Repeated impact behavior of glass/epoxy laminates

The response of glass–epoxy composites to repeated impact for various impact energies ranging from 5 to 15 J was investigated. Specimens with two different stacking sequences were studied; [0/90/0/90]_S and [0/90/+45/−45]_S. In addition to the room temperature, impact tests were also performed at −40°C environmental test temperature for impact energy of 15 J. Contact force‐deflection and energy‐time curves at each test and the number of impacts to failure (N_f) were obtained for each experiment. Compression after impact (CAI) tests were also conducted to determine the residual load carrying capacity of the damaged specimens. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Influence of temperature on plane stress ductile fracture of poly(ethylene terephthalate) film

Abstract

Double edge notched poly(ethylene terephthalate) (PET) specimens of varying ligament lengths and 0·125 mm thickness have been pulled to complete fracture between 23 and 160°C. Within this temperature range, propagation of the crack was always stable, producing load–displacement curves at various ligament lengths that were geometrically similar to one another. Essential work of fracture (EWF) analysis was used to study the effect of temperature on fracture toughness. A linear relationship was obtained between specific total work of fracture W _f and ligament length over the entire temperature range under consideration. The slope of the line, which is termed specific non-essential work of fracture βw _p , showed a maximum near the glass transition temperature of the material (T _g ≈ 93°C). Beyond this point, βw _p decreased sharply with increasing temperature. The intercept of the line at zero ligament length, which is referred to as specific essential work of fracture w _e , showed three types of variation with respect to temperature. Below T _g , w _e was found to be more or less independent of temperature; above T _g it increased with temperature and reached a maximum value at the end of the leathery region (～120°C); beyond which it decreased steadily.     

Essential work of fracture evaluation of fracture behavior of glass bead filled linear low‐density polyethylene

The effect of the glass bead (GB) size and bead content on the fracture behavior of GB‐filled linear low‐density polyethylene (LLDPE) composites was evaluated by means of the essential work of fracture (EWF). The results indicated the specific EWF (w_e) is lower for the composites than that of pure LLDPE and the obtained w_e values do not show significant differences for the filled samples with different GB diameters. The non‐EWF or plastic work (βw_p) also decreased with the addition of GBs, indicating that less energy is absorbed during the fracture process for the composites filled with different diameter GBs. For the composites filled with GBs of different contents, the w_e decreased with increasing GB contents and the βw_p that was higher than that of pure LLDPE at relatively low contents also decreased with the content of GBs. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1781–1787, 2006     

Work of fracture of polystyrene/high density polyethylene blends compatibilized by triblock copolymer

The fracture toughening behavior of polystyrene/high density polyethylene blends compatibilized by 10 wt % of a styrene‐ethylene‐butylene‐styrene triblock copolymer (SEBS) was assessed using single‐edge notched tension (SENT) and double‐edge notched tension (DENT) specimens of various gauge lengths over a wide range of tensile rates. The fracture of DENT and SENT specimens was completely ductile under the plane‐stress condition. A linear relationship was observed between the specific total work of fracture and the ligament length (L) for a given L range. The results showed that the essential work (w_e) was independent of the tensile rate (R) range of 1–30 mm/min, and it then decreased considerably when R was increased to 50 mm/min and above. However, the nonessential work exhibited a rate independent trend behavior. In addition, w_e and the specific nonessential work of fracture (βw_P) were basically independent of the gauge length (G), provided that G was greater than the width of the sample. Finally, it was also shown that the w_e and βw_P values for SENT specimens are obviously greater than those for DENT specimens. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2074–2081, 2000     

Combined effect of temperature and thickness on work of fracture parameters of unplasticized PVC film

The combined effect of temperature and thickness on the essential work of fracture (EWF) parameters for an unplasticized poly(vinyl chloride) (uPVC) film was investigated using double edge notched tension specimens. It was found that for the range of temperatures (23°C to 60°C) and thicknesses (0.15 mm to 0.40 mm) studied here, specific essential work of fracture (w_e) was independent of temperature at each thickness but increased with thickness at each temperature. It was found that at each temperature, w_e and its yielding (w_e,y) and necking/tearing components (w_e,nt), all increased linearly with increasing thickness. However, whilet w_e showed no significant variation with respect to temperature, its yielding component (w_e,y) decreased and its necking/tearing component increased (w_e,nt) with increasing temperature. It was found that estimated values of w_e and its components w_e,y and w_e,nt via crack opening displacement values were by and large unsatisfactory, being either much higher or lower than the directly measured values.     

