Loss Of Toughness Research Articles

Impact toughness of LPBF 316L stainless steel below room temperature

The fracture behavior of LPBF 316L stainless steel in rapid loading conditions was characterized from room to cryogenic temperatures. Instrumented impact toughness tests allow to determine the influence of the microstructural features of this material on its crack initiation and propagation behavior. In the stress-relieved, homogenized/partially recovered and recrystallized states, LPBF 316L exhibit gradual impact toughness decreases between 20 °C and – 193 °C, with close toughness loss ranging from 0.38 to 0.55 J cm−2/°C. These values were similar to those reported by the literature for hot isostatically pressed (0.35–0.58 J cm−2/°C) and wrought (0.45–0.51 J cm−2/°C) 316L stainless steels, meaning that the microstructural features of LPBF 316L (segregations cells, dislocations cells, oxide particles, etc.) did not significantly influence the temperature sensitivity of its fracture properties. Whatever the testing temperature and microstructural state, fully ductile fracture occurred by decohesion at the oxide/matrix interfaces and void growth into dimples. The martensitic transformation during deformation at low temperature did not appears to play a significant role in the temperature sensitivity of the decrease in impact toughness of these materials. The latter is likely a consequence of the loss of ductility of the austenitic matrix, especially, under localized strain conditions.

Long-term thermal aging of austenitic stainless-steel weld: Microstructure evolution in δ-ferrite and δ / γ phase boundary and apparent recovery of mechanical properties

This study aimed at investigation of thermal aging effects on evolution of microstructure and mechanical properties of ER316L austenitic stainless-steel weld (ASSW). The ASSW was subjected to thermal aging at 400 °C for up to 30,000 h. Initially, thermal aging triggered spinodal decomposition of δ-ferrite and clustering of Ni. Thermal aging up to 20,000 h further enhanced spinodal decomposition and G-phase formation. After 30,000 h of aging, precipitation of Mo-rich χ-phase occurred adjacent to the G-phase. Concurrently, thermal aging induced segregation of different elements and formation of nickel depletion zone was observed at the ferrite/austenite (δ/γ) phase boundary. The consequence of these microstructure changes was the hardening of δ-ferrite and loss of fracture toughness of ASSW. However, after 30,000 h of aging at 400 °C, degraded fracture toughness and tensile properties were partially recovered. This recovery in fracture toughness was attributed to the evolution of microchemistry and the formation of a softer shell in the δ/γ phase boundary region.

Environmentally Assisted Cracking of Duplex and Lean Duplex Stainless Steel Reinforcements in Alkaline Medium Contaminated with Chlorides

Herein, the corrosion performance of different stainless steel (SS) reinforcing bar grades in alkaline solution is presented, including UNS S32205 duplex stainless steel (DSS), UNS S32304 and UNS S32001 lean DDS (LDSS). The electrochemical dissolution kinetics were studied by potentiodynamic polarization and the Tafel slope method. The environmentally assisted cracking (EAC) mechanisms of the different SS grades in the presence of Cl− were revealed with the slow strain rate test (SSRT). The higher activation of the anodic branch and the loss of toughness were related to the austenite-to-ferrite phase ratio. UNS S32205 DSS presented the slowest anodic dissolution kinetics, mainly due to the higher austenite content compared to the other LDSS; however, it suffered a more severe EAC than the UNS S32304 LDSS. In the case of UNS S32001 LDSS, even while having the lowest Ni content (i.e., large ferrite α-phase ratio), it experienced the least decrease in elongation as well as low anodic dissolution kinetics for Cl− contents up to 8 wt.%, where the Cl− threshold was reached.

