Tensile Properties Research Articles

Effect of Rare Earth Ce on Structure and Properties in 7CrSiMnMoV Die Steel Castings

In this study, rare earth (RE) Ce is used to modify the interaction between atoms in 7CrSiMnMoV die steel castings. The tensile properties are performed, and strengthening mechanism are analyzed by investigated fracture surface, and microstructure by optical microscopy (OM) and scanning electron microscope‐energy dispersive spectrometer (SEM‐EDS). And ab initio molecular dynamics (AIMD) is used to simulate the effect of the Ce element on the local atomic structure of the FeCeC system alloy steel. The results indicate the strength can increase from 722.55 to 1074.27 MPa, and the elongation can increase from 24.86% to 44.22% with a RE Ce concentration of 0.009%. It is attributed to that doping of Ce can inhibit the formation of network eutectic cementite, refine the lamellar spacing of pearlite, and even form granular cementite and martensite structures. AIMD simulation results show that C atoms tend to be surrounded by Fe, and the strong chemical bonds of FeC make the Fe‐centered C more stable with an increase in RE Ce concentration. And doping Ce can introduce new local topological and chemical orderings such that the FeCFe triplets predominantly form small and big angles shifting from near 75° and 136° to 47° and 81°, respectively.

Insight into performance and lifetime of ecofriendly pollution barriers in landfill for emergency: A thermogravimetric analysis for novel polymer materials

The novel polymer barrier wall is an in-situ remediation technology designed to effectively control the migration of pollution and prevent the diffusion of pollutants by blocking, sealing, or altering the direction of groundwater flow. With its advantages of rapid chemical reaction (achieving 95 % strength within 15 min) and portable equipment suitable for narrow and rugged emergency sites, this innovative polymer barrier demonstrates promising prospects for practical application. Hence, ensuring the long-term durability of new materials under corrosive and high-temperature leachate conditions is crucial. In this study, a comprehensive investigation was conducted on the corrosion and thermal aging performance of novel polymer materials. Firstly, the mechanical tensile properties of the polymer materials were examined after immersion in leachates, aiming to elucidate the degradation mechanism underlying these properties. Subsequently, thermogravimetric (TG) analysis was performed on the polymer materials immersed in various leachates. And the thermal stability and oxidation stability of novel materials were investigated using a thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer (TG-FTIR). Based on the results obtained from thermal analysis, the service life of polymer materials under different pollutants was ultimately predicted utilizing the Arrhenius model. The findings indicate that the novel polymer materials exhibit commendable durability and pose little risk of causing secondary pollution.

Sustainable and mechanical properties of Engineered Cementitious Composites with biochar: Integrating micro- and macro-mechanical insight

Engineered Cementitious Composites (ECC) are ductile, strain-hardening cementitious composites with a tightly controlled crack opening profile. A significant concern in the development and application of ECC is its high carbon emissions associated with high cement content consumption. As an emerging green additive, biochar can significantly cut down on the carbon emission of concrete products. However, research that integrates micro- and macro-mechanical insights with biochar incorporation is limited. In this study, micro-mechanical tools indicated that a certain amount of substitution biochar could enhance the tensile properties of ECC. The study assessed various properties including compressive strength, porosity, density, tensile performance, crack pattern, sustainability and cost of ECC with different biochar proportions. The findings showed that incorporating 10 %–20 % biochar effectively increased the tensile strain capacity and decreased the crack opening width in ECC materials. This improvement can be attributed to the introduction of finer biochar particles (≤75 μm) at the fiber/matrix interfacial transition zone, which alters the fiber-bridging force by reducing the chemical and frictional bond strength between the fiber and matrix, as revealed by micro-mechanical tests and microstructural inspection. Moreover, the utilization of biochar contributes to reducing the carbon emission of ECC, enhancing sustainability while maintaining a ∼10 % minimal reduction in compressive strength. Overall, this study introduces a novel approach for reusing low-carbon biomass waste in the production of building materials, offering potential advantages in micro- and macro-mechanical performance, cost-effectiveness, and environmental sustainability.

