Pressureless sintered alumina with 92% purity was quenched from 1500°C into silicon oil with the kinematic viscosity of 1, 100 and 10000cs. The residual stress distribution in the quenched ceramics was measured by the X-ray diffraction method. The increase of the bending strength of quenched ceramics was discussed on the basis of the measured residual stress. The results obtained were summarized as follows: The compressive residual stress was formed near the surface of quenched ceramics, and its magnitude increased with decreasing viscosity of silicon oil. The bending fracture of quenched ceramics started from the material defect embedded in the surface layer with large compressive residual stresses. The bending strength increased in proportion to the amount of compressive residual stress measured on the surface. The maximum strength was obtained for the case of quenching into 1cs silicon oil. It was 531MPa which is about 1.4 times the strength of annealed specimens. The microscopic residual stress, estimated from the broadening of the X-ray diffraction profile, could reduce the stress for fracture from a small (microscopic) defect.
In the previous study, it was found that heat treatments of quenching and tempering after TiC coating improved the fatigue strength, and also the fatigue life of TiC coated steels depended on the hardness of substrate. In this study, the authors investigated in detail the effect of condition of quenching and tempering after TiC coating on the fatigue strength of tool steel. Four kinds of quenching and tempering conditions after TiC coating were selected, but TiC coating condition was all the same. Fatigue tests were conducted using the smooth specimens of a flat plate. The residual stresses were measured by an X-ray diffraction method. As the results, it was found that the condition of heat treatment of quenching and tempering influenced the hardness of substrate and consequently the fatigue strength which was not necessarily dominated by the hardness of substrate, and there existed an optimal hardness of substrate in relation to the fatigue strength. And it was reconfirmed that tensile stress existing in the top part of substrate, which was balanced by the compressive stress in TiC layer, was not only the main factor controlling the fatigue strength, and the secondary tempering condition played some role.
Strain-controlled low cycle fatigue damage has been studied by means of X-ray diffraction and AE (acoustic emission) methods in addition to metallographic technique for the following two types of formable 60kgf/mm2 class hot-rolled high strength sheet steels; a 0.9%Si-1.2%Mn dual phase (DP) hardened steel with duplex microstructures of ferrite and martensite and a 0.04%Nb added precipitation hardened fine grain steel. The following results were obtained. (1) The Nb added steel showed monotonic cyclic softening, causing a decrease in X-ray half value breadth as a result of sub-boundaries due to the rearrangement of dislocation during the repeated cyclic strain. On the other hand, the Si-Mn DP steel showed cyclic hardening at the early stage followed by softening, which corresponds to an increase followed by a slight decrease in X-ray half value breadth caused by fine cell-structures in the ferrite matrix, which were essentially stable even in the cyclic softening stage. (2) The Si-Mn DP steel gave more and smaller AE waves in the early and the middle stages than the Nb added steel. The phenomenon in the DP steel might be the result of the continuous release of elastic energy due to the formation and annihilation of persistent slipbands in the ferrite matrix, and the initiation of small cracks at ferrite/martensite boundaries. The Si-Mn DP steel showed consequently higher registance to the fatal cracking than the other.
In order to predict the crack initiation life at periphery grooves for high-temperature rotors in a fossil power plant, a study using X-ray diffraction was conducted. As a conclusion of the study, a diagram for estimating the fatigue life fraction was presented based on the following findings: (1) The half-value breadth of X-ray diffraction line generally decreased with an increase in fatigue damage for Cr-Mo-V material at service temperature of about 500°C. (2) For the constant strain cycling, it was possible to express the relation between the change in half-value breadth and the logarithm of cyclic number by a straight line except in the early part of life. The slope of the line seemed to take a constant value regardless, the strain range. On the other hand, the relation between the half-value breadth and the number of cycles to crack initiation was abe to be expressed using a straight line on the semi-log plotting. (3) Based on the result of (2), it is possible to propose a method for estimating the fatigue life fraction for constant strain cycling. (4) It was recognized that the method is also valid for estimating the fatigue life fraction for two-step multiple strain cycling and strain cycling with hold time.
Failures in operation sometimes result from defects in engineering structures. The purpose of failure analysis is to determine the cause of failure. In order to prevent the failure accidents, it is necessary to make a quantitative analysis on the fracture surface. In the present paper the X-ray fractographic technique was applied to the examples of actual fracture of machine parts. The distribution of the residual stress beneath the fracture surface was measured with the X-ray diffraction technique. The plastic zone size was determined from the distribution of the residual stress and was used to estimate the actual fracture stress.