Fracture characterization of recycled high density polyethylene/nanoclay composites using the essential work of fracture concept

The effect of nanoclay on the plane‐strain fracture behavior of pristine High density polyethylene (HDPE) and recycled HDPE blends was studied using the essential work of fracture (EWF) concept. The failure mode of EWF tested specimens was found to be associated with the specific non‐EWF (β_Bw_p,B). Adding 6‐wt% of nanoclay to pristine HDPE and 2‐wt% to recycle‐blends greatly decreased the β_Bw_p,B values and led to a transition from ductile to brittle failure mode. A fractographic study revealed that the difference in failure modes was caused by the changes in micro and macro morphologies, which could be related with the specific EWF (w_e,B). In the ductile failure, w_e,B is governed by the fibril size; adding nanoclay and recycled HDPE to pristine HDPE decreased the fibril size and subsequently lowered the w_e,B value. In the brittle failure, the w_e,B value was enhanced by creating a rough fracture surface. Adding nanoclay to pristine HDPE, a steadily decrease in w_e,B was measured until 4‐wt% after which the change was insignificant. Conversely, nanoclay content more than 2‐wt% in recycle‐blends greatly decreased the w_e,B value. A transition map was constructed to illustrate the potential failure mode and the associated fracture morphology based on the tested material compositions. POLYM. ENG. SCI., 56:222–232, 2016. © 2015 Society of Plastics Engineers     

Temperature dependence of essential and non-essential work of fracture parameters for polycarbonate film

Abstract

Single edge and double edge notched polycarbonate specimens of thickness 0·;375 mm have been pulled to complete fracture at temperatures between 25 and 120°C. Within this temperature range specimens underwent full ligament yielding prior to final fracture, producing load–displacement curves at various ligament lengths that were geometrically similar to one another for a specific geometry. On the basis of these, the method of the essential work of fracture was used to study the effect of temperature on fracture toughness of polycarbonate film. Results showed that a linear relationship exists between specific total work of fracture w_t and ligament length L over the entire temperature range under consideration. The slope of the line, which is referred to as the specific non-essential total work of fracture βw_p , increased with increasing temperature. However, the interception at L = 0, which is referred to as the specific essential total work of fracture w_e , showed little variation with respect to temperature. Change of geometry affected both values, although the change in βw_p was more significant than that of w_e , for which change of no more than 10%was attained. Based on the maximum load on the load–displacement curve, w_t for double edge notched specimens was partitioned into the specific work of fracture for yielding w_y and the specific work of fracture for yielding necking/tearing w_nt . Linear relationships were found for both terms as a function of ligament length from which the essential (w_e,y , w_e,nt ) and non-essential (β_y w_p,y , β_{nt w p, nt} ) related work terms were attained. Results showed that the yielding related work terms for polycarbonate decrease, while the necking/tearing related work terms increase, with increasing temperature.     

Toughness assessment of elastomeric polypropylene (ELPP) by the essential work of the fracture method

The essential work of the fracture (EWF) method was employed to determine the fracture performance of thermoplastic polypropylene (PP) elastomers. Three types of elastomeric polypropylene (ELPP) of homo- and copolymer nature based on different catalysts were involved in this study. Tests were carried out in both I and III fracture modes to check the applicability of the EWF approach for such elastomers. It was found that the trouser tearing test (mode III) overestimates both the specific essential (w_e) and plastic work (w_p) terms when the tearing resistance of the ELPP is higher than the resistance to tensile loading. With decreasing crystallinity (i.e., by decreasing length of the stereoregular chain segments of the block copolymers or increased content of comonomer) w_e increased, whereas in respect to w_p,, an opposite tendency was found. This was interpreted by possible changes in the thermoreversible network structure of the ELPP in which crystalline domains act as network knot points in the amorphous PP matrix. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 873–881, 1998     

