Showing papers by "National Aerospace Laboratories published in 1997"

Solid state synthesis and thermal stability of HAP and HAP - beta-TCP composite ceramic powders.

Abstract: Powders of pure β-tricalcium phosphate (β-TCP), hydroxyapatite (HAP) and a biphasic composite mixture of HAP+β-TCP were prepared by solid state reaction between two commercially available calcium-based precursors namely, tricalcium phosphate (TCP) and calcium hydroxide (Ca(OH)2). These reactants mixed in the molar ratios ranging from 3 : 0 to 3 : 4 (designated T0 to T4) in deionized water, milled and slip-cast into discs were heat treated in the temperature range of 600°C to 1250°C. The products formed were characterized by X-ray diffraction (XRD) and i.r. spectroscopic techniques for identification of phases formed and functional groups present in them. While tricalcium phosphate and calcium hydroxide taken in the molar ratio of 3 : 2 and 3 : 3 resulted in pure HAP when heat treated at 1000°C for 8 h, the 3 : 1 and 3 : 1.5 molar ratio compositions resulted in a biphasic mixture of HAP+β-TCP for similar heat treatments. Heat treatment of 3 : 4 molar ratio composition of tricalcium phosphate and calcium hydroxide at 1000°C yielded HAP with free CaO as the secondary phase. Products of heat treatment at higher temperatures (1150 and 1250°C) for even shorter duration (2 h) while not differing from the products obtained from T0 and T2 cases at 1000°C (pure β-TCP and pure HAP), change in the case of T1, T1.5, T3 and T4 to products with lesser percentages of HAP containing β-TCP (in the case of T1 and T1.5) or CaO (in the case of T3 and T4) as the secondary phase.

Scramjet engine test at the Mach 6 flight condition

Abstract: The main purposes of this study are to investigate the effect of strut configurations and isolator length within the engine on the engine performance at Mach 6 condition, and to determine performance of the engine by gas sampling at the exit plane. The sub-scale scramjet engine had an overall length of 2100 mm, height of 250 mm and width of 200 mm and was tested at the Ramjet engine Test Facility (RJTF) of the Kakuda Research Center. In the tests were compared the effects of three strut configurations in an engine with a 200 mm-long isolator on the engine performance. The thrust was measured along with fuel flow rate, and the fuel distribution at the engine exit plane was measured by means of gas sampling. It was found that the strut configuration had an effect on the thrust performance, that the 200 mm-long isolator was effective in preventing combustor/inlet interaction in the engine with the full-height strut, and that the fuel distribution in the engine was not uniform which affected the thrust performance. The maximum thrust obtained was 1620 N at the fuel flow rate of 70 g/s (the bulk equivalence ratio of 0.4).

Three-dimensional eddy structure in a cylindrical container

Abstract: We consider Stokes flow in a cylindrical container of circular section induced by the uniform translatory motion of one of the endwalls. This flow field is of interest because it is possible to get reliable analytical descriptions of important three-dimensional structures such as the primary and corner eddies. It is shown, using a result of TranCong and Blake, that separable solutions exist which can be combined to yield vector eigenfunctions that satisfy the sidewall boundary conditions provided the eigenvalues satisfy the transcendental equation 2kJ. The eigenstructure in the complex plane is somewhat unusual because the eigenvalues form two distinct sequenes: a real-sequence and a complex both of which need to be used to satisfy the top and bottom boundary conditions. The complex eigenvlue with the smallest real part, approximately 2.568+1.123i, determines the spacing and decay of the intensity of the primary eddies in deep containers. The above vector eigenfunctions are first combined, using a least-squares procedure, to determine the flow field in a container of infinite height. It is found, as in the corresponding two-dimensional case, that there is an infinite number of almost equally spaced counter-rotating primary eddies spaced about 2.8 container radii apart. For containers of finite height the number of primary eddies depends on the height of the container; computations show that for container heights of 1 and 2 (based on the radius) there is a single primary eddy while there are two and four respectively for heights of 4 and 10. More interestingly, the corner eddies in the plane of symmetry, rather than being made up of closed streamlines, consist of streamlines that connect the fwo foci at opposite corners in the plane of symmetry. Detailed three-dimensional streamline plots show that away from this plane the flow is almost entirely azimuthal in the corner, a result that would not be evident from two-dimensional results. Other interesting three-dimensional features of the eddy structure are also found. Finally, the growth and merger of the corner eddy as the container height h is increased beyong 3 is studied carefully. Among a number of interesting features, it is found that at some stage streamlines cease to flow into the focus in the centreplane and start, rather, to stream out, resulting on opposite sides of the eddy in the symmetry plane, with local flow from one focus to the other, takes place before the eddy is fully developed. Full merger then takes place when following which the merged eddy gives way to the second primary eddy. We find the corner eddy structure to be quite complicated during the merger process; three-dimensional streamline plots show intricate and rather beautiful patterns in the flow field