Effect of Al content on mechanical properties and corrosion performance of novel Fe-Cr-Al alloy steels in a CO2-O2 coexistence environment

The present study involved preparing five novel Fe-Cr-Al alloy steels with varying Al content based on commercially available 3Cr steel. The effect of Al content on the mechanical properties and corrosion performance in a CO2-O2 coexistence environment was investigated in novel Fe-3Cr-(0–2.5)Al alloy steels, and the microhardness, impact, and tensile properties were measured and compared. The corrosion rate, corrosion product film, and corrosion mechanism were studied using a weight-loss method, microscopic characterization, and electrochemical tests. The results showed that the tensile and impact properties of Fe-Cr-Al alloy steels exhibited a decreasing trend with increasing Al content. No localized corrosion was observed at an Al content of 2 wt%, attributed to the formation of a dense amorphous corrosion product film on the material surface and pre-passivation. Among the alloy steels examined in this study, the 3Cr2Al alloy steel exhibited the most optimal balance between mechanical properties and corrosion resistance.

Formation of the Interlock Morphology and Its Role in Refill Friction Stir Spot Welding of Aluminum Alloy to Steel

Considering energy conservation and emission reductions, lightweight automobiles have become a research focus in the automotive industry. Steel/aluminum joining is regarded as an ideal lightweight structure, which can not only reduce the energy consumption but also ensure safety and is already attracting extensive attention. In this study, aluminum alloy 6061 and B410LA steel sheets were successfully joined by refill friction stir spot welding. The tensile properties, microhardness distribution and interfacial microstructure characteristics of the steel/Al welded joints were investigated. The maximum tensile load of the steel/Al joint was 4.3 kN. The mechanical properties of the steel/Al refill friction stir spot welded joint were largely determined by the bonding quality of the sleeve-plunging zone. With the stirring of the sleeve and the pin during the refill friction stir spot welding, work hardening occurred in the stir zone (SZ). The microhardness of the SZ was significantly higher than that of the steel base metal (BM) and could be detected on the steel side. The Fe-Al intermetallic compound (IMC) layer was continuously distributed at the interface of the sleeve-plunging zone, revealing good uniformity in the thickness. In particular, a hook-and-vortex-like structure formed during the refill friction stir spot welding process in the sleeve-plunging zone, producing a mechanical interlock effect at the interface. The ideal mechanical properties of the welded joint could be attributed to the good quality of the metallurgical and mechanical bonding at the interface, especially the mechanical interlock effect, thereby depending on the hook-and-vortex-like structure.

Influence of processing variables on fabrication of AA7475/B4C/Al2O3 hybrid surface composites via FSP

The motive of this research is to fabricate AA7475/B4C/Al2O3 hybrid surface composites (HSCs) using friction stir processing (FSP) for various applications in aerospace, marine, and automotive industries. The research systematically varied key processing variables, including rotational speed (900–1300 rpm), feed rate (30–60 mm/min), and reinforcement ratios (from 30% B4C and 70% Al2O3 to 70% B4C and 30% Al2O3), to optimize responses such as ultimate tensile strength (UTS), tensile elongation (TE), and microhardness (MH). A face-centered central composite design (FCCCD) of response surface methodology (RSM) was employed to develop mathematical models correlating the input parameters with the response variables. An analysis of variance (ANOVA) was conducted to assess the effects and interactions of the processing parameters on the composite properties. A validation test confirmed the reliability of these optimal conditions. ANOVA results indicated that the tool rotational speeds had the most significant effect on the tensile, ductility, and hardness properties of the HSCs. However, changes in feed rate and reinforcement ratio had minimal impact on these properties. The study identified optimal conditions for different responses: UTS of 452.62 MPa, TE of 6.89%, and MH of 168.52 HV at a rotational speed of 1300 rpm, feed rate of 45 mm/min, and a 50:50% reinforcement ratio (50% B4C and 50% Al2O3). The HSCs fabricated at 1300 rpm, 45 mm/min, and a 50:50% reinforcement ratio exhibited significant necking before failure, leading to a ductile failure mode.