Essential work of fracture analysis of short glass fiber and/or calcite reinforced ABS/PA6 composites

The effect of reinforcing agent type and composition on the fracture behavior of short glass fiber (SGF), CaCO₃ particle, and glass fiber/CaCO₃ hybrid reinforced ABS/PA6 blend based composites have been studied by using the essential work of fracture (EWF) method. Two millimeter thick rectangular shaped samples were first processed in twin‐screw extruder and they were subsequently injection molded. Double edge notched tensile (DENT) specimens with various ligament lengths were subjected to tensile tests at 2 mm/min constant deformation rate at room temperature in order to determine EWF parameters. For the neat matrix and 10 wt% calcite reinforced materials fractured in ductile manner, that is, the ligament fully yielded and the crack stably propagated unlike the other compositions. For the neat matrix, both the specific EWF, w_e, and the nonessential work of fracture, βw_p, values dramatically decreased with increasing reinforcement weight ratio regardless of the agent type. The analyzing of yielding and necking/tearing components of essential and nonessential parameters showed that for the samples reinforced with SGF w_e,nt > w_e,y and β_ntw_p,nt > β_yw_p,y, indicating that a majority of fracture energy was dissipated in the necking and tearing stages of fracture process. POLYM. ENG. SCI., 54:540–550, 2014. © 2013 Society of Plastics Engineers     

EWF method to study long term fracture properties of cross‐linked polyethylene

The influence of cross‐linking on fracture properties of polyethylene has been studied by the method of essential work of fracture (EWF). Three distinct values of the cross‐link density were obtained by β irradiation with three distinct radiation doses, and characterized by sol‐gel and solvent swelling measurements. EWF tests were performed at speeds of 0.045 to 100 mm min^–1 at 80 and 110°C. The fracture toughness, as defined from the EWF method, is analyzed through essential (w_e) and nonessential (βw_p) components. Both values were found to be decreasing functions of the cross‐link density. But cross‐linking also suppresses the toughness decrease observed in linear PE at low speeds/high temperatures. It is hypothesized that cross‐linking prevents the chain disentanglement that occurs during crack growth. In conclusion, EWF tests performed at low speeds appear as an interesting method to characterize the influence of structural factors on the fracture properties of polyethylene. POLYM. ENG. SCI., 45:424–431, 2005. © 2005 Society of Plastics Engineers     

A quantitative analysis of the effect of interface delamination on the fracture behavior and toughness of multilayered propylene–ethylene copolymer/low density polyethylene films by the essential work of fracture (EWF)

The multilayered propylene–ethylene copolymer (CPP)/low density polyethylene (LDPE) composite sheets were prepared by the microlayered coextrusion system. The essential work of fracture (EWF) method was firstly used to quantitatively evaluate the fracture behavior of layered materials. The experimental results indicated that the two-dimensional layered interfaces in the multilayered materials could play an important role in the fracture behavior. The specific essential work of fracture, w_e, increased with the layers due to interfacial delamination. Additionally, the different testing speeds had a dual effect on the increscent trend of the specific essential work of fracture, w_e, with increasing layers.     

Impact specific essential work of fracture of compatibilized polyamide‐6 (PA6)/poly(phenylene ether) (PPE) blends

The essential work of fracture (EWF) method has aroused great interest and has been used to characterize the fracture toughness for a range of ductile metals, polymers and composites. In the plastics industry, for purposes of practical design and ranking of candidate materials, it is important to evaluate the impact essential work of fracture at high‐rate testing of polymers and polymer blends. In this paper, the EWF method has been utilized to determine the high‐rate specific essential fracture work, w_e, for elastomer‐modified PA6/PPE/SMA (50/50/5) blends by notched Charpy tests. It is found that w_e increases with testing temperature and elastomer content for a given specimen thickness. Morphologically, there are two failure mechanisms: shear yielding and pullout of second phase dispersed particles. Shear yielding is dominant in ductile fracture, whereas particle pullout is predominant in brittle fracture.     

