The influence of various standard (ASTM, ISO) and experimental moisture conditioning methods on mechanical performance of injection molded nylon 6 is discussed as a result of an in-depth, comprehensive investigation.These methods covered a wide range for two basic process parameters for conditioning: temperature (from 23 to 100 C) and relative humidity (from 50% RH to water immersion). The variation of these parameters may result in significantly different moisture absorption rates, equilibrium levels and mechanical properties. The kinetics of mechanical performance and microstructure were evaluated prior to tests and during conditioning in this comprehensive analysis.The results from this investigation may provide comprehensive, up-to-date information and recommendations concerning accelerated nylon conditioning methods for test specimens and various molded parts, preselection of nylon based plastic for design, and prediction and optimization of mechanical performance.

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To support the fatigue design of the cyclically stressed plastics parts, such as automotive under-the-hood and exterior components, we analyzed the short-term and long-term mechanical performance (tensile strength, fatigue strength, and fatigue life) of short glass fiber reinforced polyamides PA 6 and PA 66. Comprehensive tension-tension fatigue tests were conducted with reference to the latest ASTM, ISO, and Japanese industrial standards for plastics, at temperatures from 4 0°C to 121°C. on materials aged at 121°C for 0, 100, 500, and 1000 h. Tests were conducted at a loading frequencyf = 5 Hz, stress ratio R = 0.1, and in a wide range of cycles to failure from 2 x lo3 to 2 X lo6. Without aging and for both PA 6 and PA 66, the highest fatigue strength or fatigue life was found at -40°C; it decreased significantly at 23"C, and decreased further at 121°C. The fatigue strength of PA 6 was found to be higher than that of PA 66 at -40°C. but the reverse was seen at 23°C.At 12 1°C. the fatigue strengths of PA 6 and PA 66 were virtually the same. Aging at 12 1°C improved the tensile strength of PA 6 and PA 66 as aging time increased from 100 to 1000 h, and this process seemed to be more influential for PA 6.

Optimization of welding for thermoplastic parts strongly depends on the material properties, part design, as well as the welding operating technology conditions. Laser transmission welding requires preferential deposition of energy and subsequent melting of the material in the interfacial zone. This is optimized when the laser beam is transmitted through the transparent part and absorbed by the adjoining part to be welded. Energy deposition can be controlled to some extent by adjusting laser parameters (power, choice of beam focussing optics, sweep rate etc.). The thermoplastic material properties may have the greater influence and need to be characterized for optimum material selection. Commercial nylon type materials cover a large array of compositions, which may affect the welding process. To guide selection of nylon based plastics for a range of applications we have measured the influence of specific factors such as fiber-glass, mineral filler, impact modifier content, additives, and color versions on the Near InfraRed (NIR) transmission properties. In a following paper (Part II) a1 we have related these findings to the mechanical performance of shear and butt joints produced under various laser welding technology conditions (laser beam power, welding speed, laser beam/spot diameter, clamp pressure, plastic color, etc.). Comprehensive results of this evaluation will assist designers and technologists in thermoplastics selection for laser welding applications. The purpose of this report is to increase the understanding of the plastics engineering community regarding the usefulness and possible applicability of laser transmission welding (LTW) technology for nylon made components.

A comparative study of the mechanical performance of welded polyamide joints is evaluated. Under optimized welding (linear and orbital vibration, hot plate, transmission laser) conditions, the tensile strength of welded polyamide/nylon (filled and fiber-reinforced) is close or slightly higher (up to 14%) than the tensile strength of the base polymer (non-filled polyamide). In this study, the influence of two important effects (local reinforcement and "memory") on the mechanical performance of polyamide/nylon welds is analyzed and discussed. The results presented in this study will help plastic part designers, material developers and manufacturers, choose optimized welding conditions for polyamide/nylon parts in a wide range of industrial applications. For a better understanding of the role and influence of the processing temperature of the melt (in injection molding) and weld-melt (in welding) on mechanical performance of semi-crystalline molded (welded) thermoplastics, we performed a comparative study for polyamide/nylon 6 and polyamide/nylon 66 (non-filled and fiberglass reinforced) plastics. Mechanical performance of injection molded and welded nylon was evaluated using static (tensile and flexural) and dynamic (impact, DMA) tests. The static (tensile and flexural) and dynamic mechanical (DMA) properties were evaluated at a wide range of end-use temperatures, typical for welded nylon parts in automotive under-the-hood, small engines for lawn & power, and similar applications. Melt temperatures (for an injection molding) were varied from 225 °C to 310 °C. These values are significant above (up to 87 0 C) to the melt point of nylon 6 (T mp = 223 °C). Presented results will help product developers, designers, technologist, and manufacturers, by given them suggestions on the optimized temperature conditions of a melt and weld-melt inter-phase area. Comprehensive studies of the mechanical performance of welded polyamide 66 with respect to plastic composition were published by H. Potente, M. Uebbing and E. Lewandowski [7]. A comparative study of nylon 6 and nylon 66 welded joints, influenced by temperature and moisture, was published by I. D. Froment [8]. D. Grewell, in a comprehensive study [9] for the orbital welding technology, repeatedly achieved similar [3] tensile strength for PA 6 joints. Presented in these studies [7-9] are results on mechanical performance of PA 6 and PA 66 joints were applied [10-14, etc.] in the design of vibration welded air intake manifolds (AIM), resonators, etc. Reported in [7-11] tensile strength data for welded joints are very similar for both plastics (PA 6 and PA 66) and is equal to 65-72 MPa (for 30-35 wt.% fiberglass reinforcement). Capron ® is a registered trademark of BASF Corporation.