Reduction In Yield Strength Research Articles

Role of Al element in tailoring the austenite mechanical stability and tensile properties of medium Mn steels

Al is generally employed as a key alloying element to tailor the austenite mechanical stability and mechanical properties in medium Mn TRIP steels. However, the effect of Al on the austenite stability has been limitedly studied, leaving contradictory results without a self-consistent explanation. This study addressed this issue through a systematic study of medium Mn TRIP steels with compositions of 0.2C–8Mn-0/1.5/3Al (wt.%), while providing new insights into the factors influencing austenite stability and mechanical properties. It was found that the variation of the Mn distribution in austenite from non-equilibrium to near-equilibrium state and the weakened strain incompatibility between phases due to sufficient recovery of tempered martensite can be achieved with the addition of Al, which contributed to slowed strain-induced martensite transformation (SIMT) and improved austenite stability in the experimental steels annealed at low temperatures in the two-phases region, resulting in a decrease in ultimate tensile strength (UTS) and an increase in total elongation (TE). Furthermore, fully recovered tempered martensite with the hardness much lower than that of austenite was obtained in the 3Al steel annealed at a high temperature in the two-phase region, which led to a significant reduction in yield strength and thus low UTS. Meanwhile, heterogeneous strain distribution was induced by the remarkable gap in hardness between the two phases, which can be responsible for the relatively high austenite mechanical stability. The varying strain states and variation of Mn distribution in austenite can be achieved for the medium Mn TRIP steels with different Al contents, contributing to a wide range of UTS&TE combination with high strength and elongation product (≥40 GPa·%). And the elucidation of the effect of different strain states also opens a new window to adjust the austenite stability and mechanical properties of medium Mn TRIP steels.

Web crippling design of cold-formed high strength steel SHS and RHS at elevated temperatures

This study investigates the web crippling capacities of cold-formed high strength steel (CFHSS) hollow structural section members at elevated temperatures. A numerical investigation on square and rectangular hollow sections (SHS and RHS) undergoing web crippling was performed at various temperatures from 21 °C to 1000 °C. Finite-element (FE) models were firstly developed to replicate the available web crippling tests on CFHSS SHS and RHS members. After validation, extensive parametric studies with 784 specimens covering all four codified web crippling load cases in the current cold-formed steel design specifications were performed. The reductions of web crippling capacities at elevated temperatures were compared against the corresponding yield strength and elastic modulus reduction factors of the materials. The suitability of available web crippling design provisions in current codes of practice and literature to CFHSS sections at elevated temperatures was evaluated. Comparison results reveal that the direct strength method (DSM) previously proposed by the authors at ambient temperature could be extended to elevated temperature conditions and would provide rather consistent and reliable predictions than other existing provisions. A modified DSM is put forward in this paper and it is found that the modified DSM is suitable for web crippling design of the CFHSS sections at both elevated and ambient temperatures, and moreover, can also be used for cold-formed stainless steel SHS and RHS of various grades. Therefore, the modified DSM is recommended to be used for web crippling design of CFHSS and stainless steel SHS and RHS at elevated and ambient temperatures.

Influence of fire-resistant coating on the physical characteristics and residual mechanical properties of E350 steel section exposed to elevated temperature