Work of fracture of PBT/PC blend: Effect of specimen size,geometry, and rate of testing

Fracture behavior of PBT/PC blend was studied at room temperature using two specimen geometries (SENT and DENT) and a wide range of specimen sizes and crosshead speeds. It was found that the fracture of all SENT and DENT specimens is completely ductile and stable. A linear relationship was obtained between the specific total work of fracture, w_f, and the ligament length, L. Extrapolation of this linear relationship to zero ligament length gave the specific essential work of fracture, w_e, which for PBT/PC blend was 35 ± 5 kJ/m² and was almost insensitive to geometry and the dimensions of test specimens as well as testing rate.     

Effect of strain rate on the fracture toughness of some ductile polymers using the essential work of fracture (EWF) approach

The plane strain fracture toughness of two ductile polymers, ultra high molecular weight polyethylene (UHMWPE) and acrylonitrile‐butadiene‐styrene (ABS), was measured by using the essential work of fracture approach. Truly plane strain fracture toughness (w_Ie) was measured for ABS at quasi‐static and impact rates of loading. For UHMWPE, the measured values were only “near” plane strain values (w_Ie*). It was confirmed both w_Ie* and w_Ie were independent of specimen type but dependent on strain rate. For UHMWPE, there was a negative strain rate effect, i.e., w_Ie* decreased with increasing loading rate. At low quasi‐static loading rate (v = 10 mm/min), w_Ie* was constant at 55 kJ/m². It then decreased to 15 KJ/m² when the loading rate was increased to 100 mm/min, and remained at that value even up to impact rate of loading (v = 3.7 m/s). For ABS, a mild positive strain rate effect was observed. w_Ie increased from 13 kJ/m² at v = 10 mm/min to 17 kJ/m² at v = 3.7 m/s.     

Effects of gauge length and strain rate on fracture toughness of polyethylene terephthalate glycol (PETG) film using the essential work of fracture analysis

Essential Work of Fracture (EWF) analysis was used to study the fracture toughness of a PETG film. In the study of the gauge length (Z) effect on the specific essential work (w_e) using Z = 50, 100, 150, 200 and 250 mm, it is observed that w_e is Independent of gauge length, except that a slightly lower w_e value was measured for Z = 50 mm. Interestingly, for specimens with long gauge lengths (Z ≥ 150 mm in this study), brittle fracture occurred. The minimum ligament length at which ductile/brittle transition took place was observed to decrease with increasing gauge length. There is a small strain rate effect on w_e with loading rates less than 1 mm/min. But with higher loading rates, w_e showeld no strain rate sensitivity.     

Determination of fracture toughness of poly (ethylene terephthalate) film by essential work of fracture and J integral measurements

Abstract

The plane stress fracture toughness of a semicrystalline poly (ethylene terephthalate) (PET) film of thickness 0·125 mm has been measured as a function of specimen size, specimen geometry, loading rate, and temperature using the essential work of fracture (EWF) approach. It was found that the specific essential work of fracture w _e was independent of specimen width, specimen gauge length, and loading rate, but was dependent upon specimen geometry and test temperature. Below the glass transition temperature (93°C), w _e for double edge notched tension (DENT) type specimens was temperature insensitive, but increased with temperature for single edge notched tension (SENT) type specimens. The w _e value for SENT specimens was consistently higher than for DENT specimens. Estimation of w _e via crack opening displacement was reasonable using the relationship w _e = σ_n e _0,y; estimations made via similar type equations were either too high or too low and were generally unsatisfactory. It was found that values of J integral obtained by power law regression and linear extrapolation of the J–R curves to zero crack growth were lower than w _e. The power law regression of the J–R curves with ?a taken as half the crack opening displacement value at maximum load gave J _c values which agreed reasonably well with w _e.     