Assessing the durability performance of high belite cement incorporating fly ash under long-term temperature variations

The widespread use of ordinary Portland cement (OPC), which has a significant carbon footprint, greatly contributes to the climate crisis. High belite cement (HBC) is renowned for its low-carbon characteristics, resulting in an evident reduction in both energy consumption and CO2 emissions. Fly ash (FA), an industrial solid waste material, is commonly employed in the construction of mass concrete structures. This combination facilitates the adoption of cleaner and more ecologically sustainable construction manufacturing processes. The durability of structures constructed from HBC and FA has not been fully demonstrated due to their exposure to constantly changing atmospheric conditions. In order to unravel this issue, a comparative investigation was carried out through laboratory acceleration testing, aiming to evaluate the macro- and micro-mechanical properties, chemical compositions, and micro-morphology of HBC and OPC with FA under a rapid temperature changing cycle (RTC) within 5–45°C. The findings reveal the mechanism of deterioration under RTC, including the phase transformation of C–S–H, the propagation of micro-cracks, the coarsening of the pore structure, and the loss of toughness. FA alleviates the reduction in toughness, but also undermines the mechanical properties. Additionally, it was noted to undergo pozzolanic reaction, residual hydration and carbonation during RTC. Regarding OPC, the inclusion of FA within a specific dosage range (0–30%) has a beneficial impact on compressive strength. However, as for HBC, the presence of FA entirely exhibits a detrimental effect on service performance.

Twin and phase boundaries synergistic effect on multiscale dynamic fracture in Ni-based deformed superalloy

A multi-scale model of dynamic impact fracture of Ni-based deformed superalloy was proposed based on molecular dynamics and finite element methods, and verified by experiments to reveal the synergistic effect of twin and phase boundaries on dynamic fracture properties and behavior from nanoscale to macroscale. The results show that the synergistic effect of twin and phase boundaries can effectively suppress the unfavorable brittle propagation in the nanoscale owing to the dispersed distribution of strengthening phase-induced reduction of the stress concentration on the twin boundary. The nucleation and emission of perfect dislocations, Shockley dislocations, and Frank dislocations promote ductile propagation, while the pile-up of stair-rod dislocations induced stress concentration leads to brittle propagation. In the macroscale, the synergistic effect of twin and phase boundaries can effectively inhibit the loss of dynamic fracture toughness, and impede crack initiation and crack propagation through the reduction of Mises stress concentration and the decrease of maximum equivalent strain caused by the dispersed Ni3Al precipitates. The physical mechanism of the multi-scale crack propagation and fracture, and the influence law of dynamic fracture toughness of Ni-based deformed superalloy, can provide a guide to the failure prediction, protection, and development of aviation turbine blades.

The Effect of Direct Quenching on the Microstructure and Mechanical Properties of NiCrMo and Cu-Bearing High-Strength Steels.

In this work, two types of 590 MPa grade steels, composed of NiCrMo steel and Cu-bearing steel, were processed using traditional offline quenching and tempering and direct quenching (DQ) and tempering. The influence of DQ on microstructural evolution and strengthening mechanisms of these two types of steel was investigated. Grain refinement and dislocation density increase were determined by controlled rolling and following the DQ process in both two types of steel. In Cu-bearing steels, the refined grains and high-density dislocation further promoted the precipitation behavior of Cu-rich particles and alloyed carbides during the tempering treatment. Compared with traditionally quenched and tempered steels, NiCrMo steels after the direct quenching and tempering (DQT) process achieved 106 MPa higher yield strength through grain refinement strengthening and dislocation strengthening, while the Cu-bearing steels after the DQT process achieved 159 MPa higher yield strength through grain refinement strengthening, dislocation strengthening, and precipitation strengthening. The contribution degree of different strengthening mechanisms was quantitatively analyzed. Grain refinement also compensated for the toughness loss caused by the increase in dislocation, leading to an impact energy of 237 J and 248 J at -84 °C for NiCrMo and Cu-bearing steels after DQT, respectively.

Age-dependent changes in collagen crosslinks reduce the mechanical toughness of human meniscus.

