Room Temperature Impact Strength Research Articles

Synthesis of Hyperbranched Flame Retardants with Varied Branched Chains' Rigidity and Performance of Modified Epoxy Resins.

To overcome the high flammability and brittleness of epoxy resins without sacrificing their glass transition temperature (Tg) and mechanical properties, three epoxy-terminated hyperbranched flame retardants (EHBFRs) with a rigid central core and different branches, named EHBFR-HB, EHBFR-HCM, and EHBFR-HBM, were synthesized. After chemical structure characterization, the synthesized EHBFRs were introduced into the diglycidyl ether of bisphenol A (DGEBA) and cured with 4, 4-diaminodiphenylmethane (DDM). The compatibility, thermal stability, mechanical properties, and flame retardancy of the resultant resins were evaluated. Results showed that all three EHBFRs could significantly improve the fire safety of cured resins, and 30 wt. % of EHBFRs (less than 1.0 wt. % phosphorus content) endowed cured DGEBA with a UL-94 V-0 rating. In addition, the increased rigidity of branches in EHBFRs could increase the flexural strength and modulus of cured resins, and the branches with appropriate rigidity were also beneficial for improving their room temperature impact strength and Tg.

Influence of the process parameters of an intermeshing co-rotating twin screw extruder on the morphology and notched Izod impact strength of PBT/ABS/MGE blends

In this research, it was studied the effects of the processing parameters applied to a twin screw extruder on the morphology and impact strength of poly(butylene terephthalate)/acrylonitrile-butadiene-styrene blends with and without a reactive compatibilizer. It was found that the increase of the feed rate highly decreased the ductile brittle transition temperature (DBTT) and slightly increased the room temperature impact strength (RTIS) of the compatibilized blends. Besides the influence of the feed rate, it was also found that the compatibilized blends could reach high RTIS and low DBTT values by an appropriate combination of the compatibilizer feeding position in the extruder, the screw rotation speed and the width of the kneading discs of the screw. The DBTT was found to be at least partially controlled by the spatial distribution of the rubbery particles, which was quantified by finite body tessellation, a method applied for the first time in polymer blends. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers

Properties of compatibilized nylon 6/ABS blends: Part I. Effect of ABS type

Blends of nylon 6 with four acrylonitrile–butadiene–styrene (ABS) materials were investigated over a range of compositions using an imidized acrylic (IA) polymer as the compatibilizing agent. The IA material is miscible with the SAN matrix and is able to react with the amine end groups of nylon 6 during melt processing. The effects of ABS type and blend composition on the morphological, rheological and mechanical behavior of these blends were explored at a fixed (5wt.%) compatibilizer content. In general, incorporation of the IA polymer can lead to super tough blends using a broad range of ABS materials. Of the ABS materials used, those with a monodisperse population of butadiene rubber particles and low melt viscosity were found to generate blends with superior low temperature toughness compared to those with broad particle size distributions and higher viscosity. In several compatibilized blends, increasing the ratio of nylon 6 to ABS improved the modulus and yield strength and did not significantly affect the room temperature impact strength up to a certain level; however, the ductile-to-brittle transition temperatures of these blends were quite sensitive to the amount of rubber in the blend, and increased steadily with increasing nylon 6/ABS ratio. The effect of compatibilizer content on blend properties was determined at a fixed ratio of nylon 6 to ABS. Super tough materials can be generated using very small (0.5wt.%) amounts of the imidized acrylic polymer. Further increases in compatibilizer content did not significantly affect the room temperature impact strength, but did improve the low temperature toughness. When processing characteristics are considered, there is no justification to use more than about 2wt.% of this compatibilizer.

Effect of adding an imidized acrylic polymer to super tough nylon 6 on stiffness and toughness

The mechanical properties and phase morphology of ternary blends of nylon 6 with rubber, e.g., maleated ethylene-propylene random copolymer (EPR-g-MA) or maleated styrene-(ethylene-co-butylene)-styrene (SEBS-g-MA), and a rigid but brittle imidized acrylic polymer (IA) are explored. The objective was to investigate blends which have independently dispersed rubber and rigid polymer particles in a nylon 6 matrix. The amount of rubber was fixed at 20%, while the IA to nylon 6 ratio was varied. Addition of imidized acrylic polymer particles to nylon 6 toughened by EPR-g-MA particles leads to increased stiffness and room-temperature impact strength and does not change the ductile-to-brittle transition temperatures up to a critical level. Similar improvements in stiffness and room temperature impact strength were found for nylon 6 toughened by SEBS-type rubber; however, the low temperature impact properties were not as good.

