimate fracture of coating. The significant downward diffusion of the (Al + Si) atoms not only triggered numerous pores but also induced the accumulation of the FeAl alloy compound in the substrate resulting in extreme interfacial cracking. In contrast, a diffusion barrier layer comprising (Cr2O3 + SiO2) and Al2O3 was formed in the coating with a Cr layer during high-temperature exposure, effectively preventing the rapid elemental interdiffusion. Moreover, it inhibited the formation of the (FeAl + Fe2Al5) alloy compounds in the coating as well as prevented the accumulation of the FeAl in the substrate. The obvious upward diffusion of Cr atoms further healed these pores induced by the downward diffusion of (Al + Si) atoms. The strong barrier capability of this composite oxide layer and the healing effect of Cr diffusion eventually led to an improved oxidation resistance of the Cr-coated layer.

Effect of intercritical annealing and subsequent ageing on the microstructure and mechanical properties of a medium Ni–Mn low carbon steel

The aim of this research was to develop a medium Ni–Mn dual phase steel with a combination of relatively high strength and good formability for industrial applications. Accordingly, this research was conducted to examine the effects of intercritical annealing and subsequent ageing treatments on the microstructure and mechanical properties of an Fe-9.5Ni-6.5Mn (wt.%) low carbon martensitic steel. Electron back scattering diffraction (EBSD) analysis revealed that intercritical annealing treatment at 610 °C in the ferrite + austenite (α+γ) dual phase region for various holding times led to formation of the reversed austenite phase in the martensite matrix, producing a medium Ni–Mn dual phase steel. It was resulted that the volume fraction of austenite and its grain size were significantly increased with increasing the holding time. Also, high resolution transmission electron microscope (HRTEM) images illustrated the formation of nano-sized θ-NiMn precipitates within the martensite phase after subsequent ageing at 450 °C for 7.2 ks. Intercritical annealing followed by ageing yielded a good combination of an ultimate tensile strength (∼1160 MPa) and fracture strain (∼11.5%) in the developed dual phase steel compared to the initial martensitic steel. The high strength and good ductility of the developed dual phase steel were respectively attributed to the presence of θ-NiMn precipitates with a hard character and reversely formed austenite with a ductile nature in the microstructure. Furthermore, the fully brittle fracture mode in the aged initial steel changed to a mixture of brittle and ductile behavior in the dual phase steel produced by intercritical annealing and subsequent ageing.

A CoCrFeNiMnSi high entropy alloy showing a good combination of shape memory effect and mechanical properties

We realized a good combination of shape memory effect and mechanical properties in a hot-rolled Fe47.7Mn15.5Co9.8Cr10.8Ni5.1Si11.1 high entropy alloy (HEA) by Si alloying and proper heat treatment to guarantee a low density of annealing twin boundaries. Its maximal recovery strain of 5.7% reached the level that conventional FeMnSi-based and Co-based shape memory alloys (SMAs) showing the same FCC to HCP martensitic transformation can realize. It showed a better combination of ultimate tensile strength and fracture strain than the reported CoCrFeNiMn-based HEAs with FCC matrix did. This result showed that to marry the shape memory effect with the excellent mechanical properties will be a promising direction for developing novel HEAs.

Ultimate strength and fracture failure of hull stiffened plates based on plastic accumulation under cyclic loading

Relying on nonlinear finite element analysis of ANSYS software, the ultimate strength and fracture failure of hull stiffened plates based on plastic accumulation have been studied under cyclic compression and compression-tension load. In addition, the shakedown is also preliminarily discussed. According to different cyclic load patterns, the influence of material models such as elastic-perfectly plastic, isotropic hardening, and Chaboche model on plastic accumulation, ultimate strength, and fracture characteristics of stiffened plates is mainly researched. Studies have shown that material models have a significant impact on the plastic accumulation region, plastic accumulation speed, and the ultimate strength of hull stiffened plates under cyclic loading. As the number of cycles increases, plastic accumulation will cause hull stiffened plates to fracture or reach a shakedown state. When the Chaboche model is adopted, the plastic accumulation speed of hull stiffened plates under cyclic loading is the slowest, and the decrease in ultimate strength is the most moderate. For the cyclic load amplitude and pattern selected in this study, when plastic accumulation causes stiffened plates to fracture, its ultimate strength drops to 24–55% of the first compressive ultimate strength.