Influence of Quenching and Partitioning Times on Austenite Stability and Tensile Properties of CMnAlSi Quenching and Partitioning Steel

Influence of Quenching and Partitioning Times on Austenite Stability and Tensile Properties of CMnAlSi Quenching and Partitioning Steel

Anisotropy in tensile properties of a high strength metastable β titanium alloy

High strength metastable β titanium alloys are widely employed in the aircraft industry due to their outstanding strength-to-weight ratio. While components can endure complex in-service mechanical loading, the anisotropy in tensile properties has been the subject of limited attention. In this study, its origin was investigated focusing on the role played by millimeter scale β grains as they were recently identified as a source of heterogeneous deformation. Tensile properties of Ti-10V-2Fe-3Al processed via different thermomechanical routes were assessed using multiple sampling directions. In particular, elongation values were observed to vary significantly depending on the testing direction. A combination of SEM, EBSD, µ-CT and in-situ DIC during tensile tests was employed to clarify the underlying causes of this behavior. Substantial differences in strain heterogeneity and localization were found related to features of β grains, including their crystallographic and morphologic orientations. Furthermore, multiple fracture mechanisms were observed to derive from the differences in deformation behavior, and eventually compete to trigger specimen failure. Elongation values are then determined by both the degree of strain heterogeneity and the operating fracture mechanisms. These findings provide a new understanding of the role of the microstructure in the tensile behavior of high strength metastable β titanium alloys.

Preparation and Characterization of Tensile Properties of PMMA/SiC Nanowhiskers Nanocomposite Films: Effect of Filler Loading and Silane Treatment

The preparation of nanocomposites through melt mixing was challenging as the nanofillers tend to form agglomeration. The silicon carbide nanowhiskers (SiCNWs) filled poly (methyl methacrylate) (PMMA) thin film in this study was prepared by means of solution casting. Acetone with low toxicity was used as solvent to dissolve the PMMA pellets. A coupling agent, silane was used to enhance the properties of composite films. Besides, the untreated and treated SiCNWs were filled into PMMA matrix, respectively with the filler loading varied from 0.2 to 0.8 wt%. The universal testing machine was used to investigate the tensile properties of composites. It was found out that the tensile strength of the PMMA was reduced in the presence of SiCNWs. However, the tensile strength had increased with the rise of filler loading. At 0.8 wt% of SiCNWs, the composites’ tensile strength was comparable to virgin PMMA. Meanwhile, the SiCNWs had reduced the elongation at break but increased the elastic modulus of PMMA/SiCNWs nanocomposite films. In addition, silane surface treatment on SiCNWs had improved the tensile strength and ductility but lowered the elastic modulus of the nanocomposites. The improvement was due to the enhancement of interfacial adhesion between SiCNWs and PMMA.

Mechanical Properties and Fatigue Life Evaluation under High Temperature and Shot Peening Application using AA7001

In some applications, AA7001 may be subjected to high temperature and fatigue. This interaction leads to varying the mechanical and fatigue properties of the above alloy. This work deals with the effects of tensile properties and constant fatigue amplitude performance. Aluminum alloys have a low specific strength, are simple to produce, and are lightweight, which has made them popular in the construction, automotive, marine, and aviation industries. The history of stress and temperature applied to the component has a significant impact on the time-dependent process of creep and strain damage. The purpose of this research is to investigate the behavior of AA7001-T6 when two phenomena, high temperatures creep and fatigue, are combined. Compared to the fatigue life interaction employing shot peening thereby, the fatigue lifetimes were The influence of shot peening on the mechanical and fatigue characteristics of AA7001-T6 was investigated utilizing four different temperatures, including RT, SP+RT, 330°C, and SP+330°C. It has been observed The application of 330°C to the tensile process lowered the ultimate tensile strength of UTS and YS by 21.9 % and 22.3 %, respectively. Shot peening improved the aforesaid percentage, lowering it to 19.2 % and 19.7%, respectively. At a stress level of 400MPa, fatigue life was lowered by 18.18 % owing to an increased temperature of 330°C, and this percentage was reduced to 10.16 % due to creating the compressive residual stresses (CRS) (SP). At (RT), the fatigue strength (endurance fatigue limit) was 229 MPa, but after Shot Peening, it improved to 237 MPa. At 330°C, shot peening increased the improved fatigue limit from 217MPa to 229MPa, resulting in a 5.24 % improvement.

Effects of Stretch-Bending Straightening on the Tensile Properties of Cold Rolled Packaging Steel

Achieving perfect flatness, tension-free surfaces, and exceptional resistance to spring back are important characteristics of packaging steel, setting the standard for high-quality material performance. To guarantee these crucial parameters, the implementation of the stretch-bending process at the final stage of the production route is indispensable. Besides improving the flatness properties, the induced plastic deformation results in an accompanying change in the mechanical properties. This investigation focuses on understanding this change in mechanical properties due to different stretch-bending straightening process parameters. A multivariate predictive model is created to calculate a process window for achieving the desired flatness and also mechanical properties in the production of packaging steel. This model is validated by experiments with a laboratory facility.

Microstructural Anisotropy, Mechanical Properties, and Fatigue Crack Growth Behavior of AA2050‐T84 Alloy

ABSTRACTThis study focuses on characterizing the microstructure and mechanical properties of AA2050‐T84 alloy produced in two different thicknesses, 20 and 130 mm. A comparative analysis between the two thicknesses aims to understand how the rolling operation for achieving thin plates influences the alloy's microstructure and overall mechanical performance. Microstructural analyses showed a highly anisotropic grain structure and preferred crystallographic orientation in the 20‐mm‐thick plate, causing anisotropic tensile properties. Also, a significant fatigue crack deviation was observed for the 20‐mm‐thick plate during fatigue crack growth tests due to its microstructure. This result was attributed to the microcrack formations perpendicular to the crack growth direction and slip bands at the intermediate ΔK, when the loading was parallel to the rolling direction. The findings from this study offer critical insights into how the rolling operation for achieving thin plates influences the microstructure and overall performance of the alloy.

Preparation of PAMgA/GL/GO antifreeze conductive hydrogel for wearable strain sensor based on physically cross-linked network

Conductive hydrogels have promising prospects in wearable strain sensor applications. However, the complex and diverse application scenarios put forward higher requirements on the conductivity, anti-freezing, tensile, self-healing, adhesion, and moisture retention properties of the conductive hydrogel. In this study, a polymagnesium acrylate/glycerol/graphene oxide (PAMgA/GL/GO) conductive hydrogel is prepared by free radical polymerization method, with magnesium acrylate (AMgA) as the polymer monomer, glycerol (GL) as the antifreeze filler, and graphene oxide (GO) as the conductive filler. Adding GL not only enhances the antifreeze properties of the composite hydrogels but also improves the moisture retention. The addition of GO increases the conductivity and the gauge factor (GF) of the composite hydrogels. When the GO content is 0.6 wt.%, the PAMgA/GL/GO conductive hydrogel demonstrates excellent properties of antifreeze, conductivity, self-healing, adhesion, and sensitivity. These excellent properties make it suitable as a wearable strain sensor for accurately monitoring human joint movements and subtle physiological signals.

Investigating the Anisotropic Mechanical Behaviour of Steel Fibre-Reinforced Aluminium-Base Composites

Base metals are often reinforced with fibres to improve their mechanical behaviour; however, it is imperative to decide the range of fibres orientation that would yield favourable strength. In this work, using sand casting method, aluminium is reinforced with galvanized steel fibres at different orientations with the aim of investigating the anisotropic mechanical behaviour of the composites. The fibre orientations considered are 0°, 30°, 60° and 90°; while the mechanical properties evaluated are impact energy, tensile, compressive and fatigue properties. Unreinforced aluminium exhibits impact energy, elongation-at-fracture, ultimate tensile strength, and maximum compressive strength of 5.15 J, 15.88%, 72.56 MN/m2, and 231.13 MN/m2, respectively. With deviation of composite fibre orientation from 0° to 30°, 60° and 90°, impact energy decreases from 8.68 to 5.56, 4.75 and 4.61 J; elongation-at-fracture decreases from 24.58 to 17.91, 12.20 and 11.87%; ultimate tensile strength decreases from 132.70 to 89.17, 63.67 and 60.34 MN/m2; and maximum compressive strength decreases from 310.66 to 251.06, 226.91 and 209.93 MN/m2. At fatigue stress amplitude of 850 MN/m2, the fatigue life of unreinforced specimen is 26 numbers of cycles-to-failure; while the deviation of composite fibre orientation from 0° to 30°, 60° and 90° yielded reduction in fatigue life from 64 to 36, 20 and 14 numbers of cycles-to-failure. Also, reduction in fatigue stress amplitude was found to increase the fatigue life of the specimens. The fatigue limit (or endurance limit) of unreinforeced specimen, and composite specimen having 0°, 30°, 60° and 90° fibre orientations are found to be 40, 70, 45, 35 and 25 MN/m2, respectively; and the corresponding fatigue life are observed to be 35480, 199518, 112195, 10021 and 5297 numbers of cycles-to-failure, respectively. The findings in this work show that specimens with 0° fibre orientation have the highest endurance of deformation before fracture, followed by specimens with 30° fibre orientation, unreinforced specimens, specimens with 60° fibre orientation and specimens with 90° fibre orientation. This could be attributed to the fact that 0° fibre orientation offers continuous reinforcement spanning the longitudinal axis of the specimens, while fibre orientation from 30° to 90° offer areas of different degrees of shear stress concentration at fibre-matrix contacts aiding fibre-matrix debonding and crack propagation. In conclusion, this work shows that orientation of steel fibre reinforcement in aluminium matrix could be varied to achieve ranges of mechanical properties and performance needed for different practical applications.