PurposeMost of the industrial buildings which are designed to moderate loads are constructed using light gauge cold-formed steel (CFS) sections. Residual mechanical properties of CFS sections exposed to elevated temperature need to be investigated as it is necessary to predict the deterioration of elements to avoid failure of the structure or its elements. Also, it would be helpful to decide whether the structural elements need to be replaced or reused. The use of fire-resistant coatings in steel structures significantly reduces the cost of repairing structural elements and also the probability of collapse. This study investigates the effect of fire-resistant coating on post-fire residual mechanical properties of E350 steel grade.Design/methodology/approachIn this study, an attempt has been made to evaluate the residual mechanical properties of E350 steel. A tensile coupon test was performed for the extracted specimens from the exposed CFS section to determine the mechanical properties. Four different fire-resistant coatings were selected and the sections were coated and heated as per ISO 834 fire temperature curve in the transient state for time durations of 30 minutes (821°C), 60 minutes (925°C), 90 minutes (986°C), and 120 minutes (1,029°C). After the exposure, all the coupon specimens were cooled by either ambient conditions (natural air) or water spraying before conducting the tension test on these specimens.FindingsAt 30 min exposure, the reduction in yield and ultimate strength of heated specimens was about 20 and 25% for air and water-cooled specimens compared with reference specimens. Specimens coated with vermiculite and perlite exhibited higher residual mechanical property up to 60 minutes than other coated specimens for both cooling conditions. Generally, water-cooled specimens had shown higher strength loss than air-cooled specimens. Specimens coated with vermiculite and perlite showed an excellent performance than other specimens coated with zinc and gypsum for all heating durations.Originality/valueAs CFS structures are widely used in construction practices, it is crucial to study the mechanical properties of CFS under post-fire conditions. This investigation provides detailed information about the physical and mechanical characteristics of E350 steel coated with different types of fire protection materials after exposure to elevated temperatures. An attempt has been made to improve the residual properties of CFS using the appropriate coatings. The outcome of the present study may enable the practicing engineers to select the appropriate coating for protecting and enhancing the service life of CFS structures under extreme fire conditions.

A Case Study on Condition Assessment of Fire-Damaged RC Members of Turbo-Generator

Many researchers across the globe have carried out fire safety risk analysis to gather evidence and pertinent data for different Reinforced Cement Concrete (RCC) members exposed to fire. Assessment of fire-damaged structures furnishes the minute details of the effect of fire on the properties of concrete.The study indicates the condition assessment of the turbo-generator (TG) unit, comprises of concrete bearing pedestals, deck and supporting columns. The research was conducted using Non-Destructive Testing (NDT) techniques using Rebound hammer test, Ultrasonic Pulse Velocity (UPV) test, Concrete Cover measurement, Carbonation and Crack depth measurements followed by microstructural studies using an X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Optical Microscope (OM), and Mercury Intrusion Porosimetry (MIP). The samples were taken from a fire-damaged concrete bearing pedestal B2 and a non-fire-damaged concrete bearing pedestal B4 of the TG unit. The approach enabled us to find the extent of damage to the RCC members exposed to fire. The above mentioned test witnessed that the concrete bearing pedestal B2 was the moderately distressed member, expressed doubtful quality of concrete, higher porosity, reduced residual compressive strength and reduction in yield strength of steel. However minor distress in form of crushing at the top grout portion was observed in concrete bearing pedestal B4, and no apparent distress was observed in supporting columns of TG unit. Based on the distress identified, repair and remedial measures were proposed to concrete bearing pedestals in order to improve the performance of the TG unit.

Synthesis of Ni-Cu Heterostructures with SPS to Achieve a Balance of Strength and Plasticity

The balance between strength and plasticity has always been an urgent problem for researchers to solve. In this experiment, Ni-Cu heterostructures (HSs) were synthesized by spark plasma sintering (SPS), rolling deformation, and subsequent heat treatment. The density of the Ni/Cu interface of Ni-Cu HS materials can be independently tuned, and thus the effect of hetero-deformation-induced (HDI) strengthening in Ni-Cu heterostructures can be tuned. The density of the Ni/Cu interface is tuned by adding Cu with different volume fractions to obtain the best combination of strength and plasticity. Compared with the previous HSs, the hardness differences between different regions of Ni-Cu HSs are more significant, and they are all composed of single substances. The hard Ni domain and the soft Cu domain are not only different in phase composition but also different in grain size. More interestingly, the density of the hard/soft domains can be adjusted independently, which provides a new way to explore the strength and plasticity balance of HS materials. The yield strength of Ni-Cu HS materials first increases and then decreases gradually with the increase in the Cu volume fraction. When the Cu volume fraction is less than 30%, the HDI strengthening effect in the Ni-Cu HS material can offset the effect of the yield strength reduction caused by Cu; with a further increase in the Cu volume fraction, the HDI strengthening effect is less than the yield strength reduction effect brought on by Cu.