FGM research programs in japan —from structural to functional uses

Abstract: The FGM concept can be applied to various material fields for structural and functional uses. In Japan, several five-year programs have been conducted over the past ten years in order to develop the architecture of FGMs, and also to develop these materials for high temperature applications (e.g., components for the hypersonic space plane) and for functional applications (e.g., thermoelectric and thermionic converters). These programs are discussed with respect to the construction of FGM architecture and the future of FGMs.

Straightforward inversion of vertical electrical sounding data

Abstract: A straightforward inversion scheme (SIS) has been developed to interpret vertical electrical sounding data. This scheme does not require quasi-linearization of the inverse resistivity problem and thereby dispenses with the iterative process and the necessity of guessing the number of layers and their resistivities and thicknesses. The entire solution domain is divided into uniform thickness layers, whose scale must be judiciously selected for the desired resolution. The apparent resistivity formula can now be posed as an underdetermined matrix equation whose minimum norm solution is downward continued to obtain the reflection coefficients which, in turn, yield the vertical resistivity distribution. A recurrence relation has been developed especially for this purpose. In general, when data are expected to be noisy, a regressed minimum norm solution is used. Exhaustive tests of the algorithm have established its numerical efficiency. Results of six typical synthetic models, representing diverse geological conditions, as well as results of two field examples are included to demonstrate this claim.

Comparative Study of Recessed and Non-recessed Swirl Coaxial Injectors

Abstract: The combustion characteristics of swirl-coaxial injectors with LOX/hydrogen were experimentally evaluated. Cold flow tests with water/nitrogen gas showed the known self-pulsating flow with swirl-coaxial injectors with recessed LOX post Combustion tests with single element combustors were conducted at chamber pressures of 2.6 MPa and 3.5 MPa, thrusts of 850 N and 500 N, and an oxidant to fuel ratio of 4.0 to 8.0. Combustion performance, chamber pressure distribution, and heat load on the chamber wall for each injector were measured and analyzed. The results indicated that the combustion performance was mainly limited by the vaporization efficiency in the shear-coaxial injector and by the mixing efficiency in the swirl-coaxial injectors. A significant increase of heat load on the chamber wall was observed with recessed swirl-coaxial injectors, and in some cases, the occurrence of unstable combustion was also observed.

Transonic Wing Optimization Using Genetic Algorithm

Abstract: A Genetic Algorithm (GA) has been applied to optimize a transonic wing shape for generic transport aircraft. A threedimensional compressible Navier-Stokes (N-S) solver is used to evaluate aerodynamic performance. The N-S evaluation is parallelized on Numerical Wind Tunnel (NWT) at National Aerospace Laboratory in Japan, a parallel vector machine with 166 processing elements. Designed wings show a tradeoff between an increase of the airfoil thickness driven by a structural constraint and a reduction of the wave drag produced by a shock wave. The present result indicates that GA has found a best feasible solution in the given design constraints.

Experimental and analytical estimates of fatigue crack closure in an aluminium‐copper alloy part ii: a finite element analysis

Abstract: A numerical investigation of the fatigue crack closure phenomenon has been performed by an elastic-plastic finite element analysis. Computer software was developed to consider many aspects affecting plasticity-induced crack closure. Linear and power-law hardening models are considered in the finite element analysis. The paper presents results from the study carried out on compact tension (CT) coupons at various crack lengths corresponding to different loading conditions. Finally the results of the analysis are compared with the experimental estimates of fatigue crack closure levels obtained from laser interferometry, scanning-electron and transmission-electron fractography presented in Part I of this paper on identical specimens.