The influence of different vacancies on Zr(0001)/SiC close-packed interface performance: A first-principles study

The first-principles were employed to investigate the structure, adhesion, and tensile properties of the Zr(0001)/SiC close-packed interface with different vacancies. From the perspective of vacancy formation energy, SiC coating is beneficial for enhancing the irradiation resistance of Zr cladding. When vacancies are present, except for the Zr2 and Zr3 vacancies, introducing other vacancies reduces the stability of Zr/SiC interfaces. The C-terminated interface is more stable than the Si-terminated interface. Through electronic structure analysis, vacancies at the interface primarily reduce the bonds between Zr and SiC, decreasing the interface stability. Vacancies on the side of SiC indirectly alter the strength or quantity of covalent (bonding or anti-bonding) and ionic bonds at the interface, thus intricately lowering the interface stability. In tensile tests, the cleavage of all interfaces with vacancies still occurs on the side of Zr. Vacancies on the SiC side partly lead to increased electrons between Zr1-Zr2 or Zr2-Zr3, strengthening the metallic bonds and enhancing the interface's ideal strength and ductility. The present study offers a novel perspective from the standpoint of bonding mechanisms, providing good insights into the effects of different vacancies on the performance of Zr/SiC interfaces.

Microstructural Evolution and High‐Temperature Tensile Properties of 15Cr‐Reduced Activation Ferritic Steel Processed by Hot Powder Forging of Mechanically Alloyed Powders

Reduced activation ferritic steels are being explored as possible cladding tube materials for nuclear reactors because of their low activation and excellent irradiation resistance. In the current investigation, reduced activation ferritic steel (Fe–15Cr–2W) is processed by mechanical alloying of elemental powders followed by hot powder forging. Mechanical alloying is carried out in a Simoloyer attritor mill (Zoz GmbH), after which the powders are placed in a mild steel can and forged at 1200 °C in H2 atmosphere. X‐ray diffraction and transmission electron microscopy (TEM) investigation reveal that 10 h of mechanical alloying is required to achieve complete dissolution of Cr and W in the Fe matrix powder. The relative density and hardness distribution of the forged slab is evaluated in longitudinal as well as transverse direction to optimize the powder forging operation. Electron backscatter diffraction analysis showed dynamic recrystallization to take place during the course of hot powder forging. Tensile tests are performed at room temperature as well as at elevated temperatures (600 and 700 °C). The yield strength and ultimate tensile strength at room temperature as well as at elevated temperatures are found to be higher than those reported in literature for reduced activation ferritic steels consolidated by other techniques.

Comparative study of blending techniques in polylactic acid/cellulose nanofibrils green composites for benchtop 3D printing filaments

