Fatigue properties of vibration‐welded postindustrial waste nylon with glass fibers at room and elevated temperatures

The effect of temperature on the tensile and fatigue strength of vibration‐welded and unwelded postindustrial waste nylon 6 reinforced with 30 wt% glass fiber (PIWGF) was experimentally examined, and the results were compared to those obtained from a 30 wt% glass fiber reinforced prime nylon 6 compound (PAGF) from a previous study. Fatigue tests were performed under sinusoidal constant amplitude tension‐tension load at a stress ratio of R = 0.1 and within the frequency range of 2–10 Hz at temperatures from 24 to 120°C. Stress levels from just under the tensile strength down to the run‐out point at 5 million cycles were used. It was found that increasing temperature led to a significant decrease in both tensile strength and fatigue life. For PIWGF, there was ～20% strength reduction under both static tensile and cyclic loading as compared to PAGF. For both welded and unwelded PIWGF, the endurance ratio; i.e., the ratio of fatigue strength to static tensile strength, was ～45% regardless of the temperature. The fatigue notch factor (K_f) was between 1.4 and 1.8 for all test temperatures examined. POLYM. ENG. SCI., 55:799–806, 2015. © 2014 Society of Plastics Engineers     

Effects of melt temperature and hold pressure on the tensile and fatigue properties of an injection molded talc‐filled polypropylene

This article examines the effects of melt temperature and hold pressure on the static tensile and fatigue behavior of an injection‐molded 40 wt% talc‐filled polypropylene. Injection molding caused anisotropy in the material. Both yield strength and fatigue strength were higher in the flow direction. The presence of weld line caused a large reduction in yield strength and fatigue strength. For specimens in the flow direction, both yield strength and fatigue strength increased with increasing hold pressure, but they were relatively insensitive to melt temperature. For specimens normal to the flow direction, both yield strength and fatigue strength increased with increasing hold pressure and decreased with increasing melt temperature. For specimens containing a weld line, the yield strength and fatigue strength increased with increasing hold pressure as well as increasing melt temperature. The observed differences in properties are explained in terms of the skin‐core morphology, which was influenced by both melt temperature and hold pressure. POLYM. ENG. SCI., 45:755–763, 2005. © 2005 Society of Plastics Engineers     

Weld lines in nylon 6 melt‐blended nanocomposites

The effects of weld lines in injection moldings of nylon 6 and nylon 6 nanocomposite samples were investigated by comparing single‐end‐gated and double‐end‐gated tensile samples. The single‐gated samples have no weld line, whereas the double‐end‐gated configuration produces a weld line at the center of the gauge length. Nylon 6 shows little variation in tensile properties for samples with or without weld lines, remaining ductile and tough, even with weld lines present. However, nylon 6 nanocomposites containing organically modified montmorillonite (organoclay), produced by a melt blending technique, exhibits rigid and brittle behavior for both single (no weld line) and double‐end‐gated (with weld line) samples. The organoclay increases the tensile strength but reduces the strain‐to‐failure significantly in both cases. A modified L₁₆ orthogonal array based on the Taguchi approach with three levels was designed to run injection‐molding experiments to allow production of a modest number of samples to identify the most important process factors. The results were analyzed using the statistical tools signal‐to‐noise (S/N) ratio and analysis of variance (ANOVA), in particular showing that the principal process factors for the double‐end‐gated nylon 6 nanocomposite samples are mold and melt temperatures. POLYM. ENG. SCI., 45:1606–1614, 2005. © 2005 Society of Plastics Engineers     

Fatigue performance of an injection‐molded short E‐glass fiber‐reinforced polyamide 6,6. I. Effects of orientation,holes, and weld line