Simulation of Combined Stresses and Stress Concentration Factor Effects on a Femur Cortical Bones

The purposes of this article were to obtain mechanical properties of the dry femur cortical bone samples through a tensile load and stress concentration factor approach and to provide simulations to predict experimental behaviors based on manipulations of certain properties and parameters of the biomaterial. Since bone samples have characteristics and geometries, the development of a mathematical model was necessary to describe the combination of stresses interacting in the bone when a tension load is applied. The samples have average diameters and lengths of 0.5 and 2 inches respectively and were tested using a 10 kN Universal Tensile Machine to determine mechanical properties such as yield and ultimate stress, young module, and fracture, among others. Several simulations were conducted to evaluate failure criteria like “Von Mises”, “Tresca” and “Tsai-Wu”. Finally, was concluded that 83% of the data obtained from the 22 samples observed in the “Stress-Strain” charts showed a directly proportional relationship.

A novel image-based approach for interactive characterization of rock fracture spacing in a tunnel face

This paper presents a novel integrated method for interactive characterization of fracture spacing in rock tunnel sections. The main procedure includes four steps: (1) Automatic extraction of fracture traces, (2) digitization of trace maps, (3) disconnection and grouping of traces, and (4) interactive measurement of fracture set spacing, total spacing, and surface rock quality designation (S-RQD) value. To evaluate the performance of the proposed method, sample images were obtained by employing a photogrammetry-based scheme in tunnel faces. Experiments were then conducted to determine the optimal parameter values (i.e. distance threshold, angle threshold, and number of fracture trace grouping) for characterizing rock fracture spacing. By applying the identified optimal parameters involved in the model, the proposed method could lead to excellent qualitative results to a new tunnel face. To perform a quantitative analysis, three methods (i.e. field, straightening, and the proposed method) were employed in the same study and comparisons were made. The proposed method agrees well with the field measurement in terms of the maximum and average values of measured spacing distribution. Overall, the proposed method has reasonably good accuracy and interactive advantage for estimating the ultimate fracture spacing and S-RQD. It can be a possible extension of existing methods for fracture spacing characterization for two-dimensional (2D) rock tunnel faces.

Effects of Zn addition on microstructure and tensile properties of Mg–Y–Co alloy

Effects of Zn addition on microstructure and mechanical properties of the extruded Mg97.8Y1.4Co0.8 (at.%, WC) alloy were investigated at room temperature. It was found that the as-cast WC alloy was mainly composed of α-Mg, MgYCo4, Mg3(Co,Y) and 15R-LPSO phases distributed at the grain boundary. All particles of as-homogenized WC alloy were remarkably refined after extrusion, but there was no phase transition during the subsequent homogenized and extruded states. With the replacement of Co from Zn, the as-cast Mg97.8Y1.4Co0.2Zn0.6 (at.%, WZC) alloy consisted of α-Mg, 18R-LPSO with lamellar and blocky shape, and a small amount of rich-Y phases. Parts of 18R-LPSO phases transformed into fine 14H-LPSO phases and stacking faults (SFs) in the grain interior during homogenization and extrusion. The extruded WZC alloy exhibited a smaller average grain size (∼3.2 μm) than the extruded WC alloy (∼3.9 μm) owing to fully dynamic recrystallization (DRX). Both the extruded WC and WZC alloys had a basal plane texture parallel to the normal direction (ND). Tensile testing results indicated that the Zn replacement improved tensile strengths of the extruded WC alloy and maintained the high elongation of the alloy (∼32.2%). The tensile yield strength, ultimate tensile strength and fracture elongation of the extruded WZC alloy were 212 MPa, 281.5 MPa and 32.2%, respectively. The alloy exhibited a good strength and ductility balance. The high tensile strengths of the extruded WZC alloy at room temperature were mainly attributed to grain refinement and the precipitation strengthening of different particles, and the good ductility was mainly due to grain refinement and texture weakening.