It is difficult to approximate a diffraction profile to Gaussian curves precisely by using a method of linear least squares. Therefore, a method to approximate it to multiple Gaussian curves by using a method of nonlinear least squares was developed. The present analytical method can be applied widely because it has the following advanteges. 1) A whole diffraction profile can be approximated with high accuracy. 2) The peek position, half value breadth of a diffraction profile, maximum intensity and background intensity can be obtained simultaneously. 3) The measurement system can store the profiles in the form of coefficients of diffraction profiles easily and reproduce them when needed. 4) Multiple diffraction curves can be separated easily. 5) The method makes it possible to separate an unnecessary diffraction profile from the necessary ones and then eliminate it. 6) When this method is utilized, an appropriate initial value of each parameter is necessary. The value decided by a method of linear least squares can be used as the initial value.
When stress gradient exists in the irradiated area of X-ray diffraction measurement on the surface of a specimen, the half value breadth of diffraction profile (Hw) increases in comparison with that without stress gradient (Hw0). When the stress distribution in the irradiated area is uniaxially linear, the change of stress in the irradiated area is proportional to the difference of diffraction angle or peak shift in the area because the diffraction angle at each position in the irradiated area changes linearly. Furthermore, the half value breadth of the profile with stress distribution must be related to the peak shift because the diffraction profile with stress distribution is measured as the integrated sum of the profile at each position in the irradiated area. In the present study, the quantitative relation between the half value breadth ratio Hw/Hw0 and the peak shift of profile in the irradiated area was analyzed numerically and experimentally. And a technique to measure simultaneously the stress gradient by using the half value breadth ratio and the X-ray stress was proposed. Cyclic stress was applied on a thin steel specimen, and the X-ray stress and stress rate as dynamic stress gradient were measured as the mean values during a time interval for the measurement of diffraction profile. And it was verified that the measurement of stress gradient with high accuracy required the incident angle of X-ray beam as large as possible and the error of stress gradient increased with decreasing change of stress in the irradiated area.
The development of ceramic coating to metals was stimulated by the need for high temperature, wear and corrosion resistant materials. Recently TiC is used as a ceramic coating material. In the present study, the X-ray method was successfully applied to measure the residual stress distribution in TiC coated steels. The X-ray elastic constants were determined and compared with the mechanically measured values. The results obtained are summarized as follows; (1) The X-ray elastic constants determined were As-coated: S1=3.97×10-4(GPa-1), S2/2=2.92×10-3(GPa-1) Quenched: S2/2=1.89×10-3(GPa-1) Annealed: S2/2=2.07×10-3(GPa-1) Quenched and Tempered: S2/2=1.13×10-3(GPa-1) for TiC (113) phase. And As-coated Ex-ray was 397(GPa) which was lower than the mechanically determined value of 421(GPa), respectively. (2) The residual stress distribution determined by the X-ray method indicated high compressive stress above -1.5--3.5(GPa) in the TiC layer.
When long steel sheet-piles are driven into sandy soil, their grips occasionally separate. A clear explanation has not been obtained regarding this phenomenon because it occurs in the soil. One of the purposes of this study was to clarify the deformation mechanism of the steel sheet-pile grip and to find out the factors affecting grip separation. Another purpose was to develop a sheet pile with a grip that does not easily separate during construction. In this paper, the sand pressure occuring in the grip was assumed to be replaced by equivalent external force, so that the deformation of the grip by external force could be observed. This experiment showed that the separation limit of the steel sheet-pile grip is controlled by the dimension and strength of the root of the steel sheet-pile finger. The sand pressure at grip separation estimated by this experiment was the same as that estimated by the repetition of pile driving in the sand pit in the laboratory. From these experiments, a steel sheet-pile, which is strongly resistive to grip separation, was discovered. This steel sheet-pile can be easily produced by rolling.
Elasto-plastic deformation and fracture strength of single lap joints were investigated experimentally and analytically. The joint adherends were carbon steel and aluminum alloy. The adhesive was epoxy resin. The stress and strain in the joints under tensile loading were analyzed by using elasto-plastic finite element method. The variation of plastic region in the joints was examined with increasing applied load. The stress and strain curves in the adherends were compared with the experimental results. The fracture strength of breaking the joints was examined based on the stress and strain conditions in the adhesive layer and adherends near the adhesive interfaces.
