Increase In Impact Toughness Research Articles

Effect of reinforcement parameters on the impact resistance of cementitious composites for vehicle restraint systems

The presented study investigates the dynamic resistance of cement-based large-format elements with various types of reinforcement and retrofitting. Both inner and outer reinforcement has been assessed. The effect of matrix type (low, high, and ultra-high-strength), amount of steel fibres, and ribbed reinforcing steel on impact toughness has been evaluated. The influence of an additional polymer-based layer to increase impact resistance level has also been investigated. The effectiveness of each reinforcing method has been compared. An large-scale impact hammer device KYV-I-2020 (up to 1100 J) has been used to determine the impact toughness. The results show that ribbed reinforcing steel increases the impact toughness more effectively than the fibre reinforcement, steel mesh and additional polymer layer. However, fibers significantly reduce fragmentation, especially at a higher concentration of 2.5 vol%, contributing to the overall higher impact resistance of the elements and their safety in practical use. The test results also show a significant effect of the matrix type, with the most increased impact toughness achieved when using a high strength matrix. The addition of an antifragmentation polymer layer then provides a further increase in impact toughness. The results also indicate that similar resistance capacity can be achieved using different reinforcement combinations, which is crucial for designing the material composition with the optimal performance/cost ratio. The presented research is a part of the development process of the restraint systems for stopping trucks. The data obtained has been used to create the elements with suitable composition; their effectiveness has been successfully verified by numerical simulations and real tests.

Effects of austempering time on the microstructure and properties of austempered ductile iron

The effects of austempering time on the structure and properties of high-strength austempered ductile iron were studied by using optical microscopy (OM), X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results show that the matrix structure of austempered ductile iron (ADI) consists of acicular ferrite and retained austenite. With the increase of austempering time, the content of acicular ferrite increases and the content of retained austenite first increases and then decreases, which results in tensile strength, elongation and impact toughness increase whereas hardness and wear resistance decreases. The fracture characteristics of the ADI specimens change from brittle fracture to ductile fracture with the increase of austempering time. ADI has excellent comprehensive mechanical properties after austenitizing at 900 °C for 90 min and then austempering at 250 °C for 120 min.

Effect of the Thermo-Mechanical Processing on the Impact Toughness of a 12% Cr Martensitic Steel with Co, Cu, W, Mo and Ta Doping

This paper presents the results of an experimental investigation of a 12% Cr steel where a significant increase in Charpy impact toughness and a slight decrease in ductile-brittle transition temperature (DBTT) from 70 °C to 65 °C were obtained through thermo-mechanical processing, including interim hot forging at 1050 °C with long-term annealing at 1000 °C, as compared with conventional heat treatment. At lower temperatures ranging from −20 °C to 25 °C, the value of impact toughness comprised ~40 J cm−2 in the present 12% Cr steel subjected to thermo-mechanical processing. The amount of δ-ferrite decreased to 3.8%, whereas the size of prior austenite grains did not change and comprised about 40–50 μm. The boundaries between δ-ferrite and martensitic laths were decorated by continuous chains of Cr- and W-rich carbides. M23C6 carbides also precipitated along the boundaries of prior austenite grains, packets, blocks and martensitic laths. Thermo-mechanical processing increased the mean size of M23C6 carbides and decreased their number particle densities along the lath boundaries. Moreover, the precipitation of a high number of non-equilibrium V-rich MX particles was induced by hot forging and long-term normalizing at 1000 °C for 24 h.

