Higher Elongation Rate Research Articles

Effect of Cerium Addition on Microstructure and Mechanical Properties of the Ductile Iron

The effect of the cerium addition on the microstructure and properties of the ductile iron is investigated. The ferrocerium is added to obtain ductile iron samples with cerium contents of 10–750 ppm. In the ductile iron with a cerium content of 60 ppm, the amount and the spheroidization rate of graphites are the highest. The tensile strength of the ductile iron is 488 MPa and the elongation rate reaches 20.17%. For the ductile iron with a high toughness demand, it is necessary to add 60 ppm Ce in the ductile iron to increase the number density and spheroidization rate of graphites. The formation of CeS inclusions effectively promotes the heterogeneous nucleation of graphites, increasing the amount of graphites. The stronger carbon diffusion during the eutectic process increases the ferrite formation in the ductile iron, leading to a lower tensile strength and a higher elongation rate. When the cerium content exceeds 460 ppm, the precipitated Ce2C3 significantly reduces the performance of the ductile iron.

Impact of Heat Treatment on the Mechanical Properties and Fracture Morphology of Ti555211 Alloy.

Heat treatment is important for optimizing the strength performance and improving the toughness of titanium alloys. In this study, we investigated the impact of three heat treatment methods (β-annealing, double annealing, and solid-solution and aging treatment) on the mechanical properties and fracture morphology of Ti555211 titanium alloy. The results show that after β-annealing treatment, the alloy retains a high strength, while showing almost no ductility, and no yield strength. The alloy after double annealing has a high elongation rate (~54%) and lower strength. After solid-solution and aging heat treatment, the alloy was able to retain both high strength and a certain degree of ductility. The optimal heat-treatment process is solid-solution treatment at 820 °C/2 h and aging at 560 °C/12 h, which results in a maximum tensile strength of 1404 MPa and an elongation rate of 11%.

Flow-induced crystallization of piezoelectric poly(L-lactide) fibers by a one-step melt-spinning process

Piezoelectric poly(L-lactide) (PLLA) fibers, exhibiting high molecular chain orientation, are promising for biomedical applications. Chain orientation decreases due to fast relaxation during melt-spinning process, which implies that a second process to induce piezoelectric chain morphology is usually necessary. This work introduces a one-step melt-spinning process of piezoelectric PLLA fibers, spun directly from the melt, employing a rheological guidance for the selection of the PLLA type and process parameters, based on Rouse's relaxation time. The chain orientation and the relaxation time increased with the optical purity and average molecular weight of PLLA. The reduction of extrusion temperature from 180 °C to 150 °C facilitated in a significant way the preservation of chain orientation, and the impact of the elongation rate was as well intensified. Combining high elongation rates of ≤ 29 s−1 and reduced extrusion temperature of 150 °C led to flow-induced crystallization of oriented crystals directly from melt in a single step. This fiber exhibited piezoelectric properties in form of a deflection of 1.9 ± 0.3 µm when applying an open-circuit voltage of 210 V. The piezoelectric response was similar to that of a fiber, melt-spun at high extrusion temperature of 180 °C, with additional post-annealing in a second step.

Low-temperature strain-sensitive sensor based on cellulose-based ionic conductive hydrogels with moldable and self-healing properties

Bioelectronics based on high-performance conductive ionic hydrogels, which can create novel technological interfaces with the human body, have attracted significant interest from both academia and industry. However, it is still a challenge to fabricate hydrogel sensor with integration of good mechanical properties, fast self-healing ability and flexible strain sensitivity below 0 °C. In this paper, we present a moldable, self-healing and adhesive cellulose-based ionic conductive hydrogel with strain-sensitivity, which was prepared by forming dual-crosslinked networks using poly(vinyl alcohol) (PVA) with borax, calcium chloride (CaCl2), zinc chloride (ZnCl2) and 2,2,6,6-tetramethylpiperidine-1-oxyl oxidized cellulose nanofibril (TCNF). The hydrogel exhibited fast self-healing within 10 s, moderate modulus of 5.13 kPa, high elongation rate of 1500 % and excellent adhesion behavior on various substrates. Due to multiple hydrogen bonding and the presence of CaCl2 and ZnCl2, the hydrogel presented a reduced freezing point as low as −41.1 °C, which enabled its application as a low-temperature strain sensor. The proposed hydrogel provides a simple and facile method for fabricating multi-functional hydrogels that can be used as suitable strain sensors for applications such as wearable electronic sensor, soft robotics and electronic skins in a wide temperature range.