Extreme flooding and reduced salinity causes mass mortality of nearshore kelp forests

Extreme flooding due to climate-induced increases in storm frequency and intensity may negatively impact marine species and habitats. These impacts may be particularly severe in nearshore marine systems where freshwater influx and reduced salinity will be most apparent. In March 2021, severe storms associated with an intense La Niña occurred along 450 km of the east Australian coast causing widespread flooding and freshwater incursion into estuaries and nearshore marine systems. These floods were linked to widespread kelp mortality (Ecklonia radiata) in nearshore systems, particularly near and within estuaries. We quantified levels of kelp mortality with distance from the entrance and depth in one of the most impacted estuarine embayments, Port Stephens. Experiments were conducted to confirm that the flood-induced reduction in salinity was the primary cause of the observed mass mortality of kelp sporophytes and to determine the likelihood of recovery from surviving gametophytes. Floods caused a ∼50% net loss of kelp within the embayment, with almost 100% mortality at shallow depths (<4 m) and increased loss with increased distance from the embayment mouth. Experiments verified that reduced salinity, at levels comparable to those during the floods, caused severe reductions in kelp health, photosynthetic yield and tissue strength. Contrastingly, experiments on gametophytes revealed that they were resilient to short-term reduced salinity. This likely facilitated the rapid recovery of kelp that was observed seven months after the floods. Overall, we identified that future increases in climate-induced severe weather and storms events are likely to increasingly impact kelp and the ecosystems they underpin in nearshore systems.

Effects of heat treatments on microstructure and mechanical properties of laser melting multi-layer materials

The effects of different heat treatments on the microstructure and mechanical properties of the laser melting nickel-based superalloys were systematically investigated. The strength improvement of the heat-treated material was mainly derived from the aging treatment, which converted the γ matrix together with Niobium to the strengthening phases γ′′ and γ′. The solution treatment dissolved partial Laves phases to form the short-acicular δ phases in the remelting zone (RZ), whereas the homogenization treatment dissolved most precipitates including the Laves phase and δ phase, leading to significant grain coarsening in the multi-layer material. Moreover, based on the instrumented indentation reverse analysis, RZ shows consistent stress–strain relationships after the heat treatments, reaching the same level as the heat-treated base material (BM). The remelting-affected zone (RAZ) reveals more outstanding mechanical properties after the direct aging (DA) treatment for the work hardening contributed by dislocation strengthening. Additionally, the residual stresses and deformations in RAZ provide an extra thermodynamic driving force for the grain recrystallization and the formation of the short-clavate δ phase in the solution-treated RAZ. The remaining large grains and small Taylor factor in RZ are considered to lead to a reduction of the mesoscopic yield strength, which cannot be identified in microscopic indentation analysis. The DA heat treatment is recommended for the strength improvement of the laser melting materials.

Hot isostatic pressing of laser powder-bed-fused 304L stainless steel under different temperatures