Investigation of the microstructure and mechanical properties of the laser welded joint of P22 and P91 steel

The present manuscript investigates the microstructural aspects and mechanical properties of laser beam welded ASTM A335 Grade P91 and P22 steel joint for power plant applications. Detailed microstructure characterization of the weld metal (WM) and heat-affected zone (HAZ) were carried out in as-welded and post-weld heat treatment (PWHT) conditions. A variation in microstructure was observed along the welded joint. This resulted in inhomogeneity in mechanical properties. The PWHT resulted in the formation of the stabilized microstructure in weldments and reduced heterogeneity in mechanical properties along the weldments. Tensile strength of weld joint in as-welded (AW) and PWHT condition was found slightly higher (617 MPa and 628 MPa, respectively) than the tensile strength of P22 steel (610 MPa). The fracture location for both AW and PWHT was observed in the P22 base region, which indicates that welded joint is stronger than the base material. Maximum tensile strength of the WZ was found 864 MPa in the as-welded condition. The hardness of WM, P91 CGHAZ and P22 CGHAZ were found 376 HV, 420 HV and 302 HV, respectively. After the PWHT, the hardness of the WM, P91 CGHAZ, P91 ICHAZ, P22 CGHAZ and P22 ICHAZ were measured 237 HV, 264 HV, 212 HV, 208 HV and 190 HV, respectively. The reduction in hardness is attributed to the tempering reaction, which results in the formation of the tempered martensite in WM and HAZ of P91 and tempered bainite in P22 HAZ. The impact toughness of the weld metal in as-welded condition was measured 85 J, which was lower than P22 and P91 steel. PWHT resulted in a drastic increase in impact toughness of WM and it was 145 J. The impact toughness of the P22 and P91 HAZ was measured 146 J and 92 J, respectively, for AW and 168 J and 140 J, respectively, after PWHT. The optimum microstructure and mechanical properties of the dissimilar welded joint were obtained after the PWHT.

Microstructural investigation of WC reinforced Ti-6Al-4V matrix surface composite fabricated via additive friction stir processing

Additive friction stir processing (AFSP) was effectively utilized to fabricate defect-free WC reinforced surface composite on Ti-6Al-4V substrate. Uniform distribution of fragmented WC particles was achieved in the composite layer. Completely β transformed microstructure, containing lamellar α/β structure coupled with ultrafine martensite α′ was observed in stir zone of FSPed Ti-6Al-4V. The addition of WC reinforcement during AFSP has led to additional microstructure refinement; as a consequence of Zener pinning and particle stimulated nucleation caused by fragmented WC particles. More than two times improvement in hardness and wear resistance was noted in WC reinforced Ti-6Al-4V (surface composite) fabricated by AFSP compared to base metal Ti-6Al-4V. Despite a little drop in hardness value, post FSP heat treatment of WC reinforced surface composite has brought about a significant increase in impact toughness.

Tensile and Impact Toughness Properties of a Zr-Based Bulk Metallic Glass Fabricated via Laser Powder-Bed Fusion.

In the past few years, laser powder-bed fusion (LPBF) of bulk metallic glasses (BMGs) has gained significant interest because of the high heating and cooling rates inherent to the process, providing the means to bypass the crystallization threshold. In this study, (for the first time) the tensile and Charpy impact toughness properties of a Zr-based BMG fabricated via LPBF were investigated. The presence of defects and lack of fusion (LoF) in the near-surface region of the samples resulted in low properties. Increasing the laser power at the borders mitigated LoF formation in the near-surface region, leading to an almost 27% increase in tensile yield strength and impact toughness. Comparatively, increasing the core laser power did not have a significant influence. It was therefore confirmed that, for BMGs like for crystalline alloys, near-surface LoFs are more detrimental than core LoFs. Although increasing the border and core laser power resulted in a higher crystallized fraction, detrimental to the mechanical properties, reducing the formation of LoF defects (confirmed using micro-computed tomography, Micro-CT) was comparatively more important.

Influence of Rubber Content on Failure Mode and Resistance Characteristics of PC/ABS Blends and their ABS Constituents under Impact

This present study has been re-established to investigate failure mode and resistance characteristics of the PC/ABS blends and their ABS constituents under impact for a range of rubber contents. This present study has still been experimentally performed under an instrumented-drop weight impact test (DWIT) at a room temperature. It has been finally revealed that with a particular size of rubber particle, content of rubber significantly influenced impact failure modes and impact resistances of the PC/ABS blends and their ABS constituents as well. The test results showed that impact strength of the blends was improved about 23.22% and 155.33% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. There was also found that an increase in impact toughness of the blends for 57.48% and 239.23% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. Whilst, impact strength of the ABS was improved about 392.98% and 190.12% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. An increase in impact toughness of the ABS for 308.20% and 172.56% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively.

