Mechanical Impact Behavior Research Articles

Investigations of three-dimensional fiber orientation on mechanical impact behavior of short glass-fiber-reinforced PEEK composites

This work presents experimental and numerical investigations of three-dimensional (3D) fiber orientation on mechanical impact behavior of short glass-fiber-reinforced polyether ether ketone (SGFR PEEK) composites. The incorporation of short fibers significantly enhances the stiffness and strength of the composites while reducing the ductility, thereby, making the study of their impact response essential. To this end, we firstly manufactured the composite components using injection molding, and used the micro-computed tomography (µCT) to measure the fiber orientation distribution in 3D space for mechanical behavior prediction. Then, by studying the molded components across the thickness based on the actual observation, a distinct laminate structure with seven layers was quantitatively evaluated. A representative volume element (RVE) micromechanical computational method was developed and compared with the experimental results. Furthermore, homogenization method with the periodic boundary condition was implemented to evaluate the effective mechanical properties of the molded components. Finally, the phenomenological Johnson Cook (JC) model with fracture behavior was conducted to analyze the impact response of the injected components with different fiber orientation distributions. The new framework is demonstrated by acceptable energy absorption capability prediction of the SGFR PEEK composites.

Comparison of lightning strike behavior between carbon fiber reinforced materials with thermoset resin matrix and thermoplastic resin matrix

One of the weak points of the structures made of carbon fibre reinforced materials and thermosetting matrix is its mechanical impact behavior. In order to improve it, materials reinforced with carbon fiber and thermoplastic resin matrix are under study. In addition to the mechanical properties there are other factors to consider before introducing any structural material in the manufacturing of an aircraft, such as its lightning strike behavior. Materials properties that influence this behavior are mainly electrical, thermal and also mechanical; and these properties are modified from thermoset resins to thermoplastics. Within the Clean Sky program Airbus Defense and Space has carried out preliminary tests on flat panels manufactured by Fidamc with a carbon fibre reinforced material and thermoplastic resin matrix with two different configurations, both layout and additional (with and without metallization) The tests objective was the evaluation and comparison of the damages obtained after a lightning strike in flat panels made of traditional materials (thermoset matrix) with those made with new thermoplastic matrix materials. Both the mechanical damage and the temperatures generated in the material (using a thermal camera during the test) were analyzed in order to compare the thermal behavior of the thermoplastic matrix against the thermostable. This article shows the work done as well as results and conclusions.

Microstructure and Mechanical Impact Behavior of Ultra-Low Carbon Microalloyed Pipeline Steel Used in Chemical Pipeline during Welding Heat Treatment with Computer Aid

Through optical microscopy, scanning electron microscopy, transmission electron microscopy and impact testing machine and other equipment, this paper study the microstructures and impact properties of ultra-low carbon microalloyed pipeline steel. The results show that the base metal of ultra-low carbon microalloyed pipeline steel is mainly composed of granular bainite and bainite ferrite. The coarse grain structure of HAZ in welded joints mainly includes bainite ferrite, granular bainite, a small amount of polygonal ferrite and fine M-A island, and the grain size is coarse. The acicular ferrite in the weld is mainly induced by complex oxides of titanium, aluminium, silicon and manganese. And the organizational structure is interlaced with the basket weaving structure. The microstructures of weld zone and heat affected zone of ultra-low carbon microalloyed pipeline steel are obviously different.

Low temperature effect on impact energy absorption capability of PEEK composites

This paper describes the results of an experimental investigation which analyses the impact behavior at low temperature of polyether–ether–ketone (PEEK) and its short carbon fiber reinforced composite (SCFR PEEK). These polymer materials are widely employed in aeronautical applications subjected to impact loadings in which the energy absorption capability is an aspect that should be taken into account. The energy absorption capability can drastically decrease if temperatures near to the ductile-to-brittle transition temperature of polymeric matrix are reached. In this work, a set of perforation tests has been conducted covering a testing temperature range from −75°C to +25°C and an impact kinetic energy range from 11J to 175J, including typical values considered in impact loadings at aeronautical flight speeds. Energy absorption capability, damage extension and failure mechanisms have been quantified and reported. At low temperatures, a ductile-to-brittle transition was found in PEEK unfilled resulting in a suddenly change of its mechanical impact behavior affecting the energy absorption capability. In case of SCFR PEEK composite, a brittle behavior was observed for the whole temperature range considered and its energy absorption capability decreases drastically at lower temperatures. The brittleness of PEEK and SCFR PEEK at low temperature will limit the application of this composite in aeronautical structures exposed to impact.