Change in the molecular weight distribution of poly(ethylene oxide) caused by the complexation with poly(acrylic acid)

The complexation between poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) was made by using double the molar quantity of either polymer component at pH 2 where the resulting complex completely precipitates. After the removal of the precipitate, PEO or PAA remaining in the supernatant was subjected to gel permeation chromatography to investigate the change in the molecular weight distribution (MWD) caused by the complexation. No remarkable difference is observed in the MWD curves for PEO[1] (M_w=1.37 × 10⁴) before and after the complexation with PAA[1] (M_w=1.10 × 10³) and PAA[2] (M_w=4.16 × 10⁵). However, the MWD curves of PEO[2] (M_w=1.26 × 10⁵) and PAA[2] become shortened and shift to the low molecular weight side after the complexation with PAA[1] or [2] and PEO[2], respectively. This tendency is enhanced by increasing the complexation temperature. From these results, it is indicated that the complexation between PEO and PAA deals with an equilibrium reaction, and the equilibrium constant is dependent on the chain length of both polymer components and also on the complexation temperature.     

Impact behavior of hybrid composite plates

This experimental study deals with the impact response of hybrid composite laminates. Two different hybrid composite laminates, aramid/glass and aramid/carbon, and two different stacking sequences, such as [0/0/90/90]_A+ [90/90/0/0]_G for AG1 and [0/90/±45]_A+ [±45/90/0]_G for AG2 and so on (see Table I ), were chosen for impact testing. The impact energy was gradually increased until complete perforation took place, and an energy profiling method (EPM) was used to identify the perforation thresholds of composites. The damaged samples were visually inspected. The images of the several samples subjected to various impact energies were registered and used for comparison and identifying damage mechanisms. The perforation thresholds for [0/90/±45]_s aramid/glass and aramid/carbon laminates were found to be approximately 5% higher than those for their counterparts with the [0/0/90/90]_s stacking sequence. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of injection molding–induced morphology on the work of fracture parameters in rubber-toughened polypropylenes

The effects of the injection-molding induced skin-core morphology on the fracture behavior of rubber-toughened polypropylene (RTPP) systems were studied by employing the essential work of fracture (EWF) method. RTPP with 31 wt% ethylene/propylene rubber (EPR) showed no skin-core structure after molding and the EWF approach worked well in this case. In contrast, RTPP with 10 wt% EPR exhibited a pronounced skin-core morphology: EPR deplection and enrichment was observed in the skin and core region, respectively. This morphology caused necking instead of crack growth in deeply double edge-notched (DDENT) specimens under tensile loading along the filling direction (MFD). The necking process not only was accompanied by a large scatter but also yielded highly unrealistic specific essential work of fracture (w_e) values. This skin-core structure was also the reason for an anistropic EWF response of this system observed by loading the specimens both in longitudinal (L) and transverse (T) directions to the MFD. The failure sequence and its characteristics were studied by light microscopy (LM) and infared thermography (IT). It was concluded that the EWF approach cannot be applied for RTPP with a prominent skin-core structure. Since yielding preceded the limited crack growth prior to necking in the loading directin for the DDEN-T specimen of RTPP with 10 wt% EPR, the yielding-related specific essential work (w_e,y) was used for toughness comparison. In case of RTPP with 31 wt% EPR, where yielding was less pronounced prior to the crack growth, the work of fracture until the maximum load was assigned to the yielding-related work of fracture (w_f,y) used for computing w_e,y. The latter value seems to be closely matched to the plane-strain essential work of fracture value.     

Fracture of polybutylene terephthalate (PBT) film

Combined effects of thickness and temperature on essential work of fracture (EWF) of polybutylene terephthalate (PBT) film were studied using single edge notched tension (SENT) and double edge notched tension specimens. It is found that specific essential work of fracture (w_e) for PBT is independent of temperature below T_g (≈80 °C), but decreases above T_g. Between temperatures 25 and 100 °C, w_e was independent of film thickness in the range 0.125-0.375 mm. The specific non-essential work of fracture (βw_p) was temperature and thickness dependent, being greater for the SENT type specimens. Specimen orientation had no influence on w_e but strongly affected βw_p. It was found that βw_p is greater for cracks propagating normal to the extrusion direction as compared to the parallel direction.