Mechanical properties of UFG titanium: Notched fatigue and impact toughness

This paper focuses on the study of the impact toughness and fatigue strength with a notch of ultrafine-grained titanium Grade 4 for advanced medical implants. An ultrafine-grained structure was formed in titanium by equal-channel angular pressing according to the “Conform” scheme followed by short-term annealing. The criterion for choosing the annealing regime was the achievement of a combination of increased impact toughness and preserving of enhanced strength due to the formation of a bimodal UFG structure. Impact toughness was assessed on standard specimens with a V-notch. Fatigue tests were carried out on specimens with a stress concentrator simulating a thread in a medical device. The positive effect of finishing etching with a mixture of nitric and hydrofluoric acids, which is widely used in dental surgery for medical implants, has been revealed. It is shown that a change in the surface topography of the notch, characterized by of surface microdefects after etching, leads to an increase in the fatigue strength σ-1 by about 15% (from 180 to 220 MPa).

Correlation of Microstructure Feature with Impact Fracture Behavior in a TMCP Processed High Strength Low Alloy Construction Steel

The present article aims at elucidating the effect of thermo-mechanical controlled processing (TMCP), especially the finish cooling temperature, on microstructure and mechanical properties of high strength low alloy steels for developing superior low temperature toughness construction steel. The microstructural features were characterized by scanning electron microscope equipped with electron backscatter diffraction, and the mechanical behaviors in terms of tensile properties and impact toughness were analyzed in correlation with microstructural evolution. The results showed that the lower finish cooling temperature could lead to a considerable increase in impact toughness for this steel. A mixed microstructure was obtained by TMCP at lower finish cooling temperature, which contained much fine lath-like bainite with dot-shaped M/A constituent and less granular bainite and bainite ferrite. In this case, this steel possesses yield and ultimate tensile strengths of ~ 885 MPa and 1089 MPa, respectively, and a total elongation of ~ 15.3%, while it has a lower yield ratio of ~ 0.81. The superior impact toughness of ~ 89 J at −20 °C was obtained, and this was resulted from the multi-phase microstructure including grain refinement, preferred grain boundaries misorientation, fine lath-like bainite with dot-shaped M/A constituent.

Role of the heterogeneity in microstructure on the mechanical performance of the Autogenous Gas Tungsten Arc (GTA) welded dissimilar joint of F/M P91 and SS304L steel

The microstructure and mechanical behavior of the Gas Tungsten Arc (GTA) welded joint of ferritic/martensitic (F/M) P91 and austenitic SS304L steel was investigated in as-welded and post-weld heat treatment (PWHT) conditions. The microstructural studies included the particle size and its distribution, grain size, and percentage area fraction of the precipitates (%AFP) in different zones of the weldments. In as-welded condition, weld metal showed untempered martensitic microstructure devoid of carbide precipitates. After the PWHT, weld metal was characterized by tempered martensitic microstructure along with the decoration of the coarse carbide particles at PAGBs and fine carbonitride particles inside the matrix region. The mechanical behavior of the dissimilar weld was analyzed in as-welded and PWHT conditions by performing tensile testing, Charpy impact testing, and microhardness testing. A significant variation in microstructure and mechanical properties was obtained across the dissimilar welded joint (DWJ) for as-welded, which was minimized after the PWHT. The minimum%AFP in the coarse grain heat-affected zone was measured due to the formation of the precipitate-free soft δ ferrite patches, which also showed a negligible response to PWHT. The poor Charpy impact toughness (CIT) of 0.8 ± 1.5 J and high tensile strength of 864 ± 12.5 MPa were measured for the as-welded joint. The combination of high strength and low CIT was obtained mainly due to the untempered martensitic microstructure in the weld fusion zone. The DWJ after the PWHT showed a significant increase in Charpy impact toughness (CIT), and it was measured 70 ± 4 J. Improved mechanical behavior with a good combination of ultimate tensile strength and CIT were obtained after the PWHT.