Investigation of mechanical impact behavior of short carbon-fiber-reinforced PEEK composites

This paper describes the results of an experimental and numerical investigation of the impact behavior of short carbon fiber reinforced polyether-ether-ketone (SCFR PEEK) composites. The biocompatibility of PEEK and its short fiber composites, their rapid processing by injection molding and suitability for modern imaging have supported technological advances in prosthetic implants used in orthopedic medicine. Surgical implants, including hip and cranial implants, can experience clinically significant impact loading during medical installation and useful life. While the incorporation of short fibers in a thermoplastic matrix can produce significant improvements in stiffness and strength, it can also cause a marked reduction in ductility, making study of their energy absorption capability essential. In this work, the mechanical impact behavior of PEEK composites reinforced with polyacrylonitrile (PAN) short carbon fibers 30% in weight is compared with unfilled PEEK. The perforation tests conducted covered an impact kinetic energy range from 21J to 131J, equivalent to the range observed in a fall, the leading cause of hip fractures. Energy absorption capability, damage extension and failure mechanism have been quantified and reported. A numerical modeling that includes homogenization of elastic material and anisotropic damage is presented and validated with experimental data. At all impact energies, SCFR PEEK composites showed a brittle failure and their absorption energy capability decreases drastically in comparison with unfilled PEEK.

Mechanical impact behavior of polyether–ether–ketone (PEEK)

This paper deals with the mechanical behavior of polyether–ether–ketone (PEEK) under impact loading. PEEK polymers are the great interested in the field of medical implants due to their biocompatibility, weight reduction, radiology advantage and 3D printing properties. Implant applications can involve impact loading during useful life and medical installation, such as hip systems, bone anchors and cranial prostheses. In this work, the mechanical impact behavior of PEEK is compared with Ti6Al4V titanium alloy commonly used for medical applications. In order to calculate the kinetic energy absorption in the impact process, perforation tests have been conducted on plates of both materials using steel spheres of 1.3g mass as rigid penetrators. The perforation test covered impact kinetic energies from 21J to 131J, the equivalent range observed in a fall, an accidental impact or a bike accident. At all impact energies, the ductile process of PEEK plates was noted and no evidence of brittle failure was observed. Numerical modeling that includes rate dependent material is presented and validated with experimental data.

Measurement techniques and preliminary results of drop tests with full scale spent fuel transport and storage casks

The experimental testing and quantitative stress analysis of new cask designs becomes more and more important with increasing size of casks and their impact limiters, in order to assess the safety margins as well as for calculation validation reasons. Full scale drop testing of spent fuel transport and storage casks is performed by the Federal Institute for Materials Research and Testing within the type B package approval procedure and for safety demonstration reasons respectively. In drop tests for demonstrating ability of a package to withstand normal and accident conditions of transport, the instrumentation of a specimen is an important tool to evaluate its mechanical behaviour during impact. Generally, the instrumentation incorporates the measurement of strains and accelerations at the package. Test results as deceleration–time and strain–time functions constitute a main basis for the validation of assumptions in the safety analysis, for the evaluation of calculations based on finite element methods and extrapolation of scale model testing on full sized package within approval design tests. Besides, all of the above mentioned instrumentation, the flatness of the sealing area and the circularity of the cask lid flange are determined by using three-dimensional coordinate measurements to evaluate the mechanical impact behaviour of the cask flange region after the drop test sequence. Indispensable are measurements concerning leak tightness of the closure lid system. Additionally, specific photogrammetric measurements are used to characterise the conditions of the closure lid system after drop test in more detail. The preparation and interpretation of the results is in progress and indicates possible correlations between the leak tightness rate and measures of the relative movement of the lid.

Considerations of the Competent Authority Concerning the Assessment of a Brittle Fracture Safe Ductile Cast Iron (DCI) Cask Design

AbstractThe assessment of a brittle fracture safe ductile cast iron (DCI) cask design must ensure the integrity of transport and storage casks for radioactive materials under the most damaging accident conditions. Based upon the determination of the mechanical impact behaviour and stress analysis, for cask design sufficient material properties like fracture toughness must be ensured in series cask production by accepted quality assurance measures. The current BAM safety assessment concept has been established in the 1980s and is mainly based upon approval design tests with large cylindrical CASTOR and TN casks equipped with impact limiters. This concept needs only a reduced fracture mechanics analysis because of stress limitation at a level of approximately 50% of materials yield strength and appropriate quality assurance measures which ensure only tolerable crack-like defects within the cask structure in connection with guaranteed fracture toughness down to −40°1C. In other cases a detailed fracture mech...