The effect of dispersed paint particles on the mechanical properties of rubber toughened polypropylene composites

The influence of dispersed paint particles on the mechanical properties of rubber toughened PP was investigated. The matrix was basically a hybrid of PP, rubber and talc. Model systems with spherical glass bead filled matrix were also studied to examine the effect of filler shape and size. Properties like tensile strength, strain at break, impact strength, and fracture toughness were influenced by the dispersed inclusions. Tensile strength at yield decreased linearly according to Piggott and Leinder's equation. Strain at break decreased more drastically with paint particles than glass beads, revealing that irregularly shaped particles offered greater stress concentrations. The tensile strength and strain at break were less influenced by the size of paint particles whereas a slight decrease in the modulus values was observed with decreasing particle size. Impact strength and fracture toughness also decreased with increasing filler fraction. Lack of stress transfer between filler and matrix aided in reduction of impact strength. Decrease in fracture toughness was influenced by volume replacement and constraints posed by fillers. The size of paint particles had little effect on the impact strength and fracture properties at the filler concentration levels used in this investigation.     

碳酸钙增强聚丙烯复合材料的断裂韧性

介绍了J积分方法的概念、理论和方法,并应用参考国外文献建立的,积分测试方法,结合扫描电镜形态分析研究了碳酸钙增强聚丙烯复合材料的断裂韧性。结果表明,碳酸钙的加入使复合材料对裂纹起始和增长过程的阻力都有大幅度提高,聚丙烯基体发生较大幅度塑性形变屈服后取向牵伸吸收塑性能。刚性填料加入时所导致的基体应力集中及界面脱粘后的基体应力集中促进聚丙烯基体产生局部区域微观塑性牵伸被认为是断裂韧性提高的原因。     

Micromechanical interpretation of fracture toughness of particulate-filled thermoplastics

The toughness behaviour of particulate-filled thermoplastics is determined by different failure mechanisms in the plastic zone and fracture process zone in front of the macrocrack such as particle-matrix debonding, shear processes or crazing and fracture of matrix fibrils. Theoretical expressions describing the critical strain causing microcrack initiation as well as the critical crack opening and the criticalJ integral value for unstable crack initiation are derived on the basis of a micromechanical analysis. Matrix properties, particle diameter, filler content and phase adhesion are taken into account. Critical particle contents and diameters caused by matrix morphology are discussed. Model calculations are compared with experimental results from acoustic emission analysis and dynamic fracture mechanics tests on PS, PVC and HDPE filled with CaCO₃ or SiO₂ particles.     

Wear rate and fracture toughness of porous particle-filled phenol composites

We experimentally investigated the effects of filler volume fraction of the phenol composites filled with porous particles on the fracture toughness and the wear rate against a smooth metal surface under multi-pass condition. Porous particles, made from rice husks, of various volume fractions from 0 to 0.5 were added to phenol resin as carbon filler. For the reported results of adhesive wear under multi-pass condition, we correlated the bulk parameters associated with the fracture toughness to the wear rate. We found an empirical power–law relation between the reciprocal of the product of stress and strain at rupture in bending test and the wear rate with various filler volume fractions. We also proposed the modified mixture law of the wear rate by taking account of the area fraction of transfer layer, which can provide a good prediction of the filler volume fraction dependence.     

Effects of graphene nanoplatelets and graphene nanosheets on fracture toughness of epoxy nanocomposites

The effects of graphene nanoplatelets (GPLs) and graphene nanosheets (GNSs) on fracture toughness and tensile properties of epoxy resin have been studied. A new technique for synthesis of GPLs based on changing magnetic field is developed. The transmission‐electron microscopy and the Raman spectroscopy were employed to characterize the size and chemical structure of the synthesized graphene platelets. The critical stress intensity factor and tensile properties of epoxy matrix filled with GPL and GNS particles were measured. Influence of filler content, filler size and dispersion state was examined. It was found that the GPLs have greater impact on both fracture toughness and tensile strength of nanocomposites compared with the GNSs. For instance, fracture toughness increased by 39% using 0.5 wt% GPLs and 16% for 0.5 wt% GNSs.     