Synchronous-hammer-forging-assisted wire arc additive manufacturing Al-Mg alloy

The plastic deformation-assisted wire arc additive manufacturing (WAAM) technology based on the hammer-forging method has essential application prospects in preparing high-dense fine-grain aluminum alloy components. However, the existing interlayer hammer-forging method has limitations, such as insufficient hammering force and high demand for hammering times when obtaining large plastic deformation. To effectively solve these problems, this paper proposed synchronous-hammer-forging-assisted WAAM technology and systematically studied its effects on the macroscopic morphology, microstructure, pores evolution, and mechanical properties of WAAM Al-Mg alloy specimens. The results show that under the synchronous hammer-forging (SHF) condition, a large plastic deformation of 33.97% can be achieved by the 80 N hammer forging force, and the surface flatness of the specimen was significantly improved. The grain size of the specimen was reduced from 105.92 µm in the deposited state to 37.15 µm in the hammered specimen by 64.93% with a significant equiaxed effect. Simultaneously, with the application of SHF technology and the increasing hammer-forging force, the precipitated phase dominated by Al3Mg2 was broken. The pores in the specimen changed from round to narrow and elongated shape with only 0.0065% porosity. The number of pores, equivalent diameter, and surface area were reduced by 68.33%, 13.75%, and 67.24%, respectively. The yield strength and ultimate tensile strength of the hammer-forged specimens reached 250.37 MPa and 315.03 MPa, respectively, which were 36.28% and 8.95% higher than those of the deposited specimens, and still maintained a high elongation rate of 36.11%.

Influence of PMMA brushes grafted from GO on rheological properties of PMMA/SAN immiscible blend in shear and elongation flow

In real technological processes, both shear and elongational flow is present. The material properties may differ significantly under both types of flow. Hence, they both define the final morphology and thus properties of the materials. In this work, the morphology of immiscible blends containing polymer hybrid particles was related to extensional rheological properties for the first time. The effect of various lengths of polymer brushes grafted from graphene oxide particles (GO) surface was investigated. As a polymer matrix the immiscible blend of poly(methyl methacrylate)/styrene-co-acrylonitrile (PMMA/SAN) was used. Thus the poly(methyl methacrylate) (PMMA) brushes grafted from GO (GO-g-PMMA) with various number average molar masses (Mn) of PMMA brushes with respect to chain entanglement limit of freely dispersed PMMA were prepared. The extensional rheological properties were affected by Mn of PMMA brushes, while the rheological properties in shear were unchanged. Transmission electron microscopy revealed the compatibilization effect for short densely grafted brushes with Mn of 10,300 g/mol, as smaller domains were observed. On the contrary, the higher Mn PMMA brushes facilitated coalescence. With increasing length of brushes, the elongational viscosity at low elongation rates (∼< 0.1 s−1) decreased, which facilitated the coalescence. The increase of viscosity at higher elongation rates (∼> 0.1 s−1) was not sufficient enough to cause fiber breakup and thus elongated domains were formed.

Microstructure characteristics and mechanical properties of the thin-plate AISI 430 ferritic stainless steel joints by interrupted pulsed arc welding

The feasibility of the interrupted pulsed argon arc welding (IPAW) of the 0.5 mm-thick AISI 430 ferritic stainless steel (FSS) was studied. The results showed that the sound appearances of the butt joints were obtained by the IPAW under different welding parameters. Two joining modes were obtained: (1) typical fusion pool structure with continuous coarsen columnar grain by short interrupted time and low welding speed; (2) snowflake-shape melting pool structure with relatively independent radially grew columnar grain by long interrupted time and high welding speed. The fusion zone (FZ) and heat-affected zone (HAZ) of the joints showed higher microhardness compared to the base metal because of the carbide precipitation and martensite transformation. The joint with a typical fusion pool structure fractured at the fusion zone with a low tensile strength and elongation rate because the weak bonding region between the columnar grains was perpendicular to the tensile direction. The joint with the snowflake-shaped structure displayed a high tensile strength and elongation rate, which was fractured at the BM, as a result of the randomness of the intergranular bonding interface to the tensile direction caused by dendritic radial growth.

Actin assembly requirements of the formin Fus1 to build the fusion focus.