Hot isostatic pressing (HIP) is becoming a key strategic technology for post-processing metallic materials fabricated with laser powder bed fusion (LPBF), acting to eliminate the processing-induced pores and improve the mechanical properties. This paper comprehensively investigated material characteristics (porosity, residual stress, microstructures, phase composition, and inclusion), mechanical properties (microhardness, tensile properties, and fatigue properties), and deformation behaviors of LPBF 304L austenitic stainless steel (ASS) subjected to HIP process with different temperatures (965°C, 1165°C, and 1365°C). Experimental results indicated that the grain size, inclusion size, recrystallization fraction, and dimple size increased with increasing HIP temperature, which resulted in homogenized microstructure, reduced yield strength and microhardness, and significantly improved ductility. The fatigue life of HIP-treated samples after surface post-treatment was mainly influenced by porosity, inclusion, residual stress, and dislocation density. The HIP-1165°C samples with low porosity and small-sized inclusions had a higher fatigue life than HIP-965°C and HIP-1365°C samples. In addition, the evolution of crystallographic texture and inclusion composition associated with the HIP temperature were systematically revealed with the aid of orientation distribution function (ODFs) and elemental mappings. This study provides a profound understanding of the rational design of the hybrid process of LPBF and HIP.

Effect of composition and microstructure on the rusting of MS rebars and ultimately their impact on mechanical behavior

Rebar steel is used for reinforcement to aid concrete because concrete does not sustain tension. Thermomechanical treatment is an advanced manufacturing technique for rebar production, but rusting problems emerged in the local steel industry. Raw material sampling included ingot casting (IC) and continuous casting (CC). IC samples corroded more frequently than CC samples. Spectroscopy indicated a small amount of chromium and an improper ratio of manganese to sulfur in IC samples. The improper ratio of manganese to sulfur in IC samples promoted hot cracking at grain boundaries, which resulted in intergranular corrosion. The microstructural results of G40 (air cooled) and G60 (water cooled) showed ferrite and martensite in different proportions. The deformed ferrite in G60 indicated inclination to corrosion, and no proper stable layer of martensite was found. The percentage of martensite was not enough to retaliate against intergranular corrosion. Highly pressurized water initiated pitting corrosion due to the formation of small pits on the surface. Tensile testing revealed 10% reduction in ultimate strength, 8% reduction in yield strength, and 30% reduction in percentage of elongation of corroded samples. Environmental study revealed that the humidity level in the industry was greater than in the laboratory space. High values of SOxand NOxemission revealed the involvement of the environment in the deterioration of the product surface.

Development and experimental testing of the technology for producing deformed bars of D16(T) alloy from continuously cast billets of small diameter with low elongation ratios

The article describes the development and pilot-scale testing of the technology for producing bars of the D16(T) aluminum alloy by radial-shear rolling from continuously cast billets with a diameter of 72 mm in several passes. The actual dimensions of rolled bars were within the ±0.16 mm tolerance for all bar diameters, which significantly surpasses the GOST 21488-97 requirements. According to the results of tensile tests, the values of ultimate strength, conventional yield strength, relative elongation and relative reduction were determined. Ultimate strength and relative elongation requirements specified by regulatory documents for the D16(T) alloy were met with a total elongation ratio of more than 4.2. In terms of plastic properties, the obtained bars surpass the GOST requirements by 2.1–2.5 times in the entire range of elongation ratios investigated starting from 2.07. At the same time, there is an increase in the relative elongation by 5.7–6.8 times in comparison with the initial cast state. The microstructure and morphology analysis conducted for secondary phases showed that with a decrease in the bar diameter (with an increase in the total elongation ratio), the average particle size of the α(AlFeMnSi) phase insoluble in the aluminum matrix decreases, which is a consequence of deformation processes developed during rolling. Additional grinding of inclusions during deformation processing can significantly reduce the possible negative effect of the insoluble phase on the mechanical properties of resulting bars, in particular on the plasticity properties. The microstructure analysis showed that bars after rolling and heat treatment are free from cracks, looseness, delamination, and other defects and meet the requirements of GOST 21488-97.