This article presents the experimental results of stress‐controlled fatigue tests of an injection‐molded 33 wt% short E‐glass fiber‐reinforced polyamide 6,6. The effects of specimen orientation with respect to the flow direction, hole stress concentration, and weld line on the fatigue life have been considered. In addition, the effect of cyclic frequency has been examined. In addition to the modulus and tensile strength, the fatigue strength of the material was significantly higher in the flow direction than normal to the flow direction, indicating inherent anisotropy of the material caused by flow‐induced orientation of fibers. The presence of weld line reduced the modulus, tensile strength, failure strain, and fatigue strength. The fatigue strength of specimens with a hole was lower than that of un‐notched specimens, but was insensitive to the hole diameter. At cyclic frequencies ≤ 2 Hz, failure was due to fatigue, and fatigue life increased with frequency. However, at cyclic frequencies > 2 Hz, the failure mode was a mixture of fatigue and thermal failures, and fatigue life decreased with increasing frequency. POLYM. COMPOS., 27:230–237, 2006. © 2006 Society of Plastics Engineers.     

Fatigue performance of an injection molded talc‐filled polypropylene

This paper reports the fatigue behavior of an injection molded 40wt% talc‐filled polypropylene. The effects of specimen orientation relative to the flow direction, weld line, hole stress concentration and test frequency on the fatigue performance of this material have been considered. The fatigue strength in the flow direction was higher than that normal to the flow direction. However the orientation effect decreased at lower fatigue stress level. The presence of weld line reduced the fatigue strength. On the other hand, the fatigue strength showed very little sensitivity to the presence of hole stress concentration. The failure mode in fatigue was influenced by the test frequency. When the test frequency was less than or equal to 2 Hz, the failure mode of the talc‐filled polypropylene was due to fatigue and the fatigue life increased with frequency. However, when the test frequency was greater than or equal to 5 Hz, the failure of the talc‐filled polypropylene was due to thermal softening and the fatigue life did not appear to be influenced much by the frequency. POLYM. ENG. SCI., 45:510–516, 2005. © 2005 Society of Plastics Engineers     

Fatigue performance of injection‐molded short e‐glass fiber reinforced polyamide‐6,6. II. Effects of melt temperature and hold pressure

Tensile and fatigue properties of an injection molded short E‐glass fiber reinforced polyamide‐6,6 have been studied as a function of two key injection molding parameters, namely melt temperature and hold pressure. It was observed that tensile and fatigue strengths of specimens normal to the flow direction were lower than that in the flow direction, indicating inherent anisotropy caused by injection molding. Tensile and fatigue strengths of specimens with weld line were significantly lower than that without weld lines. For specimens in the flow direction, normal to the flow direction and with weld line, tensile strength and fatigue strength increased with increasing melt temperature as well as increasing hold pressure. The effect of specimen orientation on the tensile and fatigue strengths is explained in terms of the difference in fiber orientation and skin‐core morphology of the specimens. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers.     

Mechanical Behavior and Applications of Plasma Arc Welded Ceramics

Zirconium diboride and zirconium carbide‐based ceramics were joined by plasma arc welding to demonstrate the versatility of this technique. A parent material composition consisting of ZrB₂ with 20 vol% ZrC was hot pressed to near full density, sectioned to produce specimens for welding, and welded together to produce billets for mechanical property studies. The four‐point flexure strength of the parent material was ~660 MPa, while the strength of the welded specimens ranged from ~140 to ~250 MPa. Microstructural analysis revealed that decreased strength in the welded specimens was caused by volume flaws, microcracking of large ZrB₂ grains (up to 1 mm in length), and residual tensile stresses that developed at the surface of weld pools during cooling. The versatility of plasma arc welding was demonstrated by joining of ZrC‐based ceramics and fabricating three ZrB₂–ZrC components for potential applications, including a high‐temperature electrical contact, an ultra‐high‐temperature thermocouple, and a wedge that was a notional wing leading edge. These three applications demonstrated the ability to join ceramics to a refractory metal, fabricate a chemically inert high‐temperature thermocouple, and produce complex shapes for aerospace applications.     

