Microstructure-property correlation in martensite-austenite mixtures

The mechanical response of several martensite-austenite mixtures was analysed and related to the existent microstructures. It was found that the mixtures behave as coarse dispersions with deformation taking place by and large in the matrix, austenite. The connectivity of austenite was found to be the crucial factor determining uniform strain.Based upon a dissertation submitted by CBE to the Faculty of IME in partial fulfillment of the requirements for degree of Master of Science.     

Microstructure-property studies in friction-stir welded, Thixomolded magnesium alloy AM60

Thixomolded magnesium alloy AM60 plates joined by friction-stir welding were observed to be as strong or stronger than the unwelded base material. The thixotropic microstructures of the as-molded plates consisted of either 3% or 18% primary solid fraction of -Mg globules (45 m average size) in a eutectic mixture consisting of -Mg grains (10 m) surrounded by Mg₁₇Al₁₂ intermetallic grains in the -Mg grain boundaries (having an average size of 1–2 m). This complex, composite microstructure became a homogeneous (Mg + 6% Al)), recrystallized, equiaxed grain (10–15 m) microstructure in the weld zone.     

Generation of thermal strains in GRP

The temperature dependence of the linear expansion coefficients in the longitudinal (α _l) and transverse directions \((\alpha _{t_1 } and \alpha _{t_2 } )\) of unidirectional glass fibre laminates and their matrix resins (α _m) has been studied. The results for the dry, fully post-cured polyester, epoxy resins and laminates have been found to be consistent with the predictions of the Schapery equations. An anomalous moisture phenomenon, in the form of a peak in theα _m (T)/T andα _t (T)/Tcurves for the polyester resin and laminates has been observed. A difference between \(\alpha _{t_1 }\) and \(\alpha _{t_2 }\) has been observed for partially cured polyester laminates, which is also perturbated in the presence of water. Both these moisture effects, which are not found in the epoxy specimens, are considered to result from a two-phase polyester matrix and the latter to continued curing below the softening point of the resin. These results have a considerable consequence on the magnitude of the thermal strains which develop in polyester composites.     

纤维缠绕玻璃钢管道的渗漏判据

本文通过对无矩层合板细观应变的有限元分析,求得层合板的最大应变集中系数。利用细观力学分析结果,建立了无矩层合板的树脂开裂宏观力学判据。利用该判据建立了管道的渗漏判据。并分析了纤维含量、温差、管径对渗漏压力的影响情况。      

Microstructure-property characterization of a friction-stir welded joint between AA5059 aluminum alloy and high density polyethylene

Aluminum alloys and high density polyethylene are utilized in a wide variety of industrial applications. In the present work the feasibility of friction stir butt welding between AA5059 alloy and high density polyethylene sheets is examined. The bonding mechanism, joint strength, and microhardness are considered in this study. Various welding parameters and tool alignment were investigated until sound joints were achieved by positioning approximately 85% of the rotating tool in the aluminum material on the advancing side (1.4 mm offset) at constant spindle speed and traverse speed of 710 rpm and 63 mm/min, respectively. The results indicate that AA5059 aluminum and high density polyethylene sheets can be successfully joined with a combination of secondary bonding and mechanical interlocking of the materials, which provides a potential alternative to adhesive bonding or mechanical fastening.     

Acoustic emission studies of damage in GRP

A study has been made of the amplitude distributions of acoustic emissions from glass reinforced plastics of several different kinds during tensile loading of test coupons. It is shown that the structure of a GRP laminate exerts a dominating effect on the AE patterns observed, and that direct correlations between microfailure events in the composite and the amplitude distributions of the emissions cannot be made. Understanding of AE patterns from any given GRP material (or structure) may only be possible if there is already a substantial background knowledge of the behaviour of similar materials or structures under known conditions.     

Measurement of surface strains in GRP products

Current work on fibre composite materials required the measurement of surface strains on glass reinforced plastics (GRP) products subjected to static loading. A study undertaken to account for anomalous results obtained with electrical resistance strain gauges showed that strains measured at a given load, increased with decreasing gauge length and foil gauge resistance. Measurement of localised strains using gauges of length up to 25 mm are subject to considerable discrepancy when compared with gauge lengths of less than 13 mm.     

Lateral buckling of pultruded GRP I-section cantilevers

A series of lateral buckling tests on pultruded GRP I-section cantilever beams is described. Comparisons of the theoretical critical loads, determined from approximate formulae and numerical finite element eigenvalue analysis, with the test results are presented. They reveal that linear buckling analysis does not provide an accurate estimate, for use in design, of the maximum tip load that a GRP cantilever may support. It is concluded that both initial deflections and pre-buckling deformations may need to be accounted for in order to model accurately the response of tip loaded pultruded GRP cantilevers.     

Acoustic emission study of impact-damaged GRP pipes

Acoustic emission monitoring techniques have been used to investigate the effects of external damage on the structural integrity of GRP pipes. The pipes were 100 mm bore and 5.5 mm wall thickness, and were of wrapped chopped strand mat glass/polyester construction. Damage caused by severe impacts, of net energies up to 43 J, exerted a marked influence on the observed acoustic emissions from pipes subsequently pressurized to failure, but even though severe microstructural damage was caused by these impacts, they did not reduce the load-bearing capacity of the pipes in any way. The presence of stress concentrators in the form of axial saw-cuts resulted in a changing response to loading roughly in accordance with fracture mechanics predictions, and the results help to explain to some extent the apparently conflicting conclusions from the impact damage studies. Thus, although AE analysis was, for these materials, able to provide a clear indication of the presence of microstructural damage, it is clear that such indications can only be of value in detecting loss of structural integrity (load-bearing ability) when considered in conjunction with other information about the materials involved. Filament-wound pipes, for example, do not behave in the same manner. Amplitude analysis of the AE signals does not appear to be of significant value in giving indications of the nature of the impact damage.     

Extended time tests on GRP pipe bends

Strain measurements were taken on two glass reinforced plastic (GRP) pipe bend specimens made by hand lay-up from polyester resin and E glass in the form of chopped strand mat. Each specimen consisted of a right angled pipe bend with straight lengths at either end. One end was clamped and the free end loaded to give in-plane flexure of the bend. One specimen was subjected to constant load conditions and the other to constant free end displacement over periods up to 329 hours, during which strains were monitored. Finally both specimens were subjected to continuously increasing load up to fracture. During the constant load test there was a little redistribution of strain, but for the constant displacement test there was considerable relaxation of outside surface strains but little change in the corresponding inside surface strains. Results are compared with those for GRP strip tests under three point bending.     

Fracture toughness and crack-growth measurements in GRP

Critical crack tip stress intensity factor (K _c) measurements were made for polyester resin reinforced with glass chopped strand mat (CSM) and woven roving fabric (WRF). Specimen thickness and initial crack length were varied for centre notched (CN) 100 mm wide specimens. Some specimens were saturated by immersion in water under pressure. K _c was negligibly affected by specimen thickness and it was concluded that plane strain conditions are not achieved in laminates of normal thickness. Scatter can be reduced by adjusting results to a standard glass content and K _c varies continuously with crack length. The CSM experiments were extended to 915 mm wide specimens which failed at very low nett section stresses but there may be a region in which K _c is roughly constant relative to crack length. In WRF specimens, however, it is the nett section stress which is constant at a value substantially below the UTS. Fatigue crack-growth studies were carried out on CN specimens. The Paris law adequately describes crack growth in CSM specimens at low rates of growth but Forman's law is better at high rates of growth. Neither law is valid for WRF material when dry but the behaviour changes after saturation with water. The crack-growth resistance of both materials is severely reduced by saturation with water.     