Mechanical properties of bridge-steel weldments at elevated temperatures

The fire-resistance design of welded steel bridges depends on the temperature-dependent mechanical properties at elevated temperatures. This study investigates experimentally the temperature-induced degradation of the mechanical properties of a bridge-steel weldment. A butt-welded joint, containing the base metal (BM) Q345qD steel and weld metal (WM), was welded via submerged arc welding. Monotonic tension tests of BM and WM cylindrical specimens were carried out under various temperatures in the range of 20–700 °C, and their stress-strain relationships, failure modes, yield strength, elastic modulus, and ultimate strength at elevated temperatures were obtained and analyzed. The reduction factors of yield strength, elastic modulus and ultimate strength are compared with those recommended in current design codes. It is shown that elevated temperatures can decrease significantly the material performance of the Q345qD weldment, and the degradation of the mechanical properties of the BM and WM differs with increasing temperature. The test data indicate that the reductions in yield strength, elastic modulus, and ultimate strength at 700 °C from those at 20 °C are 78%, 55%, and 84%, respectively, for the BM and 75%, 53%, and 79%, respectively, for WM. The predictive equations for characterizing the material properties and stress-strain relationships of the BM and WM at elevated temperatures are proposed, thereby providing essential data for evaluating the fire response of steel bridges.

Simulation Study on the Defect Generation, Accumulation Mechanism and Mechanical Response of GaAs Nanowires under Heavy-Ion Irradiation.

Nanowire structures with high-density interfaces are considered to have higher radiation damage resistance properties compared to conventional bulk structures. In the present work, molecular dynamics (MD) is conducted to investigate the irradiation effects and mechanical response changes of GaAs nanowires (NWs) under heavy-ion irradiation. For this simulation, single-ion damage and high-dose ion injection are used to reveal defect generation and accumulation mechanisms. The presence of surface effects gives an advantage to defects in rapid accumulation but is also the main cause of dynamic annihilation of the surface. Overall, the defects exhibit a particular mechanism of rapid accumulation to saturation. Moreover, for the structural transformation of irradiated GaAs NWs, amorphization is the main mode. The main damage mechanism of NWs is sputtering, which also leads to erosion refinement at high doses. The high flux ions lead to a softening of the mechanical properties, which can be reflected by a reduction in yield strength and Young’s modulus.

Effect of expanded glass particle size on compressive properties of vinyl ester syntactic foams

AbstractThe most common fillers for syntactic foam development are glass microballoons or fly ash cenospheres. However, the need for improved properties and reduced cost requires exploring other possibilities. In this work, syntactic foams of vinyl ester resin reinforced with expanded glass particles (EG) were fabricated and compressive properties of the composites were studied. The foam EGS was reinforced with smaller particles of size 0.04–0.125 mm in 15, 30, and 45 vol.% and EGL had larger particles of size 0.25–0.5 mm in 15 and 30 vol.%. Compression testing reveals that 45 vol.% smaller particles enhance the modulus of the EGS foam by up to 48% with a 3.4% reduction in yield strength compared to neat resin. Strain rate sensitivity was observed in both the modulus and yield strength values for all composites. Composite EGS with 15 and 30 vol.% filler showed better strength and modulus than the neat resin at 0.01 s−1 strain rate, which is an overall improvement in the material. When compared with the literature data, the foams made in the present work have the highest compressive strength and modulus for the same density.

Study on the Time‐dependent Reliability of Corroded Reinforced Concrete Bridge Structures due to Ship Impact

The cumulative damage caused by chloride ion erosion to coastal bridge structures reduces the ship impact resistance of channel bridge structures and leads to changes in reliability of bridge structures on ship impact. It is of great theoretical and practical significance to study the performance degradation change law of corroded bridge structures and to evaluate the ship impact time‐dependent reliability of in‐service corrosion‐damaged bridge structures. Based on the durability decay model of reinforced concrete structures in a chloride ion erosion environment, the time‐dependent resistance analysis of bridge structures is carried out considering the reduction of yield strength of longitudinal reinforcement and hoop reinforcement in pile sections and the decay of compressive strength of protective layer concrete. Based on the study of the probabilistic model and parameters of random variables affecting the time‐dependent reliability of ship‐bridge collision, the typical damage modes of bridge structures under ship impact are analyzed, the time‐dependent reliability analysis model of bridge structures under ship impact is established based on the structural damage criterion, the ship‐bridge crash limit state functional function is given, and the time‐dependent reliability analysis of ship‐bridge collision is carried out based on the response surface method.