Failure processes in particulate filled polypropylene

In this paper the common degradation effect of silicon oxide filler on fracture strain and fracture toughness of isotactic polypropylene is investigated by analysing the failure processes in the composite material by microscopic methods. Experiments demonstrate that, although fracture of the polymer regions absorbs considerable energy by plastic deformation, void formation and cracking of the interface between the polymer and the filler usually requires very little energy. These weak interfaces do not resist cracking and are the cause of brittleness in particulate filled systems. The crucial parameters influencing the fracture data of the composite were found to be the volume fraction of the filler and the interfacial adhesion between polymer matrix and particles. As the interfacial fracture energy is usually much smaller than the polymer fracture energy, the composite toughness drops when filler is added. Using a model which describes the individual steps of crack formation and final fracture, an attempt is made to explain the decrease of crack resistance of the polymer matrix with increasing filler fraction and to calculate the fracture energy of the composite by introducing partial values of crack resistance of the matrix and the interface, respectively. In addition, it is discussed how a coarse spherulitic morphology of the matrix, as produced by isothermal crystallization from the melt, can modify this behaviour.     

Failure mechanics in ternary composites of polypropylene with inorganic fillers and elastomer inclusions

The effects of phase morphology, interfacial adhesion and filler particle shape and volume fraction on the fracture toughness of polypropylene (PP) filled with CaCO₃ or Mg(OH)₂ and ethylene-propylene elastomer (EPR) were investigated. Separation of the inorganic filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the inorganic filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved by using maleic-anhydride-grafted EPR (MEPR) to increase the inorganic filler-elastomer adhesion. The two limiting morphologies differed significantly in fracture toughness under impact loading at the same material composition. A model for a mixed mode of failure, accounting for the plane strain and plane stress contributions to the strain energy release rate,G _c, was used to predict the upper and lower limits forG _c for the two limiting morphologies over an interval of elastomer volume fractions,v _e, from 0–0.2 at a constant filler volume fraction,V _f = 0.3, and over the filler volume fraction from 0–0.4 at constant EPR content. The role of material yield strength in controlling fracture toughness has been described successfully using Irwin's analysis of plastic zone size. The presence of elastomer enhances both the critical strain energy release rate for crack initiation,G _c, and the resistance to crack propagation as expressed by Charpy notched impact strength for the two limiting morphologies. Satisfactory agreement was found between the experimental data and predictions of upper and lowerG _c limits.     

Effect of filler surface morphology on the impact behaviour of hydroxyapatite reinforced high density polyethylene composites

Instrumented falling weight impact tests have been carried out to characterize the impact behaviour of hydroxyapatite reinforced high-density polyethylene composite (HA-HDPE) in order to use this biomaterial in skull implants. The effects of HA filler surface morphology and volume fraction on the fracture toughness were studied, and fracture mechanism investigated. Impact resistance was found to be markedly improved by using a sintered grade HA filler with smooth particle surface instead of spray dried grade HA with rough surface. SEM examination of impacted fracture surfaces revealed that the improvement of impact resistance was due to the stronger interfacial bonding between smooth HA particles and HDPE polymer matrix compared with that between rough HA and HDPE, which results in more energy absorption during impact and hence better fracture resistance.     

Strength and toughness properties of two nitrogen alloyed stainless steels and their submerged arc weldments at cryogenic temperatures

Submerged arc weldments of the two nitrogen-alloyed stainless steels X2 CrNiN 18 10 (similar to AISI 304 LN) and X4 CrNiMoN 18 14 (similar to AISI 316 LN) welded with the fully austenitic filler metal X2 CrNiMnMoN 20 16 were investigated. Tensile, impact toughness and single-specimen J-integral tests at room temperature, 77 K and 4 K were performed. The strength of the materials increased whereas the impact toughness and the fracture toughness decreased with decreasing temperature. The toughness of the steel X4 CrNiMoN 18 14 was superior to that of X2 CrNiN 18 10, and for the austenitic weld a good combination of strength and toughness was also found. On the fracture surface of the compact tension specimens, a stretch zone was found, the width of which was reduced with decreasing test temperature. For all three materials at all three temperatures the critical values, JIc, of the J integral determined according to ASTM E 813 are approximately twice the respective values for the J integral at physical crack initiation determined according to the German specification DVM 002 using the width of the stretch zone. © 1998 Chapman & Hall     