The mechanical resilience of the knee meniscus is provided by a group of structural proteins in the extracellular matrix. Aging can alter the quantity and molecular structure of these proteins making the meniscus more susceptible to debilitating tears. In this study, we determined the effect of aging on the quantity of structural proteins and collagen crosslinks in human lateral meniscus, and examined whether the quantity of these molecules was predictive of tensile toughness (area under the stress-strain curve). Two age groups were tested: a young group under 40 and an older group over 65 years old. Using mass spectrometry, we quantified the abundance of proteins and collagen crosslinks in meniscal tissue that was adjacent tothe dumbbell-shaped specimens used to measure uniaxial tensile toughness parallel or perpendicular to the circumferential fiber orientation. We found that the enzymatic collagen crosslink deoxypyridinoline had a significant positive correlation with toughness, and reductions in the quantity of this crosslink with aging were associated with a loss of toughness in the ground substance and fibers. The non-enzymatic collagen crosslink carboxymethyl-lysine increased in quantity with aging, and these increases corresponded to reductions in ground substance toughness. For the collagenous (Types I, II, IV, VI, VIII) and non-collagenous structural proteins (elastin, decorin, biglycan, prolargin) analyzed in this study, only the quantity of collagen VIII was predictive of toughness. This study provides valuable insights on the structure-function relationships of the human meniscus, and how aging causes structural adaptations that weaken the tissue's mechanical integrity.

Investigation of toughening mechanism about core-shell morphology in bio-based polyamide ternary composites

ABSTRACT Bio-based polyamide 56 (PA56) is an environmentally friendly polymer but has not been widely used due to its inherent disadvantages of low impact strength and brittleness. In this paper, polyethylene and maleic anhydride grafted EPDM were used to co-modify PA56. The core-shell structure of PP and EPDM-g-MAH could increase the impact strength of the composites by a factor of 4.5 without significant loss of toughness. The toughness and rigidity of PA56 were balanced while the thermal stability and crystalline properties were maintained in a betterstate. This gives PA56 great potential for the automotive and construction machinery industries.

Enzyme-Mineralized PVASA Hydrogels with Combined Toughness and Strength for Bone Tissue Engineering.

Enzymatic mineralization is an advanced mineralization method that is often used to enhance the stiffness and strength of hydrogels, but often accompanied by brittle behavior. Moreover, the hydrogel systems with dense networks currently used for enzymatic mineralization are not ideal materials for bone repair applications. To address these issues, two usual bone repair hydrogels, poly(vinyl alcohol) (PVA) and sodium alginate (SA), were selected to form a double-network structure through repeated freeze-thawing and ionic cross-linking, followed by enzyme mineralization. The results demonstrated that both enzymatic mineralization and double-network structure improved the mechanical and biological properties and even exhibited synergistic effects. The mineralized PVASA hydrogels exhibited superior comprehensive mechanical properties, with a Young's modulus of 1.03 MPa, a storage modulus of 103 kPa, and an equilibrium swelling ratio of 132%. In particular, the PVASA hydrogel did not suffer toughness loss after mineralization, with a high toughness value of 1.86 MJ/m3. The prepared hydrogels also exhibited superior biocompatibility with a cell spreading area about 13 times that of mineralized PVA. It also effectively promoted cellular osteogenic differentiation in vitro and further promoted the formation of new bone in the femur defect region in vivo. Overall, the enzyme-mineralized PVASA hydrogel demonstrated combined strength and toughness and great potential for bone tissue engineering applications.

Effects of laser welding speed on the microstructure and microhardness of ultra-high strength steel S1100

Ultra-high strength steels strengthened via thermomechanical processing and low alloying constituents are currently quite popular for industrial applications. The popularity is primarily due to these steels being relatively economical compared with their high-alloy rivals, making them feasible to provide significant strength-to-weight ratios with reasonable costs in steel structures. However, welded joints in most steel structures cannot be avoided, and ultra-high strength steels, due to their thermomechanical strengthening mechanisms, are prone to loss of strength, toughness, or ductility after welding. Also, due to the ultra-high strength levels of the base metals, providing a suitable filler material with mechanical properties comparable to those of the base metals for filling the joint gap seems challenging. Accordingly, laser welding can be a relatively more suitable approach than arc welding to weld ultra-high strength steels, considering its easier control over the weld heat input, joint shape, and the possibility of welding without the requirement of filler metals. Therefore, this study investigates the influence of travel speed and its subsequent change in heat input of laser welding on the joint shape, microstructure, and hardness of the S1100 low-alloy carbon steel, one of the most commonly used ultra-high strength steels in modernized steel structures.