Determination of structural reliability of a reinforced concrete slab under fire Load

Four reinforced concrete rooms are used in this study, with varying floor areas, openings, and fuel loads. These rooms are office, Classroom, computer, and chemical laboratories of institutional buildings. The time versus Eurocode (EC) parametric fire relationship is determined and compared with ISO 834 and ASTM 119. The performance of the slab is evaluated based on the EC target reliability index of 3.8 for 50 years design period using the First Order Reliability Method (FORM). The probability of failure and structural reliability of each fire compartment at different fire duration is determined. Variables used were concrete compressive strength, a reduction factor of concrete compressive strength, steel yield strength, concrete cover, slab depth, unit width, and area of steel reinforcement provided. The reliability is determined at each 30 minutes fire duration for all fire compartments. The starting point is ambient temperature, then after every thirty minutes until the time when the maximum gas temperature is reached. The fire compartments were able to show fire resistance for two hours and then started to drop over time. Yield strength reduction factor, concrete cover, and area of reinforcement respectively were the most significant variables to determine the reliability index. The structure was able to withhold fire until two hours with a reliability of more than 3.8after that, the slab reliability was less than the target reliability and will need a repair.

Effect of sintering temperature on microstructures and mechanical properties of ZK60 magnesium alloys

In this study, ZK60 Mg alloys were prepared via hot-press sintering under a constant pressure of 30 MPa as well as Ar atmosphere. The sintering temperature was determined to be in the range of 450 °C–600 °C with an interval of 50 °C. The effect of sintering temperature on the microstructures and mechanical properties of the alloys was investigated. All the four sintered alloys mainly exhibited an α-Mg-phase structure and equiaxed grain microstructure. However, a specific amount of melt, enriched in Zn element, formed when the sintering temperature reached 500 °C. Thus, only the alloy sintered at 450 °C maintained the nominal composition of the alloy powder, and exhibited the favorable yield strength and hardness, which was 135.1 MPa and 57 HV, respectively. The alloys sintered at 550 °C and 600 °C exhibited a reduced yield strength and hardness due to the loss of Zn element.

Investigation of steel wire mechanical behavior and collaborative mechanism under high temperature

This study investigated the high-temperature mechanical properties and collaborative working mechanism of zinc-5% aluminum-mixed mischmetal alloy-coated steel strand cables (M-C cables) and internal steel wires by numerical analysis, based on the experimental data for the high-temperature mechanical properties of steel wire. The high-temperature mechanical properties of zinc-5% aluminum-mixed mischmetal alloy-coated steel (M-C steel) with round and Z-shape cross-section shapes were studied in the temperature range of 30–800 °C using the constant temperature loading test method. The two-stage Ramberg-Osgood model for M-C steel wires at elevated temperatures is proposed for modeling of the M-C steel wires. Furthermore, the equations for the reduction in the nominal yield strength, elastic modulus and ultimate strength for M-C steel wires at elevated temperatures are proposed. Numerical analysis and investigation of the high-temperature mechanical properties of normal M-C cables and locked M-C cables under eight temperature conditions are carried out. Based on the high-temperature constitutive relationship of the round and Z-shaped M-C steel wires obtained experimentally, the thermostatic drawing process is simulated at different temperatures for two types of M-C cables. The high-temperature stress-strain relationship between the two and the relevant high-temperature mechanical performance index were obtained. According to the numerical simulation results, the energy, contact stress distribution and radial displacement deformation of M-C cables under the different temperature condition were evaluated and analyzed. The collaborative working mechanism of M-C cabled affected by temperature was revealed.