Effects of hydrogen as a solid solution element on the deformation behavior of a near-alpha titanium alloy

The effects of hydrogen on the room-temperature mechanical properties and the deformation behavior of near-alpha alloy Ti–6Al–3Nb–2Zr–1Mo were systematically investigated. It was found that hydrogen addition increased the strength and plasticity of titanium alloy, while the impact toughness firstly increased for the sample with 65 wppm hydrogen and then decreased at higher hydrogen content. The strength was increased due to the pinning effect and the solid-solution strengthening effect of hydrogen, while the plasticity was improved by the increase of dislocation mobility and the breakage of beta laths. The increase of impact toughness at 65wppm hydrogen resulted from the enhancement of dislocation motion and multiplication, but further increasing hydrogen addition would reduce impact toughness by decreasing the cohesion strength at interfaces and grain boundaries and the breakage of beta laths. In addition, deformation behaviors of titanium alloys with different hydrogen content were discussed. Hydrogen inhibited twinning and enhanced dislocation slip to some extent. Cross-slip was hindered and planar slip was favored due to the decrease of stacking fault energy after hydrogenation. Further, basal slip and pyramidal slip were activated while prismatic slip was suppressed by hydrogen addition.

Cryogenic toughness in a low-cost austenitic steel

At low temperatures most metals show reduced ductility and impact toughness. Here, we report a compositionally lean, fine-grained Fe-30Mn-0.11C austenitic steel that breaks this rule, exhibiting an increase in strength, elongation and Charpy impact toughness with decreasing temperature. A Charpy impact energy of 453 J is achieved at liquid nitrogen temperatures, which is about four to five times that of conventional cryogenic austenitic steels. The high toughness is attributed to manganese and carbon austenite stabilizing elements, coupled with a reduction in grain size to the near-micrometer scale. Under these conditions dislocation slip and deformation twinning are the main deformation mechanisms, while embrittlement by α′- and ε-martensite transformations are inhibited. This reduces local stress and strain concentration, thereby retarding crack nucleation and prolonging work-hardening. The alloy is low-cost and can be processed by conventional production processes, making it suitable for low-temperature applications in industry.

Improvement of Impact Toughness and Abrasion Resistance of a 3C-25Cr-0.5Mo Alloy Using a Design of Experiment Statistical Technique: Microstructural Correlations after Heat Treatments

Hypoeutectic high chromium white cast irons are commonly used in the mining and cement industries, where high resistance to abrasive wear is demanded. Through the application of a Design of Experiment technique (DoE), different factors related to thermal industrial treatments are analysed with regard to resistance to abrasive wear and impact response. Abrasion tests were carried out in accordance with the ASTM G065-16 standard. The provisional results show that to increase wear resistance, high destabilisation temperatures (1050 °C) followed by slow cooling to room temperature (RT) and subsequent tempering at 400 °C are most favourable. This is because these conditions are favourable to maintaining a certain tetragonality of the martensite after tempering and also, because of the presence of a high density of mixed carbides M7C3, through a secondary precipitation during cooling. Oil quenching and a high tempering temperature (550 °C) with long dwell times of 6 h were found to increase impact toughness. These conditions favour a lack of retained austenite. The presence of retained austenite was found unfavourable for both wear resistance and toughness, whereas tempering at 400 °C has been shown to be insufficient to transform martensite on tempering, which in turn seemed to increase the hardness of the matrix constituent.