This study was conducted to estimate the rigidity and the deformation of the fiber composites with complicated fiber orientation. The new method which was able to indicate various fiber oriented states by use of an incomplete beta function was proposed in the previous paper. In this paper, a generalized laminated theory was presented to analyse the stress-strain relation for the fiber composites with a certain fiber oriented distribution. The effect of fiber oriented distribution on the elastic moduli of these composites was discussed by the proposed formulation. The numerical results on the elastic moduli agreed well with the experimental data. Furthermore, the deformation behavior of a laminated plate was estimated by combining this lamination theory with the finite element method. The numerical example of the deformation under uniaxial loading was shown for a composite plate with a typical orientation state.
A relation between creep rate versus time is more characteristic of creep deformation behaviour than a relation between creep strain versus time, that is, a creep curve. The relation between creep rate versus time normarized by time to rupture was examined for 2.25Cr-1Mo, SUS 304 and 316 steels in order to clarify the dependences of materials and testing conditions on the creep deformation behaviour. It was found that the creep deformation behaviour was classified into four types. These four types of creep deformation behaviour were distinctly dependent on temperature and stress conditions, so a creep deformation type map was constructed for each steel. The simple expression of creep strain for each creep deformation type was proposed, and the appropriateness of these expressions was verified.
The biaxial creep deformation of a thin-walled tube of celluloid softened by heating was tested under variable torsional stress consisting of stepwise increase, removal and reversal with superimposed constant axial stress. The results are summarized as follows. (1) The axial creep strain is affected by the reversal of torsional stress under constant axial stress. The axial creep strain rate increases just after the reversal of torsional stress. Although axial creep strain increases in the resting stage of torsional stress, the increment of the strain is smaller than that in the loading stage under torsional stress. (2) There appears the softening of torsional creep strain at the first reversal of torsional stress. The amount of variation of torsional creep strain decreases with the number of torsional stress reversal. The amount of recoverable torsional creep strain depends not on axial stress but on torsional stress, and the variation of the recoverable strain decreases with the number of stages. (3) Just after the abrupt change of stress vector, the direction of creep strain increment vector inclines to show the direction of torsional stress from that of stress vector. The directions of creep strain increment vector and stress vector coincides with each other with the lapse of time. (4) In the resting stage, the angle between creep strain increment vector and stress vector is large and the length of creep strain path is short. In the loading stage under torsional stress, the angle is smaller than that in the resting stage, and the length of creep strain path is long.
Crack propagation and branching behavior in a disk under axisymmetrical tension was analyzed by using an energy consideration. The result was compared with the experimental result of flexual test in which a glass or ceramic disk was supported along its edge and load was applied at the center of disk. If crack branching occurs by the decrease of free energy of the system, the crack length ai after the i-th crack branching has occurred is given as follows: ai≈22i+1/(2i+1-1)·Eγ/πσ2 Where E is elastic modulus, γ is surface energy, σ is tensile stress, and n=2i+1 is number of cracks. The surface energy γ, which was calculated by dividing the stored strain energy in a disk before fracture by the total crack surface, was almost the same independently of the number of cracks. The crack branching pattern observed for disk specimens agreed relatively well with the pattern calculated from the above equation.
It is difficult to conduct cyclic tensile fatigue tests for fine ceramics because of its high brittleness, and a little eccentricity of loading axis and gripping device gives inaccurate strength data. So, a major part of cyclic fatigue tests have been carried out under bending load conditions, for the allowance of misalignment of loading axis is generous to some extent in the case of bending fatigue. As is well known, fatigue strength together with other fracture strength is critically affected by pre-existing defects, and consequently, the distribution of fatigue lives is very large even at high stress levels depending on the distribution characteristics of the defects. To evaluate precisely the correlation between the distribution features of the defects and lives, it is preferable to discuss the contribution of the defects and their distribution to the fatigue strength on the basis of the fatigue strength data under tensile load condition to exclude the influence of stress gradient in the specimen. In this paper, the results of static and cyclic fatigue tests under tensile and 3-point bending load conditions are discussed, where self-aligning rings for loading axis developed by the authors are equipped to the gripping devices in the case of tensile fatigue tests. The fatigue data obtained in this study are evaluated with the initial stress intensity factor for pre-existing defects at the fracture origination site, and the effect of stress pattern on fatigue strength is discussed from several points of view.