Thermoelastic Stress Analysis of a GRP Tee Joint

A detailed study of the stresses that are developed in a glass reinforced plastic (GRP) tee joint under service loads is described. The joints are fabricated by laminating a boundary angle over a radiused fillet on either side of the ‘tee’. Full-field stress characterisation data is provided by a thermoelastic analysis of the tee joint. Calibration procedures that allow the thermoelastic data to be compared with the results of a finite element analysis are detailed. The results of the thermoelastic analysis are compared with values obtained from the finite element analysis. The applicability of thermoelastic analysis as a validation tool for finite element models of composite materials is assessed.     

GRP管连续缠绕工艺几个问题的研讨

连续缠绕GRP管工艺和设备设计所涉及的技术问题是多方面的。本文着重对“步进式”芯轴实现自动脱模的可行性,芯轴加热以及温度参数调整等方面的问题加以讨论。通过受力分析,导出了自动脱模的条件式的影响脱模的主要因素,此外,给出了芯轴内加热时其表面温度的合理分布曲线以及成型GRP/PVC复合管时采用芯轴内冷却的工艺方案。分析和实验所得出的结论,对于连续缠绕GRP管工艺和设备设计具有一定的参考意义。     

Use of GRP industrial by-products in cement based composites

The possibility of re-using Glass Reinforced Plastic (GRP) industrial by-product powder in cement based composites was investigated. Firstly, the by-product was physically and chemically characterized. Secondly, mechanical, capillary water absorption and shrinkage measurements were carried out on cement mortars manufactured by replacing the 0%, 10%, 15% and 20% of the aggregate volume with GRP by-product and on self compacting concretes manufactured by replacing the 0%, 25% and 50% of the calcareous filler volume with GRP powder. The obtained results show that GRP industrial by-product powder could be used as a partial aggregate or filler replacement in cement based composites. A decrease in mechanical strength was detected on the cement-based materials manufactured by GRP addition. However, capillary water absorption and drying shrinkage of cement-based materials with GRP addition resulted in significantly lower values than those of the cement-based materials manufactured without GRP addition, involving enhanced durability.     

Strength of filament wound GRP pipes with surface crack

In this work, the effect of surface cracks on strength has been investigated theoretically and experimentally for glass/epoxy filament wound pipes, which are mainly used for bazooka launchers. The pipes with surface crack which have several notch-aspect ratios a/c and notch-to-thickness ratios a/t in the axial direction were exposed to open-ended internal pressure. Critical stress intensity factors were determined experimentally for several winding angles by tensile tests with center notched ring specimens. The strength values of pipes with surface cracks are compared with internal pressure test results and theoretical results.     

Through thickness stress distributions in pultruded GRP materials

This paper describes an experimental methodology for determining the through thickness properties of pultruded GRP materials and their application in finite element analysis (FEA) of adhesively bonded joints. The finite element analysis is validated using an infra-red thermography based experimental mechanics technique known as thermoelastic stress analysis. The obtained results show that the measured through thickness values fall within the assumed bounds of previous work and have highlighted that interactions between the fibres and resin in the through thickness direction are present but not in a particularly intuitive manner. Moreover, the work presented herein highlights that the value of shear modulus used in the numerical model is an important consideration.     

Flexure of pultruded GRP beams with semi-rigid end connections

Details of a series of three point flexure tests on 101.6 × 101.6 × 6.4 mm Wide Flange (WF)-section, pultruded Glass Reinforced Plastic (GRP) beams are presented. The beams were tested at four spans (L/d=21–45) under four sets of end conditions: clamped, bolted web and flange cleats, bolted web cleats and simply supported. Mid-span deflections and beam end rotations were recorded in the tests. The observed deflections and end rotations are compared with semi-rigid shear deformable beam theory predictions. Reasons are given for the differences (not large in the majority of cases) between the observed deflections and end rotations and the theoretical predictions. It is shown that deflection reduction and load enhancement performance indices provide a better basis for comparison of the experimental results and the theoretical predictions. The comparisons demonstrate and quantify the improvements in structural performance, arising from the inherent rotational stiffness of practical end connections, which could be utilised at no extra cost by adopting a semi-rigid design philosophy.