Effect of compatibilization and ABS type on properties of PBT/ABS blends

Toughened blends of poly(butylene terephthalate) (PBT) with appropriate ABS materials can be prepared without a compatibilizer within limited melt processing situations. As illustrated by transmission electron microscopy, coarsening of uncompatibilized blends occurs under certain molding conditions resulting in a deleterious effect on blend properties. Methyl methacrylate, glycidyl methacrylate (GMA), ethyl acrylate (MGE) terpolymers were shown to be effective reactive compatibilizers for PBT/ABS blends that broaden the processing window and provide improved low temperature impact properties, ABS dispersion, and morphological stability. A twin screw extruder is more effective than the single screw extruder used here for processing these reactive blends. Several ABS types with different rubber contents were examined; generally, materials with very high rubber contents were found to be more beneficial for toughening PBT. Among these high rubber content materials, the ABS material having the lowest melt viscosity was found to be superior for optimizing morphology and impact properties. At leat 30% of this material, containing a minimum of 36% rubber, is required for producing toughened blends. Moderate amounts of GMA functionality in the compatibilizer (>5%) and small amounts of compatibilizer in the blend (<5%) significantly improve low temperature impact properties and ABS dispersion. Higher amounts of GMA in the blend increase the room temperature impact strength with little effect on the ductile–brittle transition temperature and increase blend viscosity.

Effect of crosslinking reactions and order of mixing on properties of compatibilized PBT/ABS blends

The low-temperature notched Izod impact strength of poly(butylene terephthalate), PBT, blends with acrylonitrile–butadiene–styrene terpolymers, ABS, can be improved by incorporating methyl methacrylate, glycidyl methacrylate, ethyl acrylate terpolymers, MGE, as a reactive compatibilizer. However, fracture properties depend on the order of mixing of the blend components. When all components of compatibilized blends are melt mixed together in a single-pass extrusion, the low-temperature toughness is improved; however, the room-temperature impact strength is reduced relative to uncompatibilized blends. Using a two-pass extrusion method where PBT and MGE are melt mixed together in a first extrusion prior to incorporating ABS in a second extrusion, the room-temperature impact strength is superior to that of blends prepared by the single-pass method. When a two-pass method is used where ABS and MGE are combined prior to extrusion with PBT, the impact properties at all temperatures are inferior to those of uncompatibilized blends. Evidence is presented which suggests that residual acids present in emulsion-made ABS material may cause a crosslinking reaction involving the epoxide functionality of MGE terpolymers resulting in a deleterious effect on the ABS mechanical properties and its blends with PBT. By changing the order of mixing, the sequence of chemical reactions which occur can be controlled to optimize blend properties.

Phase transformations in ferrite phase of a duplex stainless steel aged at 500°C

Due to their high strength, high corrosion resistance, and good properties of castings, duplex stainless steels are widely used in the recirculation system of nuclear power plants. Although the presence of ferrite phase increases the strength and the resistance to SCC, the ferrite phase also brings about thermal aging embrittlement known as 475°C embrittlement[1,2]. The room temperature impact strength can decrease by 80% after aging for 8 years at a temperature as low as 300°C[3]. Much research[4- 10] has been performed on the low temperature embrittlement of duplex stainless steels. It is generally acknowledged that the spinodal decomposition in ferrite phase and precipitation of some other carbides or nickel silicide(G phase)[4] are responsible for the degradation in mechanical properties of duplex stainless steels at low temperatures. The extent of the degradation was found to be strongly dependent on the composition in ferrite[7,8], which is closely related to the change of microstructure. Thus, the exact evolution of phase transformation in ferrite has also drawn a large audience. In this study, using electron microscopy, we investigated the phase evolution of ferrite phase in duplex stainless steel, aged at 500°C up to 10,000 hours.