AbstractAdditive manufacturing for polylactic acid (PLA) reinforced with cellulose nanofibrils (CNF) could unlock fabrication of specialized and user‐specific biomedical devices. However, the process of combining PLA and CNF is challenging and proves complicated with possible irreversible CNF agglomeration and organic solvents leftover, particularly when involving solvent‐casting technique. Direct melt‐blending can mitigate these issues, but there are few reports of a single‐step melting and extrusion process to produce ready‐to‐use 3D printing filaments. This study compares the distribution of CNF fillers within the PLA matrix in PLA/CNF composites made by direct melt‐blending into filaments using a benchtop filament maker, and by solvent‐casting followed by extrusion into filaments. The filaments were 3D‐printed via fused deposition modeling (FDM), followed by tensile testing, morphology, and other characterizations. Uneven filament diameters were observed for the composite filaments prepared via solvent‐casting because of severe agglomeration, resulted in poor printability and tensile properties of filaments and 3D‐printed samples. Direct melt‐blended filament diameters were consistent, resulted in only slight decrease of tensile properties compared to pure PLA, contributing to the highest maximum tensile strength of 3D‐printed sample of 51.47 ± 1.73 MPa at 5% CNF loading. Morphology revealed good integration of CNF into PLA matrix starting at 3% CNF loading. Direct melt‐blending was comparable to the conventional methods, which enables simpler PLA/CNF composite preparation especially for 3D printing.Highlights Better dispersibility achieved by direct melt‐blending than by solvent‐casting. PLA/CNF filaments produced via solvent‐casting suffered severe agglomeration. Direct melt‐blended PLA/CNF5% yielded the highest maximum tensile strength. Morphology reveals good CNF‐PLA integration starting at 3% of CNF loading. Worsened agglomeration causing increased number of voids observed at 10% CNF.

Effect of ωiso and α precipitation during aging on tensile properties and impact toughness of a metastable β type Ti alloy

Effect of ωiso and α precipitation during aging on tensile properties and impact toughness of a metastable β type Ti alloy

Marine durability of carbon black-filled polychloroprene: Effect of seawater ageing on network, tensile and fatigue properties

With the development of marine renewable energies, the durability of materials at sea is more than ever a major issue in reducing the risk of failure of offshore devices. In this aggressive environment, elastomers, and in particular polychloroprene (CR), have many applications because of their good damping and fatigue properties. However, these materials are subject to ageing in service, which leads to changes in their mechanical properties. The ageing of these materials in a marine environment has not been extensively studied, despite the need to predict components lifetimes. This paper investigates the mechanical and microstructural consequences of a carbon black-filled CR degradation when exposed to seawater. To this end, swelling, uniaxial tensile and fatigue tests are carried out on materials previously subjected to accelerated ageing in natural seawater. Particular attention is paid to understanding the physico-chemical phenomena involved, and analysing fracture and fatigue properties in relation to those of the macromolecular network.

Semi-Alicyclic Thermoplastic Polyimide Matrixes Based on Hydrogenated Pyromellitic Dianhydride and Asymmetrical 3,4′-Oxydianiline with Good Thermal Stability and Improved Optical Transparency

Thermoplastic polyimide (PI) matrixes, including PI-a (cc-34ODA) and PI-b (ct-34ODA) were prepared via the hot-pressing procedures of the resins derived from the 3,4′-oxydianiline (34ODA) and two alicyclic dianhydrides of 1S,2R,4S,5R-hydrogenated pyromellitic dianhydride (ccHPMDA) and 1R,2S,4S,5R-hydrogenated pyromellitic dianhydride (ctHPMDA), respectively. The resins exhibited thermoplastic features with good formability at higher temperatures. The afforded semi-alicyclic PI sheets exhibited enhanced properties in comparison to commercially available, wholly aromatic thermoplastic PIs, such as PI-ref1, which are derived from 3,3′,4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-oxydianiline (44ODA), as well as PI-ref2, which is based on pyromellitic dianhydride (PMDA) and 4,4′-bis(3-aminophenoxy)biphenyl (mBAPB). In addition, the developed PI sheets exhibited high heat deflection temperatures (HDT) of 267.4 °C for PI-a and 268.6 °C for PI-b. There values were significantly higher when compared with those of PI-ref1 (Ratem® YS20, HDT: 239.0 °C), PI-ref2 (Aurum® PL450C, HDT: 238.0 °C), PI-ref3 (Ultem® 1000, HDT: 206.0 °C), PI-ref4 (Therplim® TO65, HDT: 180.0 °C), and PI-ref5 based on phthalic anhydride-terminated fluorinated PIs (HDT: 215.0 °C). In terms of mechanical properties, the current PI sheets showed superior flexural properties among the polymers with the flexural strength of 189.0 ± 11.7 MPa (PI-a) and 200.5 ± 4.2 MPa (PI-b), respectively. In addition, the PI sheets exhibited comparable compression properties, inferior impact strength, and tensile properties compared with the referenced PI counterparts. Basically, the PI-b sheet showed better comprehensive properties than those of the stereoisomeric PI-a analog.