Preparation of conducting nylon‐6 electrospun fiber webs by the in situ polymerization of polyaniline

For the preparation of conducting polyaniline (PANI)/nylon composites with high electrical conductivity as well as superior mechanical properties such as flexibility and lightness, PANI/nylon‐6 composite nanofiber webs were prepared via the electrospinning process with a nylon‐6/formic acid polymer solution, and then PANI on the surface of the nylon‐6 electrospun nanofiber webs was chemically polymerized. The electrical conductivity measurements showed that the conductivity of the PANI/nylon‐6 composite electrospun fiber webs was superior to that of PANI/nylon‐6 plain‐weave fabrics because of the high surface‐area/volume ratios. On the other hand, the volume conductivities of the PANI/nylon‐6 composite electrospun fiber webs increased from 0.5 to 1.5 S/cm as the diffusion time increased from 10 min to 4 h because of the even distribution of PANI in the electrospun fiber webs. However, the surface conductivities of the PANI/nylon‐6 composite electrospun fiber webs somewhat decreased from 0.22 to 0.14 S/cm as the diffusion time increased because of PANI contaminated with aniline monomers, aniline oligomers, and some alkyl chains, which served as electrical resistants. These results were confirmed with Fourier transform infrared, electron spectroscopy for chemical analysis, and morphology analysis. It was concluded that the diffusion time for the in situ polymerization of PANI in electrospun fiber webs was optimized at approximately 3 h. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 983–991, 2005     

Identification of caprolactam oligomers and related compounds in aqueous extracts of nylon‐6

Cyclic oligomers of caprolactam were isolated from a multilayered polyolefin plastic film containing a nylon‐6 layer and subsequently characterized. Nylon‐6 was extracted with aqueous solutions and the levels of the oligomers were measured in the resulting extracts. Oligomers up to n = 5 were present at high and comparable levels in all the nylon‐6 extracts. The levels of the oligomers dropped off rapidly with increased compound size after n = 5, with the heptamer being barely observable in the extract chromatograms. The effect of extracting solution pH on the compound's concentration in the extract was small, except for the monomer, whose accumulation was significantly decreased at low pH. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1262–1274, 2005     

Influence of thickness and processing history on fatigue fracture of nylon 66. Part I: Crack propagation measurements

The influence of sample thickness on fatigue crack propagation rates in injection molded nylon 66 was determined by preparing 12.7 mm thick plaques along with more conventional 3.0 mm thick samples. Initial results suggested a large effect of thickness as the crack propagation rates were accelerated in the thicker samples and the stress dependence was also increased. Since the calculated thickness for a plane stress to plane strain transition in nylon 66 is 9.0 mm, it was thought that these results were related to the stress state at the crack tip. However, a more thorough study of the thicker plaques has now demonstrated that neither the magnitude nor the stress dependence of the fatigue crack growth rates is necessarily changed under plane strain conditions as similar results can be obtained for thick and thin plaques. It is suggested that the earlier results were confounded by a previously unrecognized processing history effect which does accelerate fatigue fracture. The latter effect is shown by thermal analysis and optical microscopy to be related to a rearrangement of the polymer network during melt processing.     

Influence of Weldling Parameters on Weldline Density and Its Relation to Crack Formation in Welded Scots Pine Joints

Exterior use of welded wood laminates without further treatment is not recommended. Frictional welded joints have poor resistance to moisture variation, especially to drying. Therefore, application of welded woods is limited to interior use without exposure to highly variable air humidity. Influences of some welding and wood parameters such as welding pressure, welding time and heartwood/sapwood on weldline density of Scots pine (Pinus sylvestris) joints were investigated. Interdependence between density and water resistance of weldline (in terms of crack time) was also studied by comparing the results of this investigation with those of the earlier studies. Specimens composed of two wood pieces, each measuring 20 mm × 20 mm × 200 mm, were welded together to form a specimen measuring 40 mm × 20 mm × 200 mm by a vibration movement of one wood surface against another at a frequency of 150 Hz. An X-ray Computerized Tomography scanner was used to measure weldline density. Weldlines of sapwood produced by 1.3 MPa welding pressure and 1.5 s welding time showed the highest density. No correlation between weldline density and crack time was evident.     

