The effect of loading rate on the fracture toughness of fiber reinforced polymer composites

This article is a detailed review of the strain rate dependence of fracture toughness properties in polymer composite materials. An attempt is made to draw together all the strain rate studies done in the past and to elucidate the reasons given by the authors of the reviewed papers for the trends resulting from their studies to better understand the strain rate effects on the fracture toughness of fiber reinforced polymer composite materials. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 899–904, 2005     

Assessment of temperature-dependent fracture behavior with different fracture mechanics concepts on examples of unoriented and cold-rolled polypropylene

Applicability of different fracture mechanics concepts, including linear elastic fracture mechanics (LEFM), equivalent energy concept, and elastic-plastic fracture mechanics (EPFM), to assessing the temperature-dependent fracture behavior was compared using examples of an unoriented and a cold-rolled polypropylene under quasistatic and under dynamic loading. Under quasistatic loading, the fracture toughness values were determined from the recorded load versus load-line displacement curves on compact tension (CT) specimens. Fracture toughness values under dynamic loading were determined from the recorded load versus deflection curves on single edge-notched bend (SENB) specimens. In spite of its simplicity as an engineering design parameter, on the basis of the LEFM concept, the stress intensity factor K can only be validly used in a limited temperature range. Instead, the EPFM parameters (i.e., the J integral and the crack opening displacement (COD) concepts) can be applied over a wider temperature range. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1237–1249, 1997     

Dynamic failure and inelastic deformation behavior of SiC ceramic under uniaxial compression

The investigation of the dynamic compressive properties and failure process of ceramics can broaden their applications under extreme conditions. In this study, the online dynamic deformation and failure processof silicon carbide (SiC) ceramic were directly observed in the split-Hopkinson pressure test by high speed photography. The failure strength of the silicon carbide has been quantified as a function of strain rate. There appears to be a critical value (a transition strain rate), above which the strain rate dependency becomes significant. The failure in the dynamic test is an outcome of the concurrent incline major crack and longitudinal micro-cracks. Scanning electronic microscopy (SEM) observation of the dynamic fragments shows that the transgranular fracture dominates the failure process. High-resolution transmission electron microscopy (HRTEM) observation of the post-collected fragments indicates that the local shear stress causes the nucleation of dislocations responsible for the macroscopic inelastic deformation behavior.     

Effect of high loading rate and low temperature on mode I fracture toughness of ductile polyurethane adhesive

The mode I fracture toughness of an adhesive at low temperatures under high loading rates are studied experimentally. Typical R-curves of the polyurethane adhesive under different loading rates (0.5?mm/min, 50?mm/min, 500?mm/min) at different temperatures (room temperature, ?20?°C, ?40?°C) respectively are obtained. From the experimental results, the mode I fracture toughness of this adhesive is extremely sensitive to the high loading rates and low temperatures. With the increase of the loading rate and decrease of temperature, the mode I fracture toughness of this adhesive decreases significantly. Under the loading rate of 500?mm/min at ?40?°C, the mode I fracture toughness of adhesive is 15% of the value at room temperature (RT) under quasi-static conditions. Through the experiment, the relationship between mode I fracture toughness of this adhesive, nominal strain rate and temperature is obtained.     

Analysis of the fracture process zone and effective crack length in the adhesively bonded end-notched flexure specimen

The mode II fracture of adhesive joints is well-known to involve large fracture process zones. Their effect in fracture energy measurements can be taken into account by the effective crack length approach. Moreover, fracture process zones can be simulated by cohesive zone models, which are increasingly used for structural analysis of adhesive joints. This paper aimed at evaluating the influence of the traction-separation law on the fracture process zone and on the effective crack length in end-notched flexure tests. Novel analytical cohesive zone models were developed for the bilinear and trapezoidal traction-separation laws. The latter were shown to affect significantly the energy dissipation rate versus effective crack length curve prior to crack initiation. Therefore, this effect seems to provide a simple approach for evaluating approximate traction-separation laws. The models here developed are easy to apply and provide simple approximate expressions useful for specimen selection.     

Effects of temperature and strain rate on the tensile behavior of polypropylene composites insulator coatings used in offshore deepwater pipelines

Polypropylene (PP) composites are being increasingly used as thermal insulation coatings in both onshore and offshore pipelines. In this study, the direct tensile behavior of pure PP, PP with glass microsphere filler, and PP with 65% glass filler were investigated at 22, 60, and 90 °C temperatures at various strain rates from 0.003/min to 0.300/min. Fourier transform infrared spectroscopy and scanning electron microscope studies were used to characterize the materials. Stress–strain relationships of the materials were nonlinear in the elastic and inelastic domains. Addition of glass fiber to the PP increased the elastic modulus, but the yield strength and yield strain were reduced along with the ductility. Based on the experimental results, constitutive models coupling the strain rate and temperature have been developed to predict the yield strength, the initial elastic modulus and secant modulus at yield for the PP composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45209.     

Effect of molecular structures on static and dynamic compression properties of clay and amphiphilic clay/carbon nanofibers used as fillers in UHMWPE/composites for high-energy-impact loading

Three different ultrahigh-molecular-weight polyethylene (UHMWPE)–clay nanocomposites (Muscovite, Cloisite 30B and amphiphilic clay/carbon nanofibers) were investigated with the nanocomposite nanomorphology studied before and after dynamic mechanical compressive tests at high strain rates. Their material structure and thermal properties were investigated using techniques such as step-scan differential scanning calorimetry, split Hopkinson pressure bar, synchrotron small angle X-ray scattering (SAXS), and dynamic mechanical analysis. Results were associated with morphological changes observed after deformation. chemical vapor deposition (CVD)-modified nanocomposite, due to the molecular bonding and the extra functional groups, is designed with crystalline structures with fewer defects and higher stability. The increase in particulate/polymer interactions observed for the CVD-modified material decreased the elongation in the quasi-static test. However, the dynamic mechanical behavior contradicted the quasi-static behavior because at very high strain rates there was not sufficient time for the interlamellar and intralamellar defect facilitated plastic flow and the material transitioned through the glassy state. The SAXS results show that deformation strongly induced changes in the UHMWPE and UHMWPE–clay nanocomposite morphology. SAXS indicates that CVD-modified samples became more compact and dense, thus corroborating the formation of additional secondary bonds between structures and/or the carbon nanofibers alignment. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47094.     

矿石回收率与贫化率关系的实验研究

分析了非均匀散体在放矿吕的流动特点，通过模拟试验，查明了放矿过程中矿岩接触面在下移过程中，矿，岩颗粒的掺杂情况，以及在多分段放矿过程中矿石回收率与贫化率之间的关系。