Thermal decomposition characteristics of retained austenite and its influence on impact toughness of B-containing 9Cr1Mo1Co(FB2) steel during the two-step tempering

The decomposition kinetics of retained austensite (RA) and the effect of its decomposition on the impact toughness of FB2 steel during the two-step tempering were studied by employing differential scanning calorimetry (DSC), magnetic saturation measurement (MSM) and transmission electron microscopy (TEM). Furnace-cooling from 1100 °C produces 9.7vol.% filmy RA due to the contributions to Ms from the C enrichment (MS(Che) = 102 °C) and the high internal stress (ΔMS(stress) = -93.3 °C). With the increase of the first step tempering temperature from 570 °C to 630 °C for 1–10 h, RA involves into the different decomposition characteristics, forming θ phase, M3C particles, filmy M3C and M7C3, and also leading to the volume fraction of the carbon-depleted RA transformed into martensite fγRA→M decrease from 87.6% to 0.0% during the subsequent cooling process. During the second step tempering at 670 °C, these θ and M3C particles evolve into spherical M23C6, while film-like M3C and M7C3 evolve into filmy M23(C,B)6. Deteriorated by the filmy M23(C,B)6, the impact toughness increase from 72 J/cm2 to 118 J/cm2 with the increase of fγRA→M from 0% to 87.6%. While for the samples with fγRA→M=0, enhancing the second step tempering temperature to 690 °C for 10 h can further promote the spheroidization of filmy M23(C,B)6 and reduce hardness, resulting in the enhancement of impact toughness from 72 J/cm2 to 112 J/cm2. In summary, a two-step tempering process (570 °C for 1–5 h plus 670–690 °C for 10 h) for RA-containing FB2 steel is suggested to obtain excellent impact toughness and high hardness.

A new strategy to improve viscoelasticity, crystallization and mechanical properties of polylactide

Biodegradable polylactide/masticated natural rubber (PLA/mNR) blends were prepared by electron induced reactive processing (EIReP) without using any chemical additives. The PLA/mNR blends showed droplet-matrix morphology with decreased mNR particle size after EIReP treatment. The absolute value of complex viscosity and storage modulus increased significantly for the EIReP modified blends, suggesting the improved melt strength and elasticity. The crystallization investigation showed that the cold crystallization peak of PLA phase gradually disappeared after EIReP modification. Instead, the crystallization peak arose during melt cooling process. Consequently, the crystallinity of PLA phase increased from 6.2% to 39.0% as the mNR content increased from 0 to 20 wt%. It was found that the softening temperature of PLA examined by dynamic mechanical analysis increased effectively with the characters of higher modulus compared to the non-modified blends. The EIReP modified blends exhibited excellent mechanical properties with 7-fold increase of impact toughness compared with neat PLA, implying a superior interfacial adhesion and chain interactions between the two polymer phases. Furthermore, the thermogravimetric analysis demonstrated that the thermal stability was slightly enhanced for the EIReP modified blends.

Manufacturing of Al-Li-Si3N4 metal matrix composite for weight reduction

Abstract The present analysis was aimed to identify the properties of Al 2024 composite reinforced with lithium and silicon nitride to make it applicable for automobiles, sports and aerospace applications. An effort was made to reduce the density and increase the hardness and impact properties of aluminum 2024 matrix with individual and multiple reinforcements using the double casting method under non-reactive environment. Aluminum alloy matrices with lithium, silicon nitride and the combination of both were fabricated. The microstructure, density, hardness and impact strength properties of the fabricated aluminum metal matrices were analyzed. The microstructure study reveals the uniform dispersion of reinforcements in the matrix alloy. From the results, it is understood that the hardness and impact toughness increase with the addition of silicon nitride. Density is reduced with the addition of lithium as reinforcement. When both reinforcements were added in the matrix, it was observed that there was an increase in hardness and impact strength of the composites with decrease in density of the metal matrix composite making it suitable for light weight and high strength applications.