Mechanical Behavior Assessment of Ti-6Al-4V ELI Alloy Produced by Laser Powder Bed Fusion

The present work correlates the quasi-static, tensile mechanical properties of additively manufactured Ti-6Al-4V extra low interstitial (ELI, Grade 23) alloy to the phase constituents, microstructure, and fracture surface characteristics that changed with post-heat treatment of stress relief (670 °C for 5 h) and hot isostatic pressing (HIP with 100 MPa at 920 °C for 2 h under an Ar atmosphere). Ti-6Al-4V ELI alloy tensile specimens in both the horizontal (i.e., X and Y) and vertical (Z) directions were produced by the laser powder bed fusion (LPBF) technique. Higher yield strength (1141 MPa), higher tensile strength (1190 MPa), but lower elongation at fracture (6.9%), along with mechanical anisotropy were observed for as-stress-relieved (ASR) samples. However, after HIP, consistent and isotropic mechanical behaviors were observed with a slight reduction in yield strength (928 MPa) and tensile strength (1003 MPa), but with a significant improvement in elongation at fracture (16.1%). Phase constituents of acicular α′ phase in ASR and lamellar α + β phases in HIP samples were observed and quantified to corroborate the reduction in strength and increase in ductility. The anisotropic variation in elongation at fracture observed for the ASR samples, particularly built in the build (Z) direction, was related to the presence of “keyhole” porosity.

Research on high-temperature mechanical properties of wellhead and downhole tool steel in offshore multi-round thermal recovery

Abstract High-temperature tensile tests at 25, 150, 250, and 350°C were carried out on 30CrMo, 42CrMo, 1Cr13, and 304 steels. The changes in tensile strength, yield strength, elongation, and area reduction ratio with temperature were determined. By analyzing the fracture morphology and the relationship between strength and hardness, the influence of high-temperature mechanical properties on crack sensitivity and the mechanism of crack formation is discussed. Experimental results indicated that both the tensile and yield strengths of the four steels gradually decrease with the increase in temperature. The yield ratios of 30CrMo, 42CrMo, 1Cr13, and 304 steels are, respectively, 0.71–0.77, 0.79–0.86, 0.84–0.88, and 0.33–0.40 which shows that among the four steels, 304 has the best ductility, while 1Cr13 has the worst ductility. As for the four steels, the values of reduction ratio of area are greater than 60%, except for 42CrMo which is slightly lower than 60% at 150 and 250°C, indicating that the four steels have low crack sensitivity within the test temperature range. Ductile fracture is the main fracture mechanism for 30CrMo, 42CrMo, and 304 steel, whereas brittle fracture is predominant for 1Cr13. There is a linear regression relationship between the strength and hardness at different temperatures. The obtained linear regression relationship can be used to predict and estimate the strength of 30CrMo, 42CrMo, 1Cr13, and 304 steels at different temperatures according to the hardness results.

A novel vulnerability model considering synergistic effect of fire and overpressure in chemical processing facilities

Processing facilities are faced with spatial-temporal dependent multiple-hazards. These hazards could cause catastrophic consequences. A novel vulnerability model called the “fire and explosion synergistic effect model” (FESEM) is proposed in the present study to model equipment vulnerability under the spatial-temporal synergistic of heat radiation and overpressure. On the basis of the fire synergistic effect model, the FESEM firstly model the temperature elevation and the yield strength reduction of the storage tank wall under fire heat radiation. Then, based on the von Mises yield criterion, the FESEM models the equivalent stress under overpressure. Combining the lowered yield strength induced by fire heat radiation and equivalent stress induced by overpressure under the synergistic effect, the logistic function is used to estimate time to failure and escalation probability. The application of the model is demonstrated in the case study, which confirms that the synergistic effect is significant and closer to reality. The parameters that have considerable effects on time to failure and escalation probability are discussed. The proposed method will serve as a rapid quantitative risk assessment tool of multi-hazard coupling, including the domino effect. The model will serve as an essential guide for preventing and controlling domino effects.