In this paper, a fatigue life prediction method based on linear fracture mechanics is proposed to composite materials. In order to evaluate this method, the cyclic loading tests of graphite/epoxy composites plates with [±30]s, [±45]s and [±60]s laminate orientations were carried out. It was revealed that the computational result was satisfactory agreement with the experimental ones except long life region [±30]s laminate orientations. The fracture mode was the combination of tension and shear modes when the angle between loading direction and fiber orientation became small. Therefore, it is recognized that the long life prediction of these materials has to require fracture mechanics base on the combined mode which is not dealt with in this paper. Furthermore, the effects of material properties on fatigue life were investigated as an application of the proposed model to material design. As a result, it became clear that the fatigue life is affected by the ultimate tensile and shear strengths of the matrix and depends strongly on the influence of initial crack length that is calculated from the size of voids or defects.
The influence of environmental temperature on fatigue property of center hole notched GFRP reinforced by plain woven glass cloth was studied. In this paper, first, the fracture surface of GFRP after fatigue failure was observed by SEM photograph, and the difference of microscopic fracture style caused by the difference of environmental temperature was investigated. The matrix crack density produced in the fatigue process was measured, and the relation between crack density and modulus decay was confirmed. Then, the static and fatigue notch factors defined as the ratio of strength of the unnotched specimen to that of the hole notched specimen at a certain number of cycles were measured at various test temperatures. The temperature dependence of macroscopic fatigue process for the hole notched specimens with different hole diameters was considered. As the result, the following conclusions were obtained. When the environmental temperature rose, the microscopic fracture style shifted to the interface fracture from the cohesive fracture. Lower the environmental temperature, lower the stiffness modulus of the unnotched specimen under the fatigue process. Especially it was remarkable in the middle stage of the fatigue process, because the matrix is brittle and many matrix cracks are produced at low temperatures. For the hole notched specimen, the notch factor decreased with an increase of number of loading cycles for the whole range of hole diameter, because the stress concentration is relaxed by local modulus decay. However, at a low temperature and for small notched diameter, the fatigue notch factor increased with number of cycles, because of brittleness of matrix and remarkable propagation of matrix cracks from the vicinity of hole to its periphery. At high temperatures, it also increased because stress relaxation with local modulus decay does not progress so much comparatively.
Fracture strength and fracture toughness tests were carried out on HIP-sintered TiB2 specimens at elevated temperatures and the mechanisms of strengthening and toughening by oxidation at elevated temperatures were investigated. Both the fracture strength and fracture toughness of TiB2 increased with increasing temperature up to 800-1100K and then decreased. The room-temperature strength of the specimens heated at elevated temperatures showed a similar temperature dependence of high-temperature strength. The mechanism of strengthening of the oxidized TiB2 seems to be as follows. When the TiB2 specimen is heated, the volumetric expansion due to the oxidation reaction of TiC→TiO2, where TiC is used as a sintering additive, occurs. This volumetric expansion near the surface oxidized region creates the residual compressive stress, which increases the strength and the fracture toughness.
High temperature tensile tests were carried out at various displacement rates. The main results obtained are as follows. (1) Fracture strength decreased sharply at temperatures beyond 1000°C. (2) No non-linear load-displacement relation was observed at a displacement rate equal to 0.6mm/min at either 900°C or 1000°C. Under these test conditions, high temperature slow crack growth (H.T. SCG), which is creep damage, was not observed and fracture originated from the defects such as pores or inclusions. (3) Non-linear load-displacement relation was observed at a displacement rate equal to or smaller than 0.06mm/min at 1100°C. Non-linear deformation increased as the displacement rate decreased. In this case, high temperature slow crack growth was observed and fracture originated mainly from high temperature SCG. (4) Fracture strength at 900°C was dominated by either defects such as pores or high temperature damage. Softening of the glass phase due to O2- diffusion at this temperature may be attributable to this damage. Creep damage appeared at temperatures equal to or higher than 1100°C. At 1200°C, fracture strength was mainly dominated by creep damage.