A molecularly engineered bioderived polyphosphate for enhanced flame retardant, UV-blocking and mechanical properties of poly(lactic acid)

Polylactic acid (PLA) represents one of most promising bioplastics in response to the increasing global microplastics pollution issue facing the entire ecosystem. Nevertheless, PLA is inherently flammable and also prone to UV-light attack, significantly restricting its wide applications in packaging, fibers and electronics industry. Despite high effectiveness in PLA, existing polyphosphate-based flame retardants are usually synthesized mainly from non-degradable petrochemical compounds and their functions are limited to improving flame retardancy of the polymeric matrix. We, herein, report the synthesis of a novel multifunctional bioderived polyphosphate (PPD) for PLA by using plant-derived diphenolic acid as a starting material. Our results reveal that the addition of 6 wt% of PPD enables PLA to achieve a desirable UL-94V-0 rating and a high LOI value of 27.1% due to its high gas-phase activity, which means that the final PLA fully meets the demanding flame retardancy requirement in industry. Moreover, the resultant flame-retardant PLA shows a high ultraviolet protection factor (UPF) value of 403, which indicates its excellent UV protection capability. Because of the fine and uniform dispersion of PPD within the resin matrix and their strong interfacial interactions, the PLA/6% PPD shows a 31% increase in impact toughness and a slight improvement in tensile strength compared to the bulk PLA. This work provides a strategy to synthesize a multifunctional bio-based polyphosphate flame retardant, which holds great promise for extending the practical applications of PLA with excellent flame retardancy, UV-blocking and mechanical performances.

Low velocity flexural impact behaviors of bamboo fiber reinforced composite beams

To investigate the anti-impact behavior and loading rate sensitivity of bamboo fiber reinforced composite (BFRC) beams, low-velocity-impact flexural experiments were performed under impact velocity changing from 2 m/s to 10 m/s. Quasi-static flexural tests were carried out under the same conditions to supply a quasi-static reference to the dynamic performance. Velocity-dependent effects of the impact force, the velocity, the impulse, the displacement and the absorbed energy were revealed by the weight-dropping experiments. The impact force, the energy absorption and the impact toughness increase nearly linearly to the impact velocity. These rate sensitivities of the BFRC beam were expressed quantitively by linear fitting equations, providing a basis to design shock and explosion resistant BFRC structures.

Выбор литейных износостойких сплавов, сочетающих оптимальные показатели ударной и абразивной стойкости

This study presents the results of the selection of the most technologically and cost-effective compositions of wear-resistant Fe-C alloys for parts of industrial equipment and their production technologies. The article also considers the main types of existing wear-resistant steels and cast irons, shows their compositions and properties, describes the main advantages and disadvantages. From the point of view of economic benefits and simplicity of technology, one of the most effective for casting parts subjected to intense impact and abrasion is half nodular cast iron obtained as a result of low alloying with chromium and subsequent modification with a magnesium-containing additive. The main advantage of this alloy, which determines its high wear resistance, is that in this case, in the structure of the outer surface layer of the casting, carbon is in the form of finely dispersed carbide inclusions doped with chromium and manganese, which ensures high hardness and resistance to abrasive wear, and in the inner deep layers Castings carbon is in the form of spheroidal and vermicular graphite - this provides an increased impact toughness of the alloy.

Evaluation of pre-determined dilution of high strength steels by the Snapshot method

Dilution is an unavoidable consequence of multi-material fusion processing, i.e. welding, cladding etc. In this paper we propose a novel method for controlled dilution experiments, analyzing microstructural trends of steel filler wire diluted with steel base metal. The highlight of this method is the control of processing conditions used to melt a pre-determined dilution of two high strength steels. The materials involved are S960QL base metal machining chips and a chopped under-matched wire consumable, which is used to increase the toughness of welded joints. These materials were combined in specific mass ratios in a prepared cavity and then melted by a pulsed laser beam. A high-speed RGB camera evaluated the relative spatial temperature of the melt surface. The molten mass then solidified into a uniform nugget, confirmed by energy dispersive x-ray spectrometry (EDS) to have a homogenous chemical composition (a ‘Snapshot’ nugget). Hardness values obtained for different dilution levels were compared to a narrow gap multi-layer laser weld (NGMLW), with a decreased dilution rate yielding a decreased hardness. The Snapshot microstructures created are similar to the different regions of the NGMLW, in the weld cap and in the body of the weld. Snapshot nuggets were also evaluated for non-metallic inclusion (NMI) size distributions relating to the dilution levels (NMIs are important indicators for acicular ferrite, which has been shown to increase impact toughness).