Impact behavior of hydroxyapatite reinforced polyethylene composites

Hydroxyapatite particulate reinforced high density polyethylene composite (HA-HDPE) has been developed as a bone replacement material. The impact behavior of the composites at 37 °C has been investigated using an instrumented falling weight impact testing machine. The fracture surfaces were examined using SEM and the fracture mechanisms are discussed. It was found that the fracture toughness of HA-HDPE composites increased with HDPE molecular weight, but decreased with increasing HA volume fraction. Examination of fracture surfaces revealed weak filler/matrix interfaces which can debond easily to enable crack initiation and propagation. Increasing HA volume fraction increases the interface area, and more cracks can form and develop, thus decreasing the impact resistance of the composites. Another important factor for the impact behavior of the composites is the matrix. At higher molecular weight, HDPE is able to sustain more plastic deformation and dissipates more impact energy, hence improving the impact property.     

Influence of alloying elements and heat treatment on impact toughness of chromium steel surface deposits

By means of Charpy impact tests, the impact toughness of chromium steels (nominally, 5% and 14% chromium) has been evaluated after the surfacing process and postheating at 350, 450 and 550 ° C. It has been found that impact toughness is primarily affected by the ratio between the nickel and chromium contents of the filler metals. The amount of energy required for impact fracture increases as the nickel to chromium ratio increases from 0.01 to 0.29. A metallographic analysis has shown that the nickel: chromium parameter affects the impact toughness, in that a different microstructure is obtained as this ratio varies. A marked susceptibility to temper embrittlement has been noticed for all types of filler metals examined. All materials are embrittled by postheating at 450 ° C; for some of them, temper embrittlement also occurs at postheating temperatures of 550 ° C. A decrease in toughness results in a larger number of brittle-fracture regions on the impact fracture surfaces. The brittle regions were observed to proceed primarily by a cleavage rupture mechanism.     

Spritzgegossene kupfergefüllte Thermoplaste für die Erzeugnisentwicklung

Injection moulded copper filled thermoplastics for the product development The aim of this study is to characterise the application properties of particle copper filled thermoplastic polymers produced by extrusion and injection moulding. The influence of a filler concentration und filler form on the mechanical, electrical and thermal properties was investigated. A high shape freedom, a production potential and low energy costs by the manufacturing of the products open variegated alternatives to use of these materials in the electronic, auto, building as well as other industries.     

Fracture toughness of a welded duplex stainless steel

The present work includes fracture toughness testing on 30 and 50 mm thick duplex stainless steel 2205 (22% Cr, 5.5% Ni, 3% Mo, 0.15% N). Base metal and submerged arc weldments (SAW) at subzero temperatures have been tested using full size three point bending. The evaluation of the results has been carried out using J-integral calculations and correlations to Charpy impact values. It is shown that the temperature dependence of the fracture toughness can be described by a transition temperature curve, the master curve. The reference temperature was evaluated to −143 and −101 °C for base and weld material respectively.     

高填充聚丙烯材料的增强和增韧

研究了本室研制的柔性分子链界面改性剂包覆的高岭土（ｋａｏｌｉｎ）刚性粒子增韧的短切玻璃纤维（ＣＦ）增强的混杂复合方式，对聚丙烯／高岭土（ＰＰ／ｋａｏｌｉｎ）填充材料强度和韧性的影响。     

Fracture Characteristics of Frit Bonding through In-Situ Nano-Indentation Testing

Because frit bonding material is brittle, sudden impacts such as dropping may damage the bonding significantly. Strain-rate-controlled in-situ nano-indentation testing, which can determine localized material properties, was carried out on the frit-bonded specimen, especially on the frit bonding matrix and the filler. The results were compared with the drop-impact fracture behavior to understand the fracture characteristics. Mechanical properties at static condition or low strain rate did not show proper relationship with the fracture tendency of the drop tested result of the frit bonding. From the relationship between fracture toughness and the ratio of modulus/hardness, fracture characteristics at the drop impact situation could be estimated by the values at the high strain rate nano-indentation. The ratio between modulus and hardness on frit matrix showed close relationship with drop impact fracture. Though crack propagation path deflected at filler interface, filler property gave less influence on fracture tendency of drop impact fracture due to its small volume fraction. The properties of frit matrix were crucial to the fracture characteristics of the frit bonding.     