Role of Inorganic Fillers on the Physical Aging and Toughness Loss of PLLA/BaSO4 Composites.

The addition of inorganic fillers has been reported to increase the toughness of poly(l-lactide) (PLLA), but the effect of physical aging in such composites has been neglected. The present work discusses the effect of the still ongoing segmental relaxation in PLLA-based composites filled with BaSO4 inorganic particles in regard of the filler quantity. By means of differential scanning calorimetry, X-ray diffraction, and tensile testing of progressively aged PLLA filled with particles ranging from 0.5-10 wt %, we observed an increase in the mechanical energy required to activate the plastic flow of the primary structure in the PLLA matrix, which resulted in the embrittlement of the majority of composites upon enough aging. Results further clarify the role of debonding in the activation process of PLLA, and the behavior of the composite is described at the segmental level. Only an addition of 10% of particles has effectively preserved a ductile behavior of the samples beyond 150 aging days; therefore, we strongly remark the significance of studying the effect of physical aging in such composites.

Effects of proteases on textural softening and changes in physical property of harpiosquillid mantis shrimp (Harpiosquilla raphidea) during the iced storage

SummaryRapid softening of texture is a major problem associated with quality loss and consumer rejection of harpiosquillid mantis shrimp (Harpiosquilla raphidea) (HMS). Effects of endogenous proteases in muscles and digestive tract on protein degradation and softening were investigated. Scanning electron microscopic and histological images indicated drastic destruction of muscle during iced storage. Based on autolysis, maximal activity was found at pH 8.5 and 55 °C, and serine proteases including trypsin were dominant. Cathepsin B and L + B in muscle were altered throughout storage, while trypsin remained constant in HMS meat for 1–3 days. Firmness and toughness decreased and coincided with augmented degradation of myofibrillar proteins and collagen. Trypsin from the digestive tract was contaminated into the abdomen during iced storage, therefore inducing drastic hydrolysis of muscle proteins. This phenomenon caused the undesirable pasty/mushy texture associated with the loss in firmness and toughness of meat within 3 days of storage.

Enhancement of strength-ductility trade-off in a 2000 MPa grade press-hardened steel via refined martensite with stable high-density cementite

High-strength press-hardened steels (PHSs) are characterized by a martensite structure of high strength and adequate ductility. Strengthening PHSs with high C contents is usually accompanied by a loss of ductility and toughness. To overcome this inherent strength–ductility trade-off dilemma, we propose a novel strategy to achieve outstanding mechanical performance by introducing stable high-density Cr-rich cementite, which refines the martensite structure via Zenner pinning effect in a novel 2000 MPa grade PHS. Specifically, a high tensile strength of 2085 MPa with an appreciable total elongation of 10.1% is achieved in the novel PHS, which is far superior to commercial 22MnB5 steel (1519 MPa and 10%). The strength increase is predominantly induced by a high density of dislocations and cementite in the novel PHS, while the good ductility is attributed to the refined martensite structure coordinating plastic deformation and the enhanced work-hardening ability and dislocation storage capability mediated by massive cementite. The work can lay foundations for designing high-strength PHSs with good ductility.

The effect of vanadium micro-alloying on the microstructure of welded joints in high-strength structural steels

The balance between high strength and toughness in high-strength-low-alloy (HSLA) steels can be defined by the thermal cycles in the heat-affected zone (HAZ) of a welded joint, during a double-pass welding process with secondary heating in the inter-critical zone (IC CG HAZ). After multiple heating cycles in the temperature range between Ac1 and Ac3, the steel undergoes a strong loss of toughness and resistance to fatigue, mainly caused by the formation of residual austenite (RA). This study aims to investigate the influence of vanadium addition on the behavior of IC GC HAZ in S355-grade HSLA steel. The welding thermal cycles were simulated, considering five different inter-critical temperatures, between 720 and 790 °C. The addition of vanadium as a micro-alloy to an S355 structural steel was found to increase the mechanical strength of the IC GC HAZ zone of a welded joint without compromising toughness and fatigue resistance. This result is obtained through the generation of a bainitic microstructure with dispersion of fine regions of residual austenite and a fine and uniformly distributed precipitation.Graphical abstract