Numerical Analysis of Unidirectional GFRP Composite Mechanical Response Subjected to Tension Load using Finite Element Method

Composite material is a well-known structural material which is increasingly adopted as an engineering structure material. Glass fiber reinforced polymer offers the lightweight and high strength characteristics that is required for the modern industry, such as aviation, automotive, wind power, and marine technology. One of the important mechanical characteristics of the composite materials are the tensile properties, because it is well known as the material strength. Therefore, the investigation of mechanical response on the glass fiber reinforced polymer (GFRP) tensile test using numerical analysis is important for the estimation of structural response of the GFRP complex structure, such as boat construction. The objective of this research is to assess and estimate the mechanical response of the GFRP composite material subjected to tension load using finite element method. The linear transversely isotropic model is developed to estimate the unidirectional glass fiber GFRP with the configuration of fiber orientation angles of 0°, 30°, 45°, 60° and 90°. The results show that FE simulation are capable to detect the specimen response during the tensile test. The maximum discrepancy of the estimated stress strain diagram is about 16.5% to 32% compared to experimental data. The larger orientation angle has shown the larger discrepancy value. It is found that the increment of discrepancy value is generated by the nonlinearity behavior of the material due to the domination of polymer material behavior on the large orientation angle. Otherwise, the FE models have estimated accurately the ultimate strength, maximum displacement and fracture load. It can be concluded that the linear transversely isotropic model is adequately accepted as the estimation method of the GFRP composite structure response.

Analysis on exceptional cryogenic mechanical properties of AA2219 alloy FSW joints in multi-scale

In this paper, the multi-scale strain characteristics of AA2219 alloy friction stir welded joints deformation at cryogenic temperature were analyzed quantitatively. The macro strain distribution of the joints was analyzed using the quasi in-situ DIC technology during uniaxial tension at room and cryogenic temperature −196°C. The mesoscopic/microscopic strain distribution were studied by SEM-DIC, EBSD and geometric phase analysis. The results show that ultimate fracture strain of the FSW joints increased from 0.16 to 0.28 with an increase of 75% and the strain heterogeneity of the joints was significantly reduced at −196°C. The major strain of the weld zone increased by 128.2%. The mesoscale local strain decreased by 32.4% and 25% in the base metal and weld zone, respectively. The microscale deformation localization between grains was improved, and the dislocation distribution within the grains was more uniform in nanoscale level. The improved strain localization in multi-scale levels at cryogenic temperature contributed to the superior mechanical properties of the joints. At −196°C, the decreased strain heterogeneity was related to the decreased strength differences between the weld and BM zone directly. The intergranular deformation uniformity of the fine-grained weld zone were improved at cryogenic temperature. The ductile micro-voids coalescence instead of connecting along the slip bands rapidly contributed to the increased plasticity of weld zone at −196°C, and the cryogenic plastic deformation was dominated by the activated cross and multi-slips. The ability to resist strain concentration caused by local slip was improved at ultra-low temperature.