Tensile properties of denture base resin reinforced with various esthetic fibers

This study was conducted to determine the reinforcement effect of five types of esthetic fibers on the tensile properties of a conventional denture base resin. E‐glass, polyester, rayon, nylon 6, and nylon 6/6 fibers were cut into 2, 4, and 6 mm lengths and added into resin randomly at a concentration of 3% by weight. For each formulation, five tensile specimens, as well as control specimens without fibers, were prepared in a dumbbell shape using a stainless steel mold, constructed according to ASTM Standard D638M‐91a. Tensile properties were evaluated by using a universal testing machine. Surfaces of the tensile sections were also observed under the scanning electron microscope (SEM). Tensile strength of the specimens reinforced with fibers in varying lengths was found to be lower than that of the unreinforced control group. Among the trial groups, the specimens reinforced with 6 mm long polyester fibers showed the highest tensile strength. All the SEM fractographs indicated both weak adhesion and pull out of fibers from the matrix. None of the incorporated esthetic fibers appeared to improve tensile strength of the resin. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The preparation and properties of compatibilized nylon 6/ABS blends using functionalized polybutadiene. Part I: Impact properties

The impact behaviors of nanoclay filled nylon 6 (nano‐nylon 6) or nylon 6 blended with poly(acrylonitrile‐butadiene‐styrene) terpolymers (ABS) were investigated here using polybutadiene grafted maleic anhydride (PB‐g‐MA) as a compatibilizer to enhance interphase interaction. It is found that impact strength increases slightly for nano‐nylon 6/ABS blend system with the addition of compatibilizer at various ABS compositions, but increases to a certain degree for nylon 6/ABS case. Similar effects are also found with decreasing test temperature, especially at a blend composition of 80/20. These discrepancies are attributed to a different degree of available reaction sites from amine group on nano‐nylon 6 and nylon 6 as well as the rigidity of clay in deteriorating toughness. As for thermal properties, the heat distortion temperature shows marginally decrease in the nano‐nylon 6/ABS blend. Through morphology observations, the etched ABS particle sizes tend to decrease with the additions of compatibilizer for both blends, but are larger with higher contents of ABS concentrations. Those observations account for impact behaviors of the investigated blends. POLYM. ENG. SCI., 45:1461–1470, 2005. © 2005 Society of Plastics Engineers     

The vibration welding of polycarbonate/acrylonitrile‐butadiene‐styrene blends to themselves and to other resins and blends

The weldabilities of two commercial blends of polycarbonate (PC) and acrylonitrile‐butadiene‐styrene (ABS) to themselves and to several other resins and blends are assessed through 120 Hz vibration welds of 6.35‐ and 3.2‐mm‐thick specimens. While the thicker specimens of both blends have relative weld strengths of 83%, the thinner specimens in one of the grades have a lower relative weld strength of 73%. Welds of thicker specimens of both grades to PC have relative strengths of 85%. Again, welds of thinner specimens of one of the grades to PC have a lower relative strengths of 68%. Welds of the thinner specimens of this grade with ABS have relative strengths of 85%. Welds of this material with poly(butylene terephthalate) (PBT), a PC/PBT blend, modified poly(phenylene oxide), and a poly(phenylene oxide)/polyamide blend, have relative weld strengths of 45%, 26%, 76%, and 20%, respectively.     

Preparation and characterization of polyimide‐g‐nylon 6 copolymers from nonfunctionalized polyimides

In this research, the anionic polymerization of ?‐caprolactam was carried out in the presence of small amounts of several different polyimides to generate polyimide‐g‐nylon 6 copolymers. The polyimides, which were prepared from 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride and commercially available diamines with a one‐step method, were first dissolved in molten ?‐caprolactam. Phenylmagnesium bromide was then added at 120°C. Under these conditions, caprolactam anions were formed that attacked the five‐membered imide rings to form N‐acyllactam moieties, which activated the anionic polymerization of caprolactam. In essence, nylon 6 chains grew from the polyimide backbones. Probably because of a high activation energy, the process was relatively slow, requiring 1 h at 120°C. The introduction of 5 wt % polyimide into the graft copolymers produced significant increases in the tensile modulus and tensile strength in comparison with those of low‐ and high‐molecular‐weight nylon 6. The elongation to break, however, was reduced. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 292–299, 2006     