In formin-family proteins, actin filament nucleation and elongation activities reside in the formin homology 1 (FH1) and FH2 domains, with reaction rates that vary by at least 20-fold between formins. Each cell expresses distinct formins that assemble one or several actin structures, raising the question of what confers each formin its specificity. Here, using the formin Fus1 in Schizosaccharomyces pombe, we systematically probed the importance of formin nucleation and elongation rates in vivo. Fus1 assembles the actin fusion focus, necessary for gamete fusion to form the zygote during sexual reproduction. By constructing chimeric formins with combinations of FH1 and FH2 domains previously characterized in vitro, we establish that changes in formin nucleation and elongation rates have direct consequences on fusion focus architecture, and that Fus1 native high nucleation and low elongation rates are optimal for fusion focus assembly. We further describe a point mutant in Fus1 FH2 that preserves native nucleation and elongation rates in vitro but alters function in vivo, indicating an additional FH2 domain property. Thus, rates of actin assembly are tailored for assembly of specific actin structures.

Comparison of Tensile Properties and Knot Security of Surgical Sutures: An In Vitro Mechanical Study

Studies on the mechanical properties and knot security of smaller sutures used in oral and maxillofacial surgery are limited. The objective of this study is to measure the tensile properties and knot security depending on the suture materials, knotting techniques, and number of throws using 5-0 sized sutures. Seven 5-0 sized sutures were measured in both straight-pull and knot-pull according to the procedures outlined by the United States Pharmacopeia. Regarding knot security, there were 3 predictor variables: suture material, knot technique, and number of throws. Two surgical tying techniques were square knot and surgeon's knot and the number of throws were 3, 4, and 5. One-way analysis of variance was applied to test tensile properties (α=0.05). The dichotomous outcome of knot security (stable or unstable) was analyzed using logistic regression analysis and odds ratios with Tukey-adjusted 95% confidence intervals. Ethicon polyglactin 910 was found to have the highest failure load (18.0N) of straight, while silk sutures had the lowest of both straight and knotted. A higher elongation rate was found in the 2 monofilament suture materials polypropylene and polydioxanone. Knot security depended on the suture technique, material, and number of throws. Surgeon's knots were stronger than square knots. The number of throws required to achieve knot security depends on the specific combination. For polypropylene or Jinhuan silk with the surgeon's knot, 3 throws can probably achieve knot security. The new data presented in the study provided important information for guiding the selection of smaller suture materials for oral and maxillofacial surgery. A wider range of suture combinations should be tested, and more invivo studies are needed to clarify the characteristics of sutures and knots.

LMS parameters, percentile, and Z-score growth curves for axial length in Chinese schoolchildren in Wuhan

Understanding the ocular structural changes are fundamental to defining strategies for myopia prevention and management. This study aimed to establish age-gender specific normative LMS parameters for axial length to generate percentile and Z-score growth curves in a population of Chinese schoolchildren. A total of 14,760 individuals aged 6 to 15 years from Wuhan, central China, contributed to this study. The LMS method was used for the calculation of LMS parameters and the generation of percentile and Z-score growth curves for axial length. Growth curves derived from the LMS parameters were compared with those originally calculated. Axial elongation was age- and percentile-dependent. The highest elongation rate occurred at the 98th percentile in the range 6 to 9 years, being up to 1.46 mm in boys and 1.42 mm in girls. The largest differences between original and newly generated growth curves were detected at the 98th percentile at age 15; 0.78 mm (females) and 0.63 mm (males). Multinomial logistic regression and receiver operating characteristic analyses revealed Z-scores as a good predictor for estimating high myopia development. The axial length growth curves presented in this study provide a technically solid instrument that depicts the best description of physiological eye growth for Chinese schoolchildren aged 6 to 15 years.

Force decay and discoloration of thermoplastic and thermoset orthodontic elastomeric chains

Objective: Elastomeric chains are commonly used to apply force for orthodontic dental movements. However,force decay and discoloration are two important weak points of these materials. The present study intended tocompare the force decay and color stability of different types of elastomeric chains. Material and Methods: Thisin vitro study evaluated 6 groups of elastomeric chains, including thermoplastic (TP) and thermoset (TS) chainsmade by the companies American Orthodontics (AO), Ormco (OR), and G&amp;H Orthodontics (GH). The elastomericchain forces were measured at the baseline, following 1 hour, 1 day, 1, 2, 3, 4, 5, and 6 weeks of stretching.The elongation required for the chains to exert a force of 250 g was calculated. E of each group was calculatedby a spectrophotometer following immersion in black tea solution for 6 days. Data were analyzed using theSPSS 22 software and the statistical methods of repeated measures analysis of variance and two-way analysis ofvariance (P&lt;0.05). Results: The force decay of the TS chains were significantly lower than the TP chains in the6-week study duration (P&lt;0.05), and the lowest and highest force decay was observed in the products by AOand GH, respectively. The highest force degradation occurred during the first week in all groups. The elongationrate needed for the TS chains was significantly higher than the TP chains (P&lt;0.05), and the highest elongationrate was observed in the products by OR. TS chains showed significantly higher color stability than TP chains,and products by OR and GH had better color stability than the products by AO. Conclusion: The present studyshowed that TS chains were superior to TP chains in force decay and color stability in all the brands studied.KEYWORDSColor; Elastomeric; Force decay; Thermoplastic; Thermoset.

In-Plane Strengthening of Unreinforced Masonry Walls by Glass Fiber-Reinforced Polyurea

Strengthening techniques have been employed in Korea to unreinforced masonry walls (UMWs) for several years to protect them from damage caused by the intermittent occurrence of earthquakes. Polyurea, which has a high tensile strength and elongation rate, can be utilized as a strengthening material to enhance the in-plane strength and ductility of UMWs. Glass fiber-reinforced polyurea (GFRPU) is a composite elastomer manufactured by progressively adding milled glass fiber to polyurea. The purpose of this study is to investigate the enhancement of the in-plane strength and ductility of UMWs using GFRPU, depending on the shape of the GFRPU coating on the wall. Four masonry wall specimens are tested with test variables of the number of strengthening sides and coating shapes. It is illustrated that the GFRPU reinforcement of masonry wall leads to enhanced load-carrying capacity, ductility, and energy absorption. An empirical formula to represent the degree of strengthening effected by GFRPU is proposed in this study. Doi: 10.28991/cej-2021-03091782 Full Text: PDF

Effect of Cu addition on the microstructure, mechanical properties and degradation rate of Mg-2Gd alloy

The demand for magnesium (Mg) alloy with high elongation, certain strength and good degradation rate used in oil and gas exploitation filed is increasing. Based on Mg-2Gd alloy, effect of copper (Cu) addition (0.25, 0.5 and 0.75 wt.%) on microstructure, mechanical properties and degradation rate were investigated. It showed that more Mg 2 Cu second phases were precipitated and the grain size was refined with increasing Cu content, accompanied with texture changing from < 11 2 ¯ 1 > //ED to < 01 1 ¯ 0 > //ED. As a result, hardness, tensile strength, compressive strength and degradation rate were enhanced while the strain hardening rate and elongation decreased. Nevertheless, the elongation was still up to at least 20%. Overall, the comprehensive mechanical properties and degradation rate of Mg-2Gd alloy can be effectively coordinated by Cu addition.

Electroconductive Graphene-Combined Polycaprolactone Electrospun Films for Biological Applications

This study produces electroconductive polycaprolactone (PCL)-based film with different amounts of graphene (G) through electrospinning, and the characteristics of the produced G/PCL composites are investigated. The G/PCL results are analyzed by comparing them with those obtained using pure PCL electrospun film as a control. The morphology of electrospun material is analyzed through scanning electron microscopy and transmission electron microscopy. Mechanical and electrical properties are also evaluated. Composites containing 1% graphene have the highest elongation rate, and 5% samples have the highest strength and elasticity. Graphene contents > 25% show electro-conductivity, which level improves with increase of graphene content. Biological characteristics of G/PCL composites are assessed through behavioral analysis of neural cell attachment and proliferation. Cell experiments reveal that compositions < 50% show slightly reduced cell viability. Moreover, graphene combinations facilitated cell proliferation compared to pure PCL. These results confirm that a 25 % G/PCL composition is best for application to systems that introduce external stimuli such as electric fields and electrodes to lead to synergistic efficiency of tissue regeneration.

Electrical Characterization of a Double-Layered Conductive Pattern with Different Crack Configurations for Durable E-Textiles.

For the conductive patterns of electronic textiles (e-textiles), it is still challenging to maintain low electrical resistance, even under large or cyclic tensile deformation. This study investigated a double-layered pattern with different crack configurations as a possible solution. Patterns with single crack growth exhibit a low initial resistance and resistance change rate. In contrast, patterns with multiple crack growth maintain their conductivity under deformation, where electrical failure occurs in those with single crack growth. We considered that a double-layered structure could combine the electrical characteristics of patterns with single and multiple crack growths. In this study, each layer was theoretically designed to control the crack configuration. Then, meandering copper patterns, silver ink patterns, and their double layers were fabricated on textiles as patterns with single and multiple crack growths and double-layered patterns, respectively. Their resistance changes under the single (large) and cyclic tensile deformations were characterized. The results confirmed that the double-layered patterns maintained the lowest resistance at the high elongation rate and cycle. The resistance change rates of the meandering copper and silver ink patterns were constant, and changed monotonically against the elongation rate/cycle, respectively. In contrast, the change rate of the double-layered patterns varied considerably when electrical failure occurred in the copper layer. The change rate after the failure was much higher than that before the failure, and on the same order as that of the silver ink patterns.