Saline tolerant tough-yet-strong fiber-reinforced gel-nacre for soft actuator

Fiber-reinforced hydrogel (FrH) possesses the capability as flexible structural materials. The state-of-the-art FrH left a number of key issues untouched, including interfacial effects and the tolerance against salt disturbance. Herein, we report a saline-tolerant and strong-yet-tough FrH. This is achieved by infiltrating gel-nacre matrix into a polyaramid fabric via a multiscale reinforcement at the interface. The incorporation of strong yet geometrically compliant fabric skeleton into saline-induced shrinking gel-nacre matrix with mechanical superiority resolves the swelling mismatch between swollen hydrogel and rigid fiber, relieving the trade-off property between strength and toughness. Such integration leads to a tight interfacial binding between both components, where fabricated FrH can sustain its structure up to 5 months in artificial sea water yet exhibit superior tough-yet-strong mechanical performances, i.e., ultimate fracture strength of 111.6 MPa, toughness of 383.3 MJ/m3, and fracture energy of 195.8 kJ/m2. The prototype of a bilayer petalage-like actuator that reversibly transfers from 2D to 3D structure in water and saline driving by osmotic pressure gradient was demonstrated. These inspiring results open the door for developing flexible, tough yet stable materials for applications in salty environments including soft robots, energy absorption structural materials, etc.

Bending Failure Behavior of the Glass Fiber Reinforced Composite I-Beams Formed by a Novel Bending Pultrusion Processing Technique

Abstract The glass fiber reinforced resin matrix composite I-beams were designed and formed via a type of novel bending pultrusion processing technique, and the three-point bending tests were carried out to analyze the mechanical bending performances. The obtained results show that the main failure mode of the composite I-beam under the bending load is the upper structure (top flange) cracks along the length direction of the fibers, and the cracks simultaneously propagate downwards in the vertical direction. The bifurcated cracks can be found at the junction area between the top flange and web. In addition, the main bending failure mechanism of the composite I-beam includes the matrix cracking, propagation of cracks, and final fracture failure. In particular, noting that when the crack reaches the I-shaped neck position, the lateral bifurcation occurs, and the resulting secondary cracks further extend in two directions, which leads to the serious damage between the top flange and web, and the ultimate fracture failure occurs.

Thermal and mechanical characterization of nanoporous two-dimensional MoS2 membranes

For practical application, determining the thermal and mechanical characterization of nanoporous two-dimensional MoS2 membranes is critical. To understand the influences of the temperature and porosity on the mechanical properties of single-layer MoS2 membrane, uniaxial and biaxial tensions were conducted using molecular dynamics simulations. It was found that Young’s modulus, ultimate strength, and fracture strain reduce with the temperature increases. At the same time, porosity effects were found to cause a decrease in the ultimate strength, fracture strain, and Young’s modulus of MoS2 membranes. Because the pore exists, the most considerable stresses will be concentrated around the pore site throughout uniaxial and biaxial tensile tests, increasing the possibility of fracture compared to tensing the pristine membrane. Moreover, this article investigates the impacts of temperature, porosity, and length size on the thermal conductivity of MoS2 membrane using the non-equilibrium molecular dynamics (NEMD) method. The results show that the thermal conductivity of the MoS2 membrane is strongly dependent on the temperature, porosity, and length size. Specifically, the thermal conductivity decreases as the temperature increases, and the thermal conductivity reduces as the porosity density increases. Interestingly, the thermal and mechanical properties of the pristine MoS2 membrane are similar in armchair and zigzag directions.

Effect of Cl−-induced corrosion on the mechanical properties of reinforcing steel embedded in ternary concretes containing FA and UtSCBA

Mechanical properties of rebars embedded in ternary concretes with fly ash (FA) plus untreated sugarcane bagasse ash (UtSCBA) and immersed in a Cl−-solution for 3000 days were investigated. Reinforced concrete specimens containing Portland cement (PC) only, PC + FA, and PC + FA + UtSCBA were manufactured. The corrosion conditions of the rebars were evaluated by electrochemical testing; then the rebars were extracted and their mass loss estimated. Next, elemental mapping of the concrete/reinforcing steel interfaces using scanning electron microscopy was conducted. Rust was analyzed by X-Ray diffraction and infrared spectroscopy. Finally, the rebars were tested in tension to evaluate their yield and ultimate strengths, fracture loads, and ductilities. Results indicate that rebars from UtSCBA-ternary concretes experienced the lowest mass loss. Moreover, the yield strengths of all rebars were not affected by corrosion, while the ultimate strengths, fracture loads, and ductilities of rebars from UtSCBA-ternary concretes were larger than those from the control.