Thermoplastic vibration welding: Review of process phenomenology and processing–structure–property interrelationships

Vibration welding offers a robust method for physically joining thermoplastics to fabricate complex hollow assemblies from simpler injection‐molded articles without using an external heat source, adhesives, or mechanical fasteners. Vibration welding involves a complex interplay of several phenomena—solid (Coulomb) friction, melting, high strain‐rate, pressure‐driven, strong (high‐strain) melt flows, solidification, and microstructure development—which ultimately govern the strength and integrity of the weld. Defects in the weld region may lead to catastrophic failure of the welded assembly. In this article, the current understanding of the processing–structure–property relationships in the context of vibration welding of thermoplastics and polymer‐matrix composites is reviewed. Experimental as well as analytical methods of investigation of the vibration welding process phenomenology are presented. The interrelationships between the microstructure in the weld region and the resulting weld strength and fatigue behavior are then discussed in the light of this phenomenological information for neat polymers, filled polymers, polymer blends, and foams. This review is also aimed at identifying the areas requiring further investigation with regard to understanding vibration welding phenomenology and weld structure–property relationships. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Vibration welding of nylon 6 to nylon 66

Vibration welding of dissimilar nylons is a promising technique for assembling complex components made of different polymers. The effects of pressure and meltdown on the tensile strength of nylon 6 (PA 6) to nylon 66 (PA 66) vibration welds were determined in this study using an experimental design and three weld geometries. Weld strengths were generally improved by increasing meltdown and decreasing weld pressure. The weld strength was also shown to vary with the position of the lower melting material for T‐welds. Using differential scanning calorimentry and fracture surface analyses, it is concluded that for all geometries, higher weld strengths can be achieved when both materials are melted. Polym. Eng. Sci. 44:760–771, 2004. © 2004 Society of Plastics Engineers.     

Thickness effects in the vibration welding of polycarbonate

In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. Past work on welding characterized the effects of weld parameters such as the weld frequency, the weld pressure, and the weld time, on the welding process and weld strength, and showed that the most important parameter affecting weld strength Is the weld penetration—the decrease in the distance between the parts being welded that is caused by lateral outflow of material in the molten film. However, those weld studies were based on specimens of constant nominal thickness (6.35 mm, 0.25 in). This paper is concerned with the effects of specimen thickness on the weld process and weld strength.     

Effect of molding condition and pellets material on the weld property of injection molded jute/polylactic acid

Natural fibers such as jute fiber and biodegradable poly(lactic acid) (PLA) polymer are very good choices for environmental friendly material. Multi‐gate injection is often used to meet the demand of mass production of injection moldings, therefore weld line is inevitable. The presence of weld lines not only detracts from the surface quality but also significantly reduces the mechanical strength of injection‐molded parts. Although it is not always easy to completely eliminate weld lines, the weld strength could be improved through suitable adjustment of molding conditions such as melt temperature, mold temperature, hold pressure, injection speed, and so on. In this study, three kinds of pellets materials were prepared: long fiber pellets (LFT), the re‐compounding pellets (RP), and LFT50:RP50 hybrid mixtures (LFT/RP). Tensile test was carried out to investigate the effect of different pellets and holding pressures on the mechanical property of welded jute/PLA specimens. And the interfacial shear strength of non‐welded jute/PLA specimens was calculated with Kelly‐Tyson Formula. Fiber separation and fiber dispersion in RP became better than that of LFT which resulted in a better interfacial property. Weld strength of RP and hybrid LFT/RP specimens was improved by 43.34% and 16.46% than that of LFT specimen, respectively. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers