Influence of EPS bead fusion on pattern degradation and casting formation in the lost foam process

The effects of bead fusion in the pattern on foam degradation and on casting formation have been studied. Injection molded ASTM D638 tensile specimens have been used to develop a microscopic technique to quantify the extent of bead fusion in the pattern. The tensile properties of the polymer have been correlated with the measured degree of bead fusion. A variety of experiments have been conducted to highlight the effects of fusion on foam degradation. The flow behavior of a molten aluminum alloy has been studied in patterns with various levels of fusion. The results indicate that the degree of fusion has a significant effect on bead collapse and viscous residue formation in the polymer. The mold fill times generally increase with increasing bead fusion in the pattern. The temperature at the metal front drops more rapidly as the bead fusion increases.     

EPS molecular weight and foam density effects in the lost foam process

The effects of pattern molecular weight and density on casting formation in the lost foam process have been studied. The tensile properties of injection molded ASTM D638 tensile rods have been measured for various densities and molecular weights. Thermogravimetry, differential scanning calorimetry and other techniques have been used to study the thermal degradation characteristics of the pattern. A thermometric technique has been used to study the mold filling behavior with aluminum alloy A356. The results indicate that the tensile properties in the foam generally improve with increasing molecular weight and density. The structural characteristics of the foam may have a greater influence on mechanical properties than molecular weight. The rate of volatilization of the polymer increases as the weight average molecular weight, M _w, is lowered from 304,000 g/mol to 152,000 g/mol. The mold fill time increases with pattern density and M _w. The data suggest that pattern density and molecular weight may have a significant effect on the quality of the casting.     

EPS bead fusion effects on fold defect formation in lost foam casting of aluminum alloys

The effects of bead fusion in the polymer pattern on fold defect formation in castings produced by the lost foam process have been investigated. Castings of aluminum alloy 319.1 were produced with commercial patterns that were molded with varying levels of bead fusion. Each casting was broken into over 40 pieces to identify the fold defect on the fracture surface. The results indicate that castings produced with patterns with high bead fusion exhibit a greater number and a larger area of folds than parts obtained by using foams with low bead fusion.     

Local stiffness-density correlations for polycarbonate structural foams

Most studies on the mechanical properties of foams have focused on correlating pointwise, through-thickness elastic modulus and density variations. These local property correlations have then been used to predict the tensile and flexural moduli of foam bars. However, there is some question as to the meaning of a pointwise local density for a cellular material, and the dependence of local modulus on the local density is difficult to measure. This paper is concerned with correlating the density and tensile moduli of structural foams over a 12.7-mm scale. Data obtained from tests on 6.35-mm- and 4-mm-thick polycarbonate foam plaques, molded at nominal density reductions of 5, 15 and 25%, are used to show that the local average tensile modulus of the material correlates linearly with the local average density of the material.     

Experimental investigations for improving part strength in selective laser sintering

Selective laser sintering (SLS) is a powder-based rapid prototyping process in which parts are built by sintering of selected areas of layers of powder using laser. Nowadays, SLS is emerging as a rapid manufacturing technique, which produces functional parts in small batches, particularly in aerospace application and rapid tooling. Therefore, SLS prototypes should have sufficient strength to satisfy functional requirements. Apart from the energy density which is the combination of laser power, beam speed and hatch spacing, various other parameters like refresh rate, layer thickness and hatch pattern influence part strength. In the present work, relationship between strength and the various process parameters namely layer thickness, refresh rate, part bed temperature and hatch pattern have been investigated. Experiments are conducted based on Taguchi method using L₁₆ modified orthogonal array. Tensile specimens of polyamide (PA2200) material as per the standard ‘ASTM D638’ are fabricated on SLS machine with constant energy density and tested on a universal testing machine for tensile strength. Optimum strength conditions are obtained by maximising signal to noise (S/N) ratio and analysis of variance (ANOVA) is used to understand the significance of process variables affecting part strength. A regression model to predict part strength has been developed. Confirmation test conducted subsequently has revealed that the results are within the confidence interval.     

Influence of lustrous carbon defects on the fatigue life of ductile iron castings using lost foam process

Ductile cast irons are technologically important materials and are used extensively in automotive industry. Defects produced during casting process often play a dominant role in limiting mechanical properties and fatigue life under cyclic loading in cast alloy components. In order to investigate the effects of process induced defects on the fatigue behavior, in this paper two batches of ductile iron specimens cast using green sand and lost foam molding processes were studied. The ductile irons produced by lost foam molding generally were characterized to have lustrous carbon defects which left from the foam material. To evaluate the effect of lustrous carbon defects on fatigue performance of lost foam molded specimens, experimental fatigue tests were conducted on the both batches of ductile cast iron specimens to obtain S–N data. These data were used to compare fatigue performance of two batches of specimens. The lost foam molded specimens obviously exhibit lower fatigue life i.e. lower S–N curve than green sand molded specimens. Also, the fatigue life of lost foam molded specimens were predicted using AFGROW software, which works based on linear elastic fracture mechanics (LEFM), by assuming lustrous carbon defects as cracks in which they grow until final fracture under cyclic load. The predicted fatigue lives were compared with the experimental ones.     

Fiber-reinforced composite foam from expandable PVC microspheres

The properties of composite foam based on PVC expandable microspheres reinforced with continuous aramid fibers are described. The foam was fabricated by infiltrating low-density non-woven fiber webbing with PVC microspheres. The assembly was subsequently heated to expand the foam. The resulting composite foam consisted of 10 wt% aramid fibers and had a density of 100 kg/m³. Mechanical properties, crack propagation, and microstructure of composite foams were evaluated and compared with properties of similar unreinforced foam and with commercial PVC foam of comparable density. The influence of fiber concentration, fiber architecture and bonding was investigated also. Properties were measured in tension, shear, compression, and flexure using standard ASTM test methods. The composite foam performance equaled or surpassed the performance of most thermoplastic foams commercially available. The tensile strength and modulus of the composite foam increased by factors of 6 and 8, respectively, and the shear strength and modulus increased by factors of 1.8 and 2.4. The composite foam also exhibited improved strain energy density and damage tolerance, and reduced notch sensitivity.     

The adaptive slicing algorithm and its impact on the mechanical property and surface roughness of freeform extrusion parts

In the process of fused deposition modelling, the layer thickness plays a vital role in determining the surface quality and forming time. If a larger layer thickness is adopted, the molding time will be shorter, as a result, the surface accuracy of the product will be worse at the same time. If a smaller thickness is used, the surface quality of the product can be guaranteed, but the molding time will be very long accordingly. Therefore, there exists conflict between guaranteeing the surface quality and shortening the forming time of the part. This paper adopts adaptive slicing algorithm to solve this conflict. According to the curvature of the model, an appropriate thickness value is adopted automatically where the model curvature is large, a smaller thickness value is necessary, on the contrary, a larger thickness value is used. The tensile strength experiment was made through the specimens of ASTM D638 to study the influence of layer thickness. The temperature of the first six layers in the processing of building was collected. The ultra-depth picture of the cross-sectional area showed that the temperature would affect the neck length between adjacent filaments. Moreover, the surface roughness of the cylinder with different layer thicknesses was measured and the Ra curve figures showed the surface roughness was also influenced by layer thickness. The experiment results suggested the layer thickness was a critical factor in determining mechanical property and surface roughness by changing the layer counts and the neck length between adjacent filaments. It can be noted from the experiments that the adaptive slicing algorithm was not only good at enhancing the surface accuracy and tensile strength, it could also improve the building efficiency.     

改性PET的微孔注塑成型

采用均苯四甲酸二酐(PMDA)扩链增粘改性后的聚对苯二甲酸乙二醇酯(PET)(M-PET)进行Mucell微孔注塑成型实验。扫描电镜(SEM)结果表明,M-PET具备了维持良好泡孔形态所需的熔体强度,其微孔注塑制品分为皮层、中间层与芯层三部分。通过正交实验和信噪比(S/N)分析法,考察了M-PET在微孔注塑成型过程中各重要操作参数对制品拉伸强度的影响。研究结果表明,高的熔胶量,适中的发泡剂含量和熔体温度,以及较低的射胶速率和模具温度有利于提高制品的拉伸强度,在各操作参数中,熔胶量对制品拉伸强度影响最大。获得了发泡样条力学性能与减质量之间的关系。     

Characterization of a peek composite segmental bone replacement implant

A composite material of polyetheretherketone and short, chopped E-glass fibers was used to produce a segmental bone replacement implant. Problems with current metallic implants include stress-shielding of the surrounding bone and subsequent loosening of the implant. A better match between the bulk material properties of the implant and the bone it replaces can decrease the occurrence of these problems. Composite materials were chosen because their properties can be tailored to match the requirements. Material selection was accomplished with the aid of modeling software, which predicted the composite properties based on its composition and fiber directional parameters. Prototype parts were completed through a series of in-house molding and machining processes. Sections complete with an embedded metallic porous surface were tested to measure the strength of the attachment of the surface. The molded parts were characterized both destructively and nondestructively. The results of tensile tests performed on molded parts were comparable to those using commercially supplied samples. The fiber orientation was measured to verify the random positioning of fibers throughout the part, as assumed in the initial material selection. Ultrasonic C-scanned images confirmed that the molded parts had a very low density of air pockets or voids.     

聚丙烯分子量对其注射成型试样的拉伸和抗冲特性的影响

通过对聚丙烯及其经化学降解后的一系列不同分子量聚丙烯的注射成型样条的密度、结晶度、形态、取向、常温拉伸特性和低温抗冲性等方面的实验,讨论了分子量对这些性能的影响。分子量对密度、结晶度影响不大,但对形态及内外层的取向结构影响较大,而低温抗冲性能随分子量下降较多,常温抗拉特性随分子量变化较复杂,就其综合性能而言,以分子量在某一范围内较好。     

Crack growth resistance curves of GLARE 3 5/4 0.3 fiber–metal laminates at low temperature

The objective of this work was the evaluation of crack growth resistance curves ( J–R curves) of commercial GLARE® 3 5/4 laminates at −50 °C. The experimental evaluation of these curves was performed on 50‐mm‐wide compact tension specimens through the unloading compliance technique. The tests were based on the ASTM E1820 standard with minor modifications. Additionally, tensile tests were also performed at −50 °C on dogbone specimens according to the ASTM E8M standard. Comparisons between low and room temperature properties indicate that the material preserves both its tensile strength and fracture toughness at −50 °C, although low temperature J–R curves presented smaller slopes than the room temperature ones after the onset of stable crack growth.     

Direct observation and measurement of fiber architecture in short fiber-polymer composite foam through micro-CT imaging

A non-destructive X-ray imaging technique was used to determine internal structure in a polymer foam reinforced with short fibers. The technique, known as micro-CT (for computerized tomography), was used to measure the fiber length distribution (FLD) and fiber orientation distribution (FOD), two parameters that are critical to the behavior of short-fiber-reinforced composites. Phenolic foam reinforced with short glass fibers was used as an exemplar to demonstrate the potential of this technique, exploiting the large difference in density between the two components. Direct 2D and 3D images were generated in which individual fibers were clearly resolved, along with portions of the foam structure. The images were analyzed using computer software to obtain quantitative FLD and FOD data. A distinct preferred orientation of fibers was revealed that was attributed to shear flow during foam expansion. For quantitative analysis of microstructure in short fiber composites, the micro-CT technique affords numerous advantages over the conventional approach of parallel dissection followed by image analysis of polished surfaces, and may be useful for determining FLD and FOD in polymer composites with dense matrices.     

Experimental and numerical assessment of mechanical properties of welded tubes for hydroforming

The identification of welded tubes properties considering the weld bead and Heat Affected Zone (HAZ) is important for reliable and accurate finite element simulation of tubular plastic forming processes such as tube hydroforming and rotary draw bending processes. Therefore, a simplified method is proposed to extract the weld bead and HAZ properties. Full size standard tensile specimens cut from the welded tube and comprising the weld parallel to the load direction are extended to failure. Mechanical properties obtained from uniaxial tensile test are correlated with the microhardness data measured across the welded specimen and by using the rule of mixtures; the constitutive model parameters of weld bead and HAZ regions are identified. Accuracy of the proposed method is assessed by comparing finite element simulation predictions to experimental measurements obtained from two mechanical tests: the first one is the uniaxial tensile test performed on specimens comprising the weld line perpendicular to the loading direction and the second test is the free bulge hydroforming test achieved on seamed tubular samples. This investigation has shown that the presented method is practical in use and sufficiently accurate to extract the weld metal properties of seamed tubes.     

Ultimate Strength Prediction of Carbon/Epoxy Tensile Specimens from Acoustic Emission Data

The objective of this paper was to predict the residual strength of post impacted carbon/epoxy composite laminates using an online acoustic emission (AE) monitoring and artificial neural networks (ANN). The laminates were made from eight-layered carbon (in woven mat form) with epoxy as the binding medium by hand lay-up technique and cured at a pressure of 100 kg/cm2 under room temperature using a 30 ton capacity compression molding machine for 24 h. 21 tensile specimens (ASTM D3039 standard) were cut from t...     

A composite index to quantify dispersion of carbon nanotubes in polymer-based composite materials

Several methods with various levels of sophistication exist to quantify dispersion of carbon nanotubes (CNTs) in a polymer matrix, such as the ASTM D2663 standard that is often used in engineering practice. However, most methods are limited by their accuracy, complexity of implementation, and scalability. In this paper, we present a new technique and index to quantify dispersion of CNTs in a composite material. The technique is partially based on a quadrat method, and takes into account the dispersion and agglomerate size distribution of the CNTs. This index is benchmarked against the ASTM index using computer generated images and images experimentally obtained from thirty CNT composite material specimens with different CNT loading rates up to twenty volume percent. The new index is shown to be more versatile and reliable than the ASTM index. It is easily implementable in engineering practice as opposed to other more sophisticated techniques available in the literature.     