Influence of Fabrication Route and Copper Content on Nature and Kinetics of 475 °C‐ Embrittlement in Cu‐Containing Super Duplex Stainless Steels

The influence of hot‐rolling, hot isostatic pressing (HIP), welding, as well as copper content on 475 °C‐embrittlement is studied in super duplex stainless steels. The as‐received samples are solution annealed and quenched. Then, to study the kinetics and nature of phase transformations during fabrication, the samples are aged for a very short duration of 5 min at 475 °C. Atom probe tomography results reveal that the processes involving more plastic deformation such as hot rolling and HIP accelerate chromium and iron phase separation and cause precipitation of copper‐rich particles (CRPs) in ferrite, resulting in significant toughness loss. In contrast, the weld does not show a high level of chromium and iron phase separation or CRPs precipitation, preserving its toughness after the short aging. The experiment and the inverse interdiffusion calculations reveal that raising the copper content slow down chromium and iron phase separation but significantly increase the CRP number density and decrease the toughness of the HIPed material. Precipitation simulation of CPRs show that the model must be modified based on each processing condition. It is concluded that hot rolling and HIP accelerate 475 °C‐embrittlement, which cannot be prevented by raising the copper content.

Experimental study on fracture and acoustic emission properties of internally cured concrete with super absorbent polymer subjected to high temperature

The three-point bending experiment was conducted on notched beams containing five different SAP contents to investigate the influence of high temperature on the fracture performance of Superabsorbent Polymer (SAP) concrete. Acoustic Emission (AE) technology was employed to monitor real-time crack propagation, and scanning electron microscopy (SEM) was utilized to analyze the micro-pore structure. The experimental results reveal the following findings. After exposure to high temperatures, the peak strength of SAP concrete continuously decreases. Compared to specimens at 20 °C, the strength loss after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 55%, and 87%, respectively. However, the introduction of SAP can reduce the proportion of strength loss in the concrete. Additionally, SAP improves the toughness of the concrete, with an increase in ductility coefficient ranging from 4.0 to 6.8 times as the loading temperature increases. Similar to the strength variation pattern, the initial fracture toughness of SAP concrete exhibits a significant decrease with increasing heating temperature. The loss in initiation toughness after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 42%, and 85%, respectively, while the loss in unstable fracture toughness is 11%, 46%, and 74%. Based on the experimental results, this study proposes two temperature-dependent fitting models for the peak strength and fracture toughness of SAP concrete, which are compared and validated with the experimental results. SEM analysis reveals a loose and porous internal structure in SAP concrete. Through the analysis of AE signals at different temperatures, the fracture process is elucidated based on the b-value method. Moreover, RA-AF analysis indicates that an increase in temperature reduces the proportion of tensile-type cracks in specimens with the same SAP content. From the temperature loaded results spanning 20 °C–600 °C, the proportion of tensile cracks decreases from 80% to 50%, indicating a transition in the failure mode from tension to shear. However, this trend is not significantly affected by the temperature increase, suggesting that the failure mode of the specimens is primarily determined by the internal pore structure of the concrete rather than the temperature load. The research findings provide experimental evidence for the application of SAP concrete in engineering projects.

Enhanced mechanical properties of a Fe-Mn-Al-C austenitic low-density steel by increasing hot-rolling reduction

The microstructure evolution and mechanical properties of a Fe-Mn-Al-C austenitic low-density steel at different hot-rolling reductions have been investigated. It was found that with the increase in hot-rolling reduction from 45% to 82%, the grain size was uniformly refined and the dislocation density was continuously increased. As a result, both yield strength and ultimate tensile strength were effectively enhanced while the ductility and toughness only slightly decreased. An excellent combination of yield strength, ultimate tensile strength, total elongation, and toughness of 648 MPa, 976 MPa, 50%, and 105 J/m2, respectively, was obtained. The yield strength increment was interpreted by the stronger grain boundary strengthening and dislocation strengthening, and the minor loss of ductility and toughness was arising from the faster saturation of the slip band refinement (slip band spacing reached ∼50 nm) and an earlier occurrence of microbands due to the finer grain size. Based on this research, it is proposed that increasing the hot-rolling reduction was an effective approach to enhance the overall mechanical properties of the low-density steel with a fully austenitic microstructure.