Much interest in new alloys is being taken at present. The improvement by chemical yeast has almost reached the limit for developing a superalloy used for high-temperature components. Accordingly, attention is being paid to the progress of directionally solidified and single crystal casting processes. High-temperature strength of a single crystal superalloy is superior to those of conventionally and directionally solidified cast ones for the following reasons: (1) A high incipient melting temperature by not intentional adding grain boundary strengthening elements, (2) High creep strength by a high gamma prime solution temperature, and (3) Improved properties by a high solution heat treatment temperature. This paper describes an experimental study on the creep-fatigue strength of a Ni-base single crystal superalloy, CMSX-2, for the purpose of applying it to turbine blade and vane in a coal-gasification combined-cycle plant. The experimental results displayed clearly the following points: (1) The lives under PP strain wave became longer in comparison to those under other strain waves, PC, CP and CC. (2) CMSX-2 has excellent creep-fatigue strength in comparison to those of Ni-base conventionally and directionally solidified cast superalloys, Mar-M247. (3) The creep-fatigue strength of CMSX-2 could be sensitive to the gamma prime size, especially under PP strain wave.
This paper examines a life prediction method for a low strengh and high ductility material, cast Co base superalloy (10Ni-29Cr-7W-0.2Ti-0.25Nb-0.15Zr-0.40C-Co), under fatigue-creep interaction (FCI) conditions. We previously proposed a frequency modified total strain energy parameter to evaluate failure lives (Nf), crack initiation lives (Nc) and surface crack propagation behavior for high strength superalloy under FCI conditions. The frequency modified total strain energy parameter was obtained from the total tensile strain energy (ΔWTT) and loading time (τTT) under tensile stress. This paper examines the suitability of applying the frequency modified total strain energy to life prediction and crack propagation behavior evaluation for cast Co base superalloy. We have found that not only crack initiation and failure lives, but also crack propagation behavior of cast Co base superalloy under FCI conditions can be estimated exactly by using the frequency modified total strain energy parameter.
This paper is concerned with the crack propagation due to stress corrosion cracking in glass fiber reinforced plastics (GFRP) under acid environments. As a result of previous works, it is well-known that, based on linear elastic fracture mechanics, the relationship between the crack propagation rate da/dt in GFRP under acid environments and the stress intensity factor K at the crack tip is expressed in the form da/dt=AKm where A and m are constants. This relationship has been established experimentally and no literature has dealt with the theoretical examination of the relationship. In this paper, the micromechanics study has been made on the relationship by using the model of crack propagation due to stress corrosion cracking in GFRP proposed by Hull et al. It is shown that the relationship can be theoretically derived, and the effects of experimental conditions and the material constants of glass fiber on the crack propagation rate are clarified.
The blast erosion behavior of epoxide composites was investigated by using a blasting apparatus with Al2O3 particles and compared with that of epoxide resin with no filler. Three kinds of Al2O3 powders with the average particle size of 0.66, 5.7 and 24.2μm were used as the filler. The experimental results showed that the lower the ductility of epoxide composites, the higher was the volume erosion rate. The erosion damage peak of epoxide composites existed at nearly 30° of blast angle and the main erosion mechanisms were observed to be cutting and cracking-like detachment. It is considered that the blast erosion behavior of epoxide composites with Al2O3 filler may be mainly determined by the fracture toughness. It is also shown that the tensile strength of epoxide composites can be estimated simply by fracture mechanics analysis, based on the assumption of flaw introduction effect by Al2O3 filler.
The effect of repeated in-service inspections on the reliability degradation due to fatigue crack growth is investigated based upon a stochastic fracture mechanics. A method to evaluate the failure probability under repeated inspections is first discussed on the assumption that the component is exchanged when cracks are detected. The results are then applied to investigate how the reliability of structures behaves under repeated ultrasonic inspections. It is clarified that the inspection policy and the stochastic nature of the fatigue crack propagation process have significant effects on the reliability degradation of the structural component.
The concentration and diffusion coefficient of hydrogen in palladium films coated on iron have been measured by an electrochemical method. Palladium films were deposited by RF sputtering. In the cases of film thickness of 0.05-1.36μm and specimen thickness of 0.1-0.8mm, most of hydrogen absorbed in the specimen were dissolved in the palladium film, and hydrogen permeation through the specimens with thin film layers was governed by permeation through iron. The solubility of hydrogen in the film was nearly equal to that in an annealed bulk specimen of palladium. The diffusion coefficient of hydrogen was 4.3×10-13m2/sec in the film of α-phase at 298K, which was about 2 orders of magnitude lower than that in the bulk specimen.