The fracture toughness analysis on the basalt fiber reinforced asphalt concrete with prenotched three-point bending beam test

In this study, the fracture resistance of the basalt fiber reinforced asphalt concrete (BFRAC) constructed in The Republic of Mozambique was investigated with prenotched three-point bending beam tests. Fracture energy and the double-parameter fracture model, i.e., initial fracture toughness (Ki), and ultimate fracture toughness (Ku), were utilized to evaluate the fracture behaviors of BFRAC. The test results indicate that the double-parameter fracture model proposes more rational and convincing explanations to the BFRAC over the fracture energy. According to the double-parameter fracture model, a remarkable enhancement on fracture resistance of BFRACs with 4.5% and 5.0% ratios achieved as the fiber content increased while a gradual increase exhibited for the fracture resistance of BFRAC with 4.0% b/a ratio and 0.2% fiber. It indicates that the fracture resistance of BFRAC will be enhanced with the increase of the basalt fiber dosages as long as the asphalt volume is enough for wrapping aggregates and basalt fiber, causing more cohesive and adhesive capacity.

High strength and ductility of an additively manufactured CrCoNi medium-entropy alloy achieved by minor Mo doping

The effect of minor Mo doping on the microstructure and mechanical properties of a (CoCrNi)95Mo5 medium-entropy alloy (MEA) was studied by selective laser melting (SLM) to architect the dislocation-formed sub-grains, ultrafine (Mo, Cr)-enriched μ precipitates and various lattice defects. High strength and ductility were achieved in the as-SLMed (CoCrNi)95Mo5 alloy, where the yield strength, ultimate tensile strength (UTS) and fracture strain were 0.79 GPa, 0.97 GPa and 35.9%, respectively. The superior mechanical properties were associated with the typical hierarchical microstructure that were featured by the high-density dislocations-formed equiaxed sub-grains, the columnar sub-grains separated by low-angle grain boundaries (LAGBs), the fine (Mo, Cr)-enriched μ precipitates and the lattice defects including dislocations, stacking faults (SFs) and Lomer-Cottrell locks (LCs) in the matrix. The results have demonstrated the potential of applying precipitation strengthening in CoCrNi-based MEAs through additive manufacturing to achieve superior mechanical properties.

Nonlinear Finite Element Calculation of Cold Gas Inflator Housing Ultimate Breakage Load

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;For cold gas Inflator, high refinement of ultimate pressure load forecast of inflator housing is one key of Inflator development. For inflator housing hydro-burst test ultimate load calculation, nonlinear finite element software for high precision results. At beginning, the material parameters of inflator housing for simulation is correlated. The FEA material model adopts the stress-strain data from uniaxial tensile experiments. Considering the geometrical nonlinearity resulting from large deformation as well as material nonlinearity from plastic hardening, the whole tensile process from tensile deformation to failure of the specimen is simulated. Numerical results show that the simulation is appropriate to predict the entire deformation process, and simulation results of ultimate tensile load, X-shape distribution of concentrated instability zone, the fracture location and inclined angle all agrees with that of test results.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;After finishing the correlation of uniaxial tensile test and getting accurate material parameters of inflator housing, the ultimate breakage load of inflator housing under hydro-burst test is calculated by FEA software. The discrepancy between FEA calculation and real test of inflator housing breakage pressure was 3.6%, and the deformation and failure position of inflator housing were in good agreement with the test results also. At the same time, the change rules of stress and strain in each direction at the key positions of uniaxial tensile test and hydro-burst test are summarized, then a method to judge the fracture strain according to the stress change trend is proposed. The judged fracture strain by the method corresponds to the test results. The simulation and test results show that the analysis method used in this paper can obtain the ultimate failure load and fracture strain of the inflator housing with high precision.&lt;/div&gt;&lt;/div&gt;