Mechanisms of particulate filled polypropylene finite plastic deformation and fracture

The plastic deformation and fracture of aluminium hydroxide filled polypropylene has been investigated. A transition between two mechanisms with an increase of the filler volume fraction has been observed. Below a critical filler volume content φcr ≈ 20 vol% (designated region 1) adhesive failure processes and polymer deformation in the neighbourhoods of different particles occur in an uncorrelated manner. Above this critical value (designated region 2) exfoliation along the surface of the initial portion of inclusions causes the formation of craze-like deformation zones transverse to the direction of the loading. The concentration of craze-like zones is essentially determined by the filler content and the level of interphase interaction which in turn depends on the particle size. In region 1 deformation occurs in a macro heterogeneous way with the formation and growth of a neck. The elongation to break decreases with an increase in the mean diameter of the filler phase. At φ>φcr composites, filled with small particles, fail in quasi brittle manner with the formation of a short and narrow neck. In contrast to the case for a small filler concentration, an increase of the inclusion size leads to an increase in the ultimate elongation and a tendency to macro homogeneous yielding. An explanation of the observed behaviour is proposed based on a change in adhesive failure conditions with filler content and size. This revised version was published online in November 2006 with corrections to the Cover Date.     

Dynamic mechanical,electrical and magnetic properties of ferrite filled styrene-isoprene-styrene

The dynamic mechanical, electrical and magnetic properties of highly filled magnetic polymeric composites containing 75 to 85 wt % barium ferrite in a thermoplastic elastomer matrix styrene-isoprene-styrene (SIS), are reported. The dependence of the properties on the volume fraction of the filler has been investigated. It is shown that the toughness and shore hardness of the composite may be correlated to its dynamic mechanical parameters. The use of coupling agents for surface treatment of ferrites has been shown to improve the magnetic properties of the composite due to better filler dispersion.     

Parameters determining the strength and toughness of particulate filled epoxide resins

The effects of such parameters as the filler volume fraction, particle size, aspect ratio, modulus and strength of filler, resin-filler adhesion and toughness of the matrix on the stiffness, strength and toughness of particulate filled epoxide resins have been evaluated. The mechanisms of deformation and rupture in these multiphase materials are discussed, illustrated byin situ mechanical tests in the scanning electron microscope.     

A study of the mechanical behaviour on fibre reinforced hollow microspheres hybrid composites

This paper presents the results of an investigation into the effects of hollow glass microsphere fillers and of the addition of short fibre reinforcements on the mechanical behaviour of epoxy binding matrix composites. Properties like flexural stiffness, compressive strength, fracture toughness and absorbed impact energy, were studied. The specimens were cut from plates produced by vacuum resin transfer moulding having a microsphere contents of up to 50% and with fibre reinforcement up to 1.2% by volume. The tests performed with unreinforced composites show that flexural and compressive stiffness, maximum compressive stresses, fracture toughness and impact absorbed energy decrease significantly with increasing filler content. However, in terms of specific values, both flexural and compressive stiffness and impact absorbed energy increase with microsphere content. The addition of glass fibre produces only a slight improvement in the flexure stiffness and fracture toughness, while increasing significantly the absorbed impact energy. In contrast, the addition of a small percentage of carbon fibres produces an important improvement in both fracture toughness and flexure stiffness, when hybrid composites with 0.9% carbon fibre are compared to unreinforced foam, but did not improved absorbed impact energy.     

The effect of filler particle size and orientation on the impact fracture toughness of a highly filled plasticized polymeric material

The effect of particle size and orientation on the inherent fracture toughness of a filled plasticized polymeric material has been determined by application of linear elastic fracture mechanics. Testing was caried out in a three-point bend mode under impact conditions. The material was a triple base gun propellant consisting of a matrix of nitrocellulose plasticized with nitroglycerine and filled with particles of nitroguanidine (NQ). The crystalline NQ was used in the “as-received” form of needles and in a “ground” state. The material containing as-received NQ consistently had a higher fracture toughness than the material with ground NQ, and the toughness was a maximum when the fillers were aligned perpendicularly to the fracture surface. The impact fracture toughness was found to be virtually independent of strain rate over the range from 3 to 90 sec⁻¹. Seven-perforated cylindrical grains of the material containing as-received and ground NQ crystals, and the grains were tested in a pneumatic gas gun and a Hopkinson bar apparatus. The grains containing the ground NQ have been shown to be generally less resistant to fracture than the grains containing as-received NQ.