Tetragonal zirconia polycrystals stabilized by Y2O3 (Y-TZP) are recognized as a high strength material. However, Y-TZP has a fatal degradation at relatively low temperatures (100-300°C) according to the transformation from tetragonal to monoclinic phase. This transformation was reported to depend on the grain size in the sintered body. The purpose of the present study was to clarify the relationship between the properties of the starting powder and the low-temperature degradation of sintered specimens. The process and the results are as follows. (1) The fine raw powders of zirconia with specific surface area of 10, 20 and 30m2/g were prepared by hydrolysis of ZrOCl2·8H2O and Zr(OH)4, coprecipitation of hydrated ZrO2 and Y(OH)3 by NH4OH, and calcination in the temperature range of 800-1100°C. (2) These raw powders having specific surface area of 20 and 30m2/g could be sintered easily at 1300°C and yielded the sintered bodies with small grain sizes. In these samples, the degradation could be scarcely observed even under a 200°C hydrothermal condition. (3) The degradation in bending strength of Y-TZP by aging in hot water of 200°C showed good correspondence with the increase of monoclinic phase by the aging. (4) When Y2O3 content and bulk density were fixed, the degradation behavior was closely related to the grain size of the sintered body. The critical grain size of the phase transformation from tetragonal to monoclinic was about 0.3-0.4μm.
Several surface modified ultrafine silica powders have been prepared by a dehydration-condensation reaction between a hydroxy (silanol) group on the surface of silica and a normal-alkyl chain group of different alcohols. By comparing the adsorption isotherms of water molecules on the differently modified silica surfaces, the one-to-one correspondence in water adsorption was found between water molecules and residual surface silanol groups within the range of relative water vapor pressure (P/P0) in the formation of monomolecular adsorption layer on the silica surface. It was found that such a long chain of alkyl groups as normal-octyl or dodecyl groups can make the silica surface hydrophobic preventing from capillary condensation at an interparticle space, even at a small degree of alkyl group substitution (0.3-0.4 groups/nm2) due to a great increase of an effective molecular occupation area of substituted alkyl chain groups. It was evidentially pointed out that the bound water of at least two to four molecular layers adsorbed on the silica surface exists in an energetically more stable state due to structurization of water molecules in the layers than normal water being depressed in its freezing point.
Three kinds of fiducial microgrids with ion etched groove, deposited gold and deposited platinum lines were made on creep specimens by electron lithography using a usual scanning electron microscope, and assessed for high temperature use, particularly for the measurements of micro deformation during creep. The assessment showed that the microgrid with ion etched groove lines is most stable at high temperatures and suitable for the measurement of local micro deformation such as the grain boundary sliding. Using the microgrid with ion etched groove lines, the grain boundary sliding during creep in a 321 stainless steel was measured, and an effect of grain boundary triple point on the sliding and the morphologies of grain boundary cracks at surface were studied quantitatively and geometrically, respectively. It was suggested that the formation of a micro crack at the triple point allows the sliding easily, while a flawless triple point arrests the sliding evidently. Also it was confirmed that geometrical factors such as the morphologies and size of the surface cracks are controlled mainly by the direction and amount of the sliding.
The variability of fatigue crack growth rate da/dN should be decomposed into two parts; the inter-specimen variability and the intra-specimen one. Recently, the inter-specimen variability is considered to be more important than the intra-specimen one from a reliability engineering point of view. In order to analyze the statistical prosperity of inter-specimen variability, fatigue crack growth tests must be conducted under the constant ΔK condition and the crack length must be measured at intervals of constant cycles, because the inter-specimen variability depends upon the intervals between measurements of crack length. Then an automated testing system is strongly needed for those statistical analysis. However, it is considered to be difficult to guarantee the measurements of crack length at regular intervals with single task processing, because the process of saving data in floppy disk or managing key-board may force the process of measuring crack length to wait. Thus an automated fatigue crack growth rate testing system using real-time multitask processing has been developed, which enables us to measure crack length at regular intervals. This paper describes in detail a personal computer-based testing system designed to be used with a standard servo-hydraulic test frame. A new algorithm is introduced to perform constant ΔP and constant ΔK fatigue crack growth tests effectively using a multi-tasking method. The system is designed to ease of operation and reduce the chance of operator error. The developed system was examined for the constant ΔK test and the satisfactory results were obtained. In this paper an error analysis was also performed to determine the crack length error. The analysis clarified the effect of an error in load and back face strain on determination of compliance-inferred crack length.