Highly wear-resistant and recyclable paper-based self-lubricating material based on lignin-cellulose-graphene layered interwoven structure

Conventional paper-based wear-resistant materials employ thermosetting resin as the matrix, which are difficult to recycle, degrade, and reuse after scrapping, causing significant damage to the environment. The discovery of sustainable alternatives has the potential to transform the manufacture of paper-based wear-resistant materials into low-carbon production. Herein, inspired by spider webs sticking to insects, a paper-based self-lubricating material based on lignin-cellulose-graphene layered interwoven structure was prepared by lignin-cellulose assisted in-situ exfoliation of flake graphite strategy. Graphene adheres to the interlaced cellulose network, while lignin serves as a natural binder and matrix, resulting in a 2D interwoven structure. The paper-based film had a 37.4% greater average mechanical strength than pure lignin-cellulose film and a 56% lower toughness loss following heat treatment. The friction coefficient of the film-15% was 173.3% lower than that of the film-10%, and it maintained long-term stability with a low wear rate of 3.9 × 10−3 mm3/(N·m). Furthermore, the end-of-life products were recycled five times and can be degraded by microorganisms in moist soil within 40 days. The degradation products can provide nutrients for plant growth, indicating that it is a potential alternative to non-recyclable wear-resistant materials for light-duty transmission machinery.

Atmospheric corrosion and impact toughness of steels: Case study in steels with and without galvanizing, exposed for 3 years in Rapa Nui Island

We studied atmospheric corrosion on Rapa Nui Island, using galvanized and non-galvanized SAE 1020 steel samples exposed on racks. We also added Charpy samples of both materials to directly determine the effect of corrosion rate on these materials' impact toughness. The results indicated a correlation between corrosion rate and toughness loss in the studied materials. In the corrosion study, we could also demonstrate the effect from increased insular population growth on contaminants which aid atmospheric corrosivity. Results showed that atmospheric SO2 has tripled compared with similar corrosion studies done 20 years ago (Mapa Iberoamericano de Corrosión, MICAT), increasing corrosion rates. Our results show how human factors can influence changes in environmental variables that strengthen corrosion.

Rapid tempering of a medium-carbon martensitic steel: In-depth exploration of the microstructure – mechanical property evolution

Rapid tempering is a remarkable sustainable and energy-efficient way to modify properties of as-quenched martensite, particularly its toughness and ductility. In this work, tensile and fracture toughness properties, and microstructural evolution of a medium-carbon (0.4 wt%), low-alloy steel under different rapid tempering circumstances are discussed. The hot-rolled and direct-quenched specimens were subjected to rapid tempering treatments (heating rate of about 90 °C/s) to the different tempering temperatures (320–720 °C). As a reference material, one sample was subjected to conventional tempering at 420 °C for one hour. The results indicated that the mechanical properties and microstructural features are influenced considerably by tempering temperature rather than the holding time. Despite the short tempering duration, the strength of tempered martensite dropped (from a max. tensile strength of ∼ 2100 MPa to a min. of ∼ 1100 MPa) while ductility increased with increasing tempering temperature (from a tensile elongation of 4% to ∼ 15%). However, the rapidly tempered sample at 420 °C experienced a loss of fracture toughness as a result of coarse stick-like cementite precipitation. Microstructural observations revealed that, even with a short time frame, tempering temperature plays a significant role in the resulting cementite morphology. At lower tempering temperatures, the cementite precipitates have a stick-like structure, while at higher temperatures, they become more globular/spheroid-like. This change in cementite morphology led to an enhancement in fracture toughness. Overall, the results indicated that, by a proper design of the rapid tempering process, an excellent combination of tensile properties and fracture toughness can be obtained compared to conventional tempering while significantly saving time and energy.