Stiffness and energy dissipation in polyurethane auxetic foams

Auxetic open cell polyurethane (PU) foams have been manufactured and mechanically characterised under cyclic tensile loading. The classical manufacturing process for auxetic PU foams involves multiaxial compression of the conventional parent foam, and heating of the compressed specimens above the T_m of the foam polymer. Eighty cylindrical specimens were fabricated using manufacturing routes modified from those in the open literature, with different temperatures (135 °C, 150 °C), compression ratios and different cooling methods (water or room temperature exposure). Compressive tensile cyclic loading has been applied to measure tangent modulus, Poisson’s ratios and energy dissipated per unit volume. The results are used to obtain relations between manufacturing parameters, mechanical and hysteresis properties of the foams. Compression, both radial and axial, was found to be the most significant manufacturing parameter for the auxetic foams in this work.     

Fibre distribution and tensile response anisotropy in sprayed fibre reinforced concrete

Sprayed steel fibre reinforced concrete (SSFRC) is a material that tends to present anisotropy, due to the action of the spraying process inducing preferential fibre orientation. Despite numerous applications worldwide since the 1980s, no study has been found of the assessment of fibre distribution and its influence on the residual tensile strength of SSFRC. This work addresess this issue from a quantitative standpoint through an experimental programme with specimens extracted in various orientations within a SSFRC panel. The fibre content and 3D orientation were quantified using the inductive method and correlated with an indirect tensile behaviour for the same specimen with the Barcelona test. The results confirm the high level of anisotropy of SSFRC. The fibre orientation number parallel to the spraying direction is three times bigger than that found in the perpendicular direction. Similar differences were observed between the residual tensile response measured in those directions. Comparison of test results suggest that the preferential fibre orientation creates weaker planes that favours the increase of crack opening at lower load levels.     

Round robin on creep fatigue crack growth testing for verification of ASTM standard 2760-10

Abstract

This paper presents early results from an ongoing round robin study to verify the newly developed ASTM standard E-2760-10 on creep fatigue crack growth testing. This round robin is an international effort with 18 participants from 11 countries from Asia, North America and Europe. All participants are testing compact type, C(T) specimens according to the procedure described in the standard. The test material is P91 taken from a section of retired steam pipe that was heat treated to rejuvenate the microstructure. All background materials data such as tensile, creep deformation and creep fatigue crack formation data are already available on the test material. Creep fatigue crack growth testing was conducted as part of a pilot program at 625°C using C(T) specimens under constant load amplitude conditions at two load levels. The tests are conducted at hold times of 0, 60 and 600 s. Creep fatigue crack growth rates are analysed using the two methods included as part of the test standard. The data from the various participants will be assessed to determine the expected levels of precision and bias in creep fatigue crack growth data obtained using the ASTM standard. Modifications to the current version of the standard will be proposed and balloted as needed from the round robin results.     

A novel processing technique for thermoplastic manufacturing of unidirectional composites reinforced with jute yarns

This paper primarily investigates the fabrication process of long-fibre reinforced unidirectional thermoplastic composites made using jute yarns (both untreated and treated). Tubular braiding technique was used to produce an intermediate material called “microbraid yarn” (MBY) with jute yarn as the straightly inserted axial reinforcement fibre and polymer matrix fibre being braided around the reinforcing jute yarns. Microbraid yarns were then wound in a parallel configuration onto a metallic frame and compression molded to fabricate unidirectional composite specimens. In this study, two types of polymeric materials (biodegradable poly(lactic) acid and non-biodegradable homo-polypropylene) were used as matrix fibres. Basic static mechanical properties were evaluated from tensile and 3 point bending tests. Test results were analyzed to investigate the effects of molding temperature and pressure on the mechanical and interfacial behaviour. For the unidirectional jute fibre/poly(lactic) acid (PLA) composites, the results indicated that the molding condition at 175 °C and 2.7 MPa pressure was more suitable to obtain optimized properties. Improved wettability due to proper matrix fusion facilitated thorough impregnation, which contributed positively to the fibre/matrix interfacial interactions leading to effective stress transfer from matrix to fibre and improved reinforcing effects of jute yarns. For the jute/PP unidirectional composites, specimens with only 20% of jute fibre content have shown remarkable improvement in tensile and bending properties when compared to those of the virgin PP specimens. The improvements in the mechanical properties are broadly related to various factors, such as the wettability of resin melts into fibre bundles, interfacial adhesion, orientation and uniform distribution of matrix-fibres and the lack of fibre attrition and attenuation during tubular braiding process.