A low-order theory for stability of non-parallel boundary layer flows

Abstract: As a sequel to the earlier analysis of Govindarajan and Narasimha, we formulate here the lowest‐order rational asymptotic theory capable of handling the linear stability of spatially developing two‐dimensional boundary layers. It is shown that a new ordinary differential equation, using similarity‐transformed variables in Falkner–Skan flows, provides such a theory correct upto (but not including) O ( R −2/3), where R is the local boundary layer thickness Reynolds number. The equation so derived differs from the Orr–Sommerfeld in two respects: the terms representing streamwise diffusion of vorticity are absent; but a new term for the advection of disturbance vorticity at the critical layer by the mean wall‐normal velocity was found necessary. Results from the present lowest‐order theory show reasonable agreement with the full O ( R −1) theory. Stability loops at different wall‐normal distances, in either theory, show certain peculiar characteristics that have not been reported so far but are demonstrated here to be necessary consequences of flow non‐parallelism.

Generation of Comprehensive Longitudinal Aerodynamic Data Using Dynamic Wind-Tunnel Simulation

Abstract: A novel method of generating comprehensive longitudinal aerodynamic data of aircraft using dynamic wind-tunnel simulation is presented. The method utilizes the motion and force responses of an aircraft model to control surface inputs to determine trim lift characteristics, longitudinal stability derivatives, and neutral point. In addition, large-amplitude lift and pitching moment responses characterizing the unsteady aerodynamic behavior are also generated using the same experimental setup. The new test method is demonstrated using a generic delta wing aircraft model with one degree of freedom in pitch. The model pitch attitude and lift force responses to elevon dynamic inputs are measured and used to deduce longitudinal aerodynamic data. Comparison of these results with static test data and Datcom estimates shows good agreement. Nomenclature CL = lift coefe cient, L/qS CLa = lift curve slope, rad 21

Measurement of blade tip clearance using an ultrasonic sensor

Abstract: This paper describes a development and evaluation of a blade tip clearance measurement system using an ultrasonic sensor. Special features of this system are; (i) it is adequate for metal and non-metal blade; (ii) it permits measurement without contact; (iii) it can work in dirty environment; and (iv) it is easy to install. Experimental results using a rotating blade test rig are described. Blade tip speed is restricted to Mach 0.18 due to the limitation of the test rig. It is concluded that the ultrasonic method is a promising candidate for an on-line clearance control of gas turbine engines.

Preparation of pure boehmite, α--Al2O3 and their mixtures by hydrothermal oxidation of aluminium metal

Abstract: A hydrothermal oxidation process for preparing pure boehmite, alpha-Al2O3, and their mixtures by oxidation of pure aluminum metal is described, and the reaction mechanisms involved are identified SEM images are presented which show distinct morphologies of boehmite, alpha-Al2O3, and boehmite + alpha-Al2O3 phases Near sperical shapes of alpha-Al2O3 powder phases are obtained at 550 C with 30 percent volume of fill

Cu as an additive in the As0.4Se0.2Te0.4 glass: mean atomic volume and Tg

Abstract: Data on the mean atomic volume (V) and the glass transition temperature (Tg) of the As0.4Se0.3Te0.3 glass, modified with Cu are reported and discussed. The V and Tg of the parent glass are invariant with addition of ≤1 atomic percent (at.%) of Cu up to which clusters of Cu atoms occupy interlayer positions in the layered network of the parent glass. For additions of Cu>1 at.%, a decrease in V and an increase in Tg are observed. The composition dependencies of V and Tg are consistent with a model according to which, with progressive increase in the Cu content, some of the original As2Se3 and As2Te3 structural units of the parent glass are replaced, respectively, by CuAsSe2 and CuAsTe structural units. For Cu≥23.08 at.%, after the formation of CuAsSe2 structural units, there is no free Se available for the formation of As2Se3 structural units; as no free Se is available, a change of slope occurs in the V–composition and Tg–composition data at the Cu content of 23.08 at.%. The increase in Tg with increasing Cu content is due to an increase in the average coordination number brought about by an increase in cross linking due to the formation of tetrahedral CuAsSe2 and CuAsTe complexes in the glasses.