Some studies on glass fiber‐reinforced polypropylene. Part II: Mechanical properties and their dependence on fiber length, interfacial adhesion, and fiber dispersion

AbstractTwo commercial grades of glass fiber‐reinforced polypropylene granules, one containing short fibers of average length around 0.5 mm with a coupling agent and the other containing relatively much longer fibers mostly around 9 mm, but no coupling agent, were injection‐molded into dumbbells and tested in tension between −43 and 90°C. There is considerable fiber attrition during injection molding; the fiber lengths are reduced to average values of 0.4 to 0.8 mm for thses two samples. Also during injection molding of the test sample, partial molecular alignment of the matrix (polypropylene) occurs which supplements the reinforcement of the matrix due to the aligned glass fibers (30 percent by weight) present in the composite sample. The stiffness and strength of these samples do not reflect the effects of fiber lengths since most of the fibers are of very small length in the molded specimen and also since the sample with longer fibers has a non‐uniform distribution of fibers. While the interfacial shear strength does not appear to play a significant role in determining stiffness, it turns out to be extremely important in controlling strength, particularly at the higher test temperatures. The room temperature impact strength is high for the sample containing relatively longer fibers of average length around 0.8 mm in which fiber dispersion is non‐uniform and fiber agglomerates are present. Acoustic emission data shows that debonding and fiber pull‐out are the main contributors to sample toughness; this observation is supported by scanning electron micrographs of the fracture surfaces.

Effect of notch-root radius and-high austenitizing temperatures on impact properties of 300M steel

AbstractThe effect of notch-root radius, austenitizing temperature, and austenitizing time on the room-temperature impact strength and the ductile-brittle transition characteristics of tempered 300M steel have been investigated. For high-strength, medium-carbon, low-alloy steels high-temperature austenitizing treatments are known to give contradictory results with regard to the toughness characteristics. The plane-strain fracture toughness and the prefatigue-cracked impact strength are increased whereas the standard impact strength is decreased. The present investigation has shown that the impact strength is increased with increasing austenitizing temperature if the notch-root radius is less than 0·13 mm but for blunter notches it is decreased when the treatment temperature is above 1000°C. For high-temperature austenitizing treatments the impact strength, for all notch-root radii, is increased with austenitizing time but/or the low austenitizing treatments the impact strength is independent of time. The ...

THE EFFECT OF DEFORMATION ON TENSILE AND IMPACT PROPERTIES OF HOT PM-FORMED NICKEL-MOLYBDENUM STEELS

Hardenability, tensile, and impact properties have been determined for two nickel-molybdenum powder-formed steels. The compositions of the two steels were Fe-1·8% Ni−0·5% Mo and Fe −0·5% Ni −0·6% Mo; carbon contents studied for both materials were 0·2, 0·3, and 0·4%. Preforms (50 × 50 × 127 mm) were pressed and then sintered for 1 h in a dissociated ammonia atmosphere at 1120°C, to provide a density of 6·5 g/cm3. Preforms were hot formed to full density by upsetting (plane strain) at 980°C or by re-pressing (uniaxial strain) at 1040°C.Standard 25 mm-dia. × 100 mm-long Jominy end-quenched tests were made to determine hardenability. Room-temperature tensile properties were determined using 6·4 mm-dia. specimens with a 25 mm gauge-length. Standard Charpy V-notch specimens were used to determine the impact properties at −40, 0, 22, and 100°C. Triplicate tests were made in the as formed as well as the quenched-and-tempered conditions.The additional flow that was realized by upsetting provided higher tensile and impact strengths than re-pressing. Tensile ductility was the same for both processing conditions. Tensile yield strength (heat-treated to ∼26 HV) increased with increasing carbon content for the slack quenched material and levelled off for fully martensitic structures. Room-temperature impact strength also increased with increasing carbon content owing to a decrease in the amount of ferrite in the slack quenched structure. Increasing carbon content caused a decrease in impact strength once fully martensitic structures were achieved.Impact strength at −40°C ranged from ∼20 to 40 J. Room-temperature impact strength ranged from ∼20 to 50 J. These properties were obtained for materials heat-treated to a UTS level of ∼850 N/mm2. At the lower carbon contents the hardenability curve was found to fall within the AISI ‘H’ band for 4620 wrought steel. At the higher carbon level (0.4% C) the Jominy curves were close to the lower limit of the ‘H’ band for the 4640 wrought steels.

Intermetallic compounds and their mechanical behavior

Available information on the mechanical behavior of intermetallic compounds and its relation to relevant metallurgical phenomena and test parameters is reviewed. Brittleness at low homologous temperatures is indicated to be the most serious shortcoming of these compounds. But the room-temperature impact strength of intermetallic compounds is high compared to the refractory interstitial compounds. Furthermore, there are indications that the ductility of intermetallic compounds can be improved.