Pathologic Shear and Elongation Rates Do Not Cause Cleavage of Von Willebrand Factor by ADAMTS13 in a Purified System.

Pathological flows in patients with severe aortic stenosis are associated with acquired von Willebrand syndrome. This syndrome is characterized by excessive cleavage of von Willebrand factor by its main protease, A Disintegrin and Metalloproteinase with a Thrombospondin Type 1 Motif, Member 13 (ADAMTS13) leading to decreased VWF function and mucocutaneous bleeding. Aortic valve replacement and correction of the flow behavior to physiological levels reverses the syndrome, supporting the association between pathological flow and acquired von Willebrand syndrome. We investigated the effects of shear and elongational rates on von Willebrand factor cleavage in the presence of ADAMTS13. We identified acquired von Willebrand syndrome in five patients with severe aortic stenosis. Doppler echography values from these patients were used to develop three computational fluid dynamic (CFD) aortic valve models (normal, mild and severe stenosis). Shear, elongational rates and exposure times identified in the CFD simulations were used as parameters for the design of microfluidic devices to test the effects of pathologic shear and elongational rates on the structure and function of von Willebrand factor. The shear rates (0-10,000s-1), elongational rates (0-1000 s-1) and exposure times (1-180 ms) tested in our microfluidic designs mimicked the flow features identified in patients with aortic stenosis. The shear and elongational rates tested in vitro did not lead to excessive cleavage or decreased function of von Willebrand factor in the presence of the protease. High shear and elongational rates in the presence of ADAMTS13 are not sufficient for excessive cleavage of von Willebrand Factor.

Biomechanical Comparison of Graft Preparation Techniques for All-Inside Anterior Cruciate Ligament Reconstruction

Background:All-inside anterior cruciate ligament reconstruction (ACLR) is an emerging technique used to treat ACL injuries. The all-inside technique uses a 4-stranded graft made from a single tendon that is looped on itself. The 4 strands of the graft must be secured to each other to become a closed-loop structure. Various suture configurations exist to secure the graft to adjustable loop devices, and there is a lack of data to support one technique over another. In addition to the primary sutures used to fasten the graft together, accessory sutures can be tied over the button as secondary fixation.Purpose:To evaluate biomechanical properties of 4-stranded grafts prepared in 5 different configurations.Study Design:Controlled laboratory study.Methods:Porcine flexor tendons (N = 25) were prepared in 5 different configurations (n = 5 tendons per group): simple-interrupted sutures (unsecured fixation), side-to-side fixation with and without secondary fixation, and end-to-end fixation with and without secondary fixation. The grafts were put through the same mechanical testing protocol (cyclic loading, pull to failure) to measure average load at graft failure, average displacement at failure, average stiffness, and average elongation rate. Differences between graft preparation techniques were investigated using 1-way analyses of variance (ANOVAs) with post hoc t tests (P < .05).Results:Significant 1-way ANOVAs for each biomechanical property were found. Unsecured fixation was the weakest graft preparation with the lowest stiffness (167 ± 12 N/mm), lowest ultimate failure load (637 ± 99 N), and highest elongation rate (0.0033 ± 0.0007 mm/s). End-to-end fixation without secondary fixation showed the highest ultimate failure load (846 ± 26 N), highest stiffness (212 ± 10 N/mm), and lowest rate of elongation (0.0025 ± 0.0001 mm/s). End-to-end fixation, both with and without secondary fixation, as well as side-to-side fixation with secondary fixation showed significantly higher ultimate failure loads than grafts with unsecured fixation. End-to-end fixation performed better than side-to-side fixation; however, for most variables, the difference was not statistically significant. Secondary fixation did not provide significant improvement.Conclusion:The all-inside ACL graft with simple-interrupted sutures is biomechanically inferior to a graft that has its free ends secured to the adjustable tibial loop. Adding secondary fixation to the tibial button does not significantly change the biomechanical properties. Further clinical studies are required to determine whether these findings translate into differences in clinical outcome.Clinical Relevance:All-inside ACLR is gaining popularity in hamstring ACL reconstructive techniques. These results provide surgeons with guidance on the best graft preparation method when using a single quadrupled hamstring tendon graft.