LOX/LH2 Subscale Swirl Coaxial Injector Testing

Abstract: To obtain design technology necessary for the realization of large swirl coaxial injectors with high performance, multi-element combustors composed of 9-shear-coaxiaI or 9-swirl-coaxial injection elements were tested at a nominal thrust of 10 kN, a chamber pressure of 3.5 MPa, a mixture ratio of 4.5 to 7.5, and a hydrogen injection temperature of 40 to 50 K. Combustion performance, chamber pressure distribution, chamber heat load, and stability data for each injector were obtained and compared with each other with reference to the authors' single element results. Measured data showed a reasonable correspondence and the difference of combustion characteristics between the shear coaxial injector and swirl coaxial injectors was apparent

Acid Resistance of Glass Fibre Composites with Different Layup Sequencing Part II: Degradation Studies:

Abstract: The effects of sulphuric acid,concentration nd the sequential layup of glass fiber reinforcement on the diffusion behavior of glass epoxy composite laminates were studied. In all, composites of six d t f f h n t resin systems viz., general purpose polyester, bis phenol-A polyester, vinyl ester, LY 556 epoxy, and MY 750 epoxy resins, reinforced with differen1 layup sequencing consisting of chopped strand mar (CSM) and woven roving mat (WR) were exposed to ,sulphuric acid environments of different concentrations. The results of the study indicated that isophrhalic polyester resin exhibited maximum resistance to sulphuric acid while general purpose polyester resin performed relatively inferior. The diffusion phenomenon became anamalous as the concentration of the sulphuric acid increased. Among the layup sequences considered, composite specimens with CSM as the skin layers exhibited higher weight gain than those with WR as the skin layer;.

Auto ignit-ion in a supersonic combustor with perpendicular injection behind backward-facing step

Abstract: Flow field at pre-ignition phase in a supersonic combustor with perpendicular injections behind a backward facing step was simulated in cold flow tests with inert gas injection, to investigate the mechanism of the ignition enhancement observed in the ignition tests with the same combustor. The interaction, namely the merging, of separation at step base with that upstream of the injector caused enlargement of ignition region and the enhancement. The change in ignition ability was estimated based on ignition parameters. Based on the experimentally obtained ignition parameters, the ignition limit for the interacted separation region was predicted and showed reasonable agreement with the experimental results.

Experimental and analytical estimates of fatigue crack closure in an aluminium-copper alloy. Part I: Laser interferometry and electron fractography

Abstract: Results of an experimental estimation of the crack closure stress, using electron fractography and laser interferometry for CT specimens of an aluminium-copper alloy are presented in this paper. Crack closure stress was estimated at stress ratios of 0.1, 0.3, 0.5 and 0.7 using programmed load sequences. In addition, the crack closure stress was estimated for a simple random load sequence. Scanning and transmission electron fractography provided a similar estimate of crack closure, with the later technique providing better quality fractographs. Laser-interferometry based estimates were closer to fractographic estimates when the crack-tip is very close to the micro-indent axis. In addition, laser-interferometry based estimates of the crack opening stress for a random load sequence, confirmed the possibility of a cycle-by-cycle variation of the crack opening stress.

Application of an AOTF imaging spectropolarimeter

Abstract: An imaging radiometer is one of the most fundamental optics sensors for aircraft as well as satellite remote sensing The important points on the future imaging radiometers are hyper-spectral resolution, wavelength running capability, and polarimetry would give us further information The basic problem is the requirement for two simultaneous photometric measurements of every point in the sensor field of view for the two orthogonal polarization components Then we developed a tunable spectral and polarimetric radiometer: an AOTF imaging spectro-polarization components Then we developed a tunable spectral and polarimetric radiometer: an AOTF imaging spectro-polarimeter which uses an acousto-optic tunable filter (AOTF) as spectroscopic as well as polarimetric element The specific point of the device is that we can simultaneously obtain two diffracted beams and images perpendicularly polarized to each other The instrument employs an reviewing the concept, configuration and performance of the instrument, applications of the instrument will be presented: the laboratory measurements of light scattering by rough surfaces, the aerosol measurements from the ground, and more

Geometrical effects to aerodynamic performance of scramjet engine

Abstract: A side wall compression type scramjet model was tested at Mach 4, 6 and 8 flight conditions. The effects of the incoming Mach number on the aerodynamic performance were investigated with a simple model, and it was found that the compression ratio was not high enough in M6 and M8 cases. Additional structures like a strut were applied to the model to enhance the pressure ratio. The results showed that it would achieve higher pressure in some regions, but always associated with the local pressure decrease. The aerodynamic coefficients study of every configuration tested here showed the modifications with these structures would increase the drag coefficient by the factor of up to 1.3. The modification should be made with a proper configuration , at proper location, considering with the combustion requirement.

