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Effect of heat-affected zone (HAZ) on spot weldability in automotive hot stamping (HS) steel sheet was investigated for automotive applications. Tensile test was performed on a tensile testing machine at a crosshead speed of 3 mm/min, using spot welded test specimen (Parallel length: 60 mm, Width: 20 mm, Thickness: 1.4 mm, Tab: 20×20 mm). The spot welding test was carried out using spot welded test specimen with welding current (I) of 6.3 kA to 9.5 kA. Hardness was measured with the dynamic ultra micro Vickers hardness tester. In HS steel, has very high strength of 1 500 MPa, tensile strength (TS) and total elongation (TEl) of the spot welded test specimen of HS steel were lower than those of base metal test specimen. The spot welded test specimen broke in the weld. The Vickers hardnesses (HVs) of base metal and fusion zone of hot stamping steel were around HV500. In addition, the hardness of HAZ was under HV300. The difference of hardness between fusion zone and HAZ was around HV200. The hardness distribution acted as a notch. On the other hand, in dual phase (DP) steel, has low strength of 590 MPa, the TS of spot welded test specimen of DP steel was the same as the base metal test specimen because of the breaking of base metal. The TEl of the spot welded test specimen of DP steel was smaller than that of base metal test specimen. In the spot welded test specimen of DP steel, the hardness of base metal was around HV200 and the fusion zone was around HV500. The hardness distribution did not act as a notch. The difference in hardness between base metal and HAZ acted on a crack initiation at HAZ softening.

This paper presents an experimental and analytical investigation of the effect of specimen geometry on the tensile properties and damage behavior of glass fiber reinforced polymer woven laminates at cryogenic temperatures. Cryogenic tensile tests were performed on three types of specimens, and acoustic emission monitoring was employed to characterize the damage development during loading. A two-dimensional finite element analysis was also carried out for three tensile test specimens in order to have a thorough understanding of the progressive failure behavior. A comparison was made between simulation and experiment.

The theory of ferromagnetic elastic materials of multidomain structure is applied to develop a crack growth rate equation of a finite crack in a soft ferromagnetic material under mode I tensile loading and uniform magnetic field. The plane strain and plane stress problems are considered. Dugdale’s assumption regarding the plastic zone in metals is applied to estimate the effect of yield around the crack tip. The accumulated plastic displacement criterion is used for developing a solution for the crack growth rate. Numerical values of crack growth rate are obtained for a soft ferromagnetic strip with a single-edge crack and the results are displayed graphically. Crack growth rate tests are also conducted on nickel–iron soft magnetic materials with a single-edge cracked plate specimen geometry in the bore of a superconducting magnet, and a comparison is made between numerical results and experimental data.

This paper relates to experimental and analytical work on the cryogenic tensile and damage behavior of glass fiber reinforced polymer woven laminates. Tensile tests were performed on specimens with gradual transition region at room temperature, 77, 20, and 4 K. During the tensile tests, acoustic emission monitoring was employed to characterize the damage development. A two-dimensional finite element model was also used to perform the progressive failure analysis.

This paper focuses on understanding the tension–tension fatigue behavior of woven glass fiber reinforced polymer laminates at cryogenic temperatures. Tension–tension fatigue tests at frequencies of 4 and 10 Hz with a stress ratio of 0.1 were conducted at room temperature, 77 and 4 K. The fatigue stress versus cycles to failure ( S – N ) relationships and fatigue limits for 10 6 cycles were obtained. Fractured specimens tested under fatigue tests were also examined with optical microscope.

The cryogenic fatigue delamination behavior of glass fiber reinforced polymer woven laminates under Mode I loading has been investigated experimentally and numerically. Fatigue delamination tests were conducted using double cantilever beam specimens at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). Fracture surface examination using scanning electron microscopy revealed delamination mechanisms under fatigue loading. A finite element analysis was also employed to calculate the J-integral range and damage distributions. The effects of temperature and loading condition on the fatigue delamination growth rates were discussed.

This paper deals with mode III delamination properties of glass fiber reinforced polymer woven laminates at room temperature (293 K), liquid nitrogen temperature (77 K), gas helium temperature (20 K), and liquid helium temperature (4 K). In order to evaluate these properties, the Split Cantilever Beam (SCB) fracture test is performed. The load is applied to a test specimen through a set of identical grips in order to reduce (in some degree) the mode II loading at the free edges. A three-dimensional finite element analysis is used to study the stress and strain state of the specimens and to interpret the experimental measurements. The strain energy release rate is calculated by using the virtual crack closure technique. It is found that the strain energy release rate is dominated by the mode III component. A non-uniform distribution of the strain energy release rate along the delamination front is obtained with mode III component having maximum at the center of the delamination front, while mode II component increases towards the free edges. The strain energy release rate is also determined using the crack closure technique. A finite element analysis is also carried out to calculate the stress intensity factors for the SCB specimens. The fracture surfaces are examined by scanning electron microscopy to identify the fracture mechanisms. The most important conclusion from the present study is that at temperature lowering from 293 to 20 K the mode III fracture toughness increases, further cooling to 4 K produces a toughness decrease.

This paper applies the theory for magnetoelasticity to solve the plane problem of an edge crack in a soft ferromagnetic half-plane subjected to a far-field tension and a uniform magnetic field. Fourier transform techniques are used to formulate the mixed boundary value problem as a singular integral equation. The stress intensity factor is calculated and is shown graphically. Tensile tests are also performed on a cracked ferromagnetic plate with strain gage technique, and the numerical results are compared with the test data.

This paper presents results from an analytical and experimental study of the effect of temperature and mixed-mode ratio on the interlaminar fracture toughness in glass-cloth∕epoxy laminates. Mode I, mode II, and mixed-mode tests were conducted by the double-cantilever beam, end-notched flexure, and mixed-mode bending test methods at room temperature, liquid nitrogen temperature (77 K), and liquid helium temperature (4 K). A finite element model was used to perform the delamination crack analysis. Mode I, mode II, and mixed-mode energy release rates at the onset of delamination crack propagation were computed using the virtual crack closure technique. The fracture surfaces were examined by scanning electron microscopy to correlate with the interlaminar fracture properties.

This paper examines the effects of test specimen size on the cryogenic fracture toughness properties of a nitrogen-strengthened austenitic stainless steel for superconducting magnet structures in fusion energy systems. Single-specimen J-integral tests were performed on CT (compact tension) specimens with and without side-grooves in liquid helium at 4 K. The aspect ratio (specimen width to thickness) and thickness were varied. A three-dimensional finite element analysis was also conducted to investigate the effects of specimen thickness and side-groove on the through thickness distributions of the J-integral values. The results of the finite element analysis are used to supplement the experimental data.

The magnetoelastic plane problems of an infinite soft ferromagnetic strip containing two