Electrospinning of polymer solutions: An analysis of instability in a thinning jet with solvent evaporation

The present study examines the stability of a thinning straight jet in electrospinning process. The linear stability analysis is carried out to obtain the growth/decay rate of axisymmetric disturbance imposed on the thinning jet. The analysis captures the role of solvent evaporation in the stability behavior of the linear path of the electrospinning jet. In contrast to many prior stability analyses which consider the jet as a cylindrical filament with uniform radius, the present study analyzes the stability of a jet which exhibits thinning under realistic electrospinning conditions. Two different polymeric solutions are considered: the poly-isobutene (PIB) Boger fluid with low electrical conductivity and the highly conductive poly-ethylene oxide (PEO) solution in ethanol/water. At low extensional deformation, the rheology of the unentangled PIB-based Boger fluid is described by the Oldroyd-B model. The PEO solution, on the other hand, experiences a very high elongation rate due to the development of strong axial electric stress. The nonlinear rheology of the entangled PEO solution is appropriately described by the eXtended Pom–Pom (XPP) model, a variant of the classical tube model. The analysis reveals that the instability in low conductivity fluid is driven by the capillary forces, whereas the high conductivity fluid exhibits oscillatory conducting mode of instability driven by the coupled effect of axial electric field and surface charges. For both the reference fluids, the increase in solvent evaporation tends to decrease the disturbance growth rate to the extent that the axisymmetric instability is completely suppressed for a strong enough evaporation. The stabilizing role of solvent evaporation is attributed to the enhancement in fluid viscosity and elasticity due to increased polymer concentration upon evaporation. Thus, by suppressing the onset of axisymmetric instability during the straight jet path, solvent evaporation potentially helps produce smooth fibers without bead formation.

The morphogenesis of marandu palisadegrass at fixed or variable heights in different seasons of the year

Height variations in a sward over the year may be efficient for increasing plant growth, compared with maintenance of the sward at a constant height. Thus, this experiment was conducted from February 2013 to May 2014 to characterise the development of Urochloa brizantha syn. Brachiaria brizantha cv. Marandu (marandu palisadegrass), managed under three defoliation strategies: constant height (30 cm during the entire experimental period), increasing height (15 cm in the winter, 30 cm in the spring, and 45 cm in the summer), and decreasing height (45 cm in the winter, 30 cm in the spring, and 15 cm in the summer). The experimental design was completely randomised, in a split-plot arrangement, with four replicates. Phyllochron was higher in the winter, but leaf and stem elongation rates and the number of live leaves per tiller were lower compared with the spring and summer. In the summer, the swards under increasing height displayed a higher phyllochron than those under decreasing and constant height. When comparing seasons, the highest leaf senescence rate occurred in spring. In the winter, the sward with increasing height had shorter leaves and stems, in contrast to the summer. The sward under decreasing height showed a high stem elongation rate in the spring. Marandu palisadegrass has great flexibility in terms of defoliation management and a typical seasonal development pattern. Modifying the sward height results in a gradual change in the development of marandu palisadegrass and generates residual effects on the subsequent season.

Effects of Blade Tip Profile on In-Plane Tensile Properties of Wedge-Notched Polypropylene Sheet

In this work, the tensile characteristics of a 0.2-mm-thick polypropylene (PP) sheet subjected to indentation with virgin and blunt knives (apex angle, α=42◦; tip thickness, w=6 and 20 μm, respectively), were experimentally investigated. To determine the effect of mechanical condition, such as the notched depth and the profile of the root surface, on the breaking behavior of the half-cut PP specimen, the tensile testing of the half-cut specimen was carried out by varying the indentation depth and tensile velocity. By the experiments, the breakage behavior of the scored (half-cut) zone was determined by varying the indentation depth, tip thickness of the blade, and elongation rate. A kind of crazing or cracking by the blunt knife decreased the tensile resistance and burr elongation for an indentation depth larger than 0.9, whereas the work hardening by the blunt knife increased these properties for an indentation depth less than 0.8. When a blunt knife was used at a high elongation rate larger than 0.01 s-1, the half-cut zone of the PP sheet exhibited brittle fracture, i.e., the tensile resistance and burr elongation decreased.