Rotating Cavitation in Three and Four-Bladed Inducers

Abstract: Recently, rotating cavitation occurred in the inducers of propellant feed pumps during the development of large advanced rocket engines, such as the LE-7, Ariane 5, and the Space Shuttle Main Engine. With regard to suction and overall performance, some comparisons have been made as to the numbers of blades. For example, it was reported that good suction performance was obtained with a small number of blades and that a three-bladed inducer is preferable if design considerations permit. Furthermore, it is well known that alternate blade cavitation occurs in the four-bladed inducer. However, it was recently clarified that attached cavitation or steady asymmetric cavitation occurs in the three-bladed inducer. Attached cavitation causes radial thrust due to an asymmetric pressure distribution around the periphery of the inducer inlet, while alternate blade cavitation does not cause radial thrust due to symmetric pressure distribution. We performed further experiments to investigate the difference of rotating and attached (or alternate blade) cavitation between three- and four-bladed inducers which had almost the same dimensions.

RCS gas-jet interaction in the Hypersonic Flight Experiment, HYFLEX

Abstract: The RCS gas-jet interaction experiment in the Hypersonic Flight Experiment, HYFLEX, was performed for the purpose of evaluating a method to estimate the jet interaction effects in flight condition, based on wind tunnel tests and/or CFD calculations. In this paper, flight data on surface pressure distribution measurement around a RCS thruster are presented in supersonic to hypersonic speed ranges, being compared with several wind tunnel test results and CFD calculations. Three correlation parameters of the jet interaction phenomena ( pressure ratio, mass flow ratio, and momentum ratio ) are examined in the comparisons. The results show that jet momentum ratio to external flow is generally a suitable correlation parameter in the case of the experimental yaw thruster in laminar boundary layer condition. On the other hand, mass flow ratio is estimated to be a better parameter than momentum ratio for turbulent boundary layer condition. NOMENCLATURE A area, m 2 b body width, m Ci rolling moment coefficient, L/qSb Ca yawing moment coefficient, N/qSb Cp pressure coefficient (p-p ~>)/q IB body length, m K jet thrust amplification factor, Eq.(4) L rolling moment, N-m rh mass flow rate, kg/s M Mach number MFR jet mass flow ratio to freestream, Eq.(2) MTR jet momentum ratio to freestream, Eq.(3) N yawing moment, N-m PRR jet static pressure ratio to freestream, Eq.(l) p static pressure, Pa q dynamic pressure, Pa Re Reynolds number based on body length * Senior Researcher, Aerodynamics Division. Member AIAA. t Researcher, Computational Sciences Division. Member AIAA. t Laboratory Head, Aerodynamics Division. Member AIAA. Copyright © 1997 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Re Reynolds number based on body length S vehicle planform area, m 2 T temperature, K; thrust, N V velocity, m/s X,Y,Z coordinates fixed to vehicle, m (see Fig.l) a angle of attack, deg A increment due to jet interaction y specific heat ratio Subscripts: 0 stagnation condition CG vehicle center of gravity VAC vacuum condition j condition of jet at nozzle exit °° freestream condition INTRODUCTION HYFLEX Hypersonic Flight Experiment was planned as the first Japanese lifting hypersonic flight in order to acquire flight data needed for the development of the Japanese operational unmanned orbiting plane, HOPE ' . The HYFLEX flight was successfully conducted on Feb. 12, 1996, using a small lifting body-type vehicle 2 . After the vehicle was accelerated by a two-stage solid rocket motor and separated at an altitude of 107 km with a velocity of 3.9 km/s, the vehicle glided down with guidance and control. Flight data acquired in HYFLEX consist of data on hypersonic aerodynamics, thermal protection system, and guidance and control. As an important item of the measurements on aerodynamics , RCS gas-jet interaction measurement was performed because estimation of aerodynamic interaction effects between RCS gas-jet and external flow have been one of key technologies in hypersonic reentry vehicle development. The experiment was aimed at evaluating a method to estimate the interaction effects in flight condition, based on ground-based data. In this paper, surface pressure distribution data affected by the gas-jet interaction phenomena are presented in comparison with wind tunnel test results simulating several candidates for jet interaction correlation parameter. In order to extract a suitable correlation parameter, the parameters as candidates American Institute of Aeronautics and Astronautics are examined in respect to interaction effects on surface pressure distribution, aerodynamic moment, and net thrust of thruster. CFD calculations are also conducted for validating the Navier-Stokes code used to solve the gas-jet interaction flowfield. REACTION CONTROL SYSTEM (RCS) Attitude of the HYELEX vehicle is controlled by coordinating an aerodynamic control surface called 'eleven' and a three-axis gas-jet reaction control system (RCS) . In low dynamic pressure region just after the vehicle separation, the vehicle is controlled only by the three-axis RCS. After reaching certain dynamic pressure, the control law changes to a combined attitude control by the eleven and the yaw RCS thrusters, continuing down to Mach 2. Figure 1 shows the vehicle configuration and arrangement of the RCS thrusters. Table 1 shows reference values of the vehicle for nondimensionalizing aerodynamic force and moment. The RCS thrusters are divided into two categories with different functions. The first category consists of six thrusters for controlling the vehicle attitude. The thrusters are located on thruster module bulges installed on the vehicle body base area in order to avoid unexpected gas-jet interaction effects on the attitude control. The second one is for investigating aerodynamic interaction phenomena between a RCS gas-jet and an external stream. Two experimental yaw thrusters which are installed in a symmetrical position on rear part of vertical stabilizing fins are used only for the purpose. The jet gas supplied to all of the thrusters is nitrogen without heating. Dimensions and performance of the experimental yaw thrusters are summarized in Table 2. The nozzle has a conical shape with a semi-vertex angle of 20 deg. The expansion ratio of it is equal to 57. The nozzle center axis is parallel to the vehicle Y-axis, so that it is not perpendicular to the outer surface of the stabilizing fin. Theoretical Mach number of the jet flow at the nozzle exit is 6.09. Stagnation pressure in the settling chamber of the nozzle poj is always regulated to a constant pressure. Stagnation temperature TOJ gradually decreases from room temperature with the decrease in nitrogen pressure in an accumulating tank. ONBOARD MEASUREMENT APPARATUS AND PROCEDURE In order to examine the gas-jet interaction effects, surface pressure distribution was measured around the experimental yaw thruster during the flight. As shown in Fig.2, twelve pressure orifices are located only on the left-side stabilizing fin, which have three-row arrangement nearly parallel to the leading edge of the fin. As observed in oil flow tests in hypersonic wind tunnels, the rows are nearly parallel to stream line of the external flow on the fin at angles of attack in the flight. Considering unexpectedly strong jet interaction effects, a wide area around the thruster is covered by the orifices. High accuracy pressure transducers with frequency outputs are used for each of the orifices. After the 20Hz-sampled outputs are sent to a PCM telemeter package through a signal conditioner with A/D converters, the data are transmitted by telemetry to the ground. During the flight, an onboard computer calculates gas-jet mass flow ratio to freestream and flight Mach number based on the estimated velocity and altitude, assuming the US Standard Atmosphere model. When the mass flow ratio or the flight Mach number becomes equal to specified values determined prior to the flight, the experimental thruster injects nitrogen gas for a period of 0.5 sec. Ten injections were planned during the flight. Both of the experimental yaw thrusters on the left and right fins are injected together to cancel yawing moment which may disturb the vehicle altitude control. Therefore, variations of aerodynamic moment due to the jet interactions can not be known directly from the flight data. Figure 3 shows the experimental yaw thruster injection timing in the real flight. In accordance with the test plan, ten injections of jet ( injection #1 to #10 ) were certainly performed from Mach 14 down to 3. The first five injections were conducted at an angle of attack of 49 deg and the remains at an angle of 30 deg. Various correlation parameters have been proposed for the gas-jet interaction phenomena 5 . In the flight data analysis of the Space Shuttle Orbiter, several correlation parameters were extensively compared" . In HYFLEX, three correlation parameters defined in the following equations were examined as candidates for a suitable correlation parameter. PL Pressure ratio Mass flow ratio (1)

Measurement of residual stresses in CFRP laminates by X-ray diffraction method

Abstract: The fabrication of CFRP laminates from prepregs involves curing at elevated temperatures. Residual stresses are set up due to the difference in thermal expansion coefficient between the matrix and the fibre. In this investigation, the X-ray diffraction method is used to measure the curing stresses in CFRP laminates by incorporating a very fine layer of aluminium particles during the lay up of the laminate. A calibration procedure is followed to correlate the strain in the crystalline particles, as measured by X-rays, with the composite strain and stress. Curing stresses measured by this technique are quite close to the value calculated from the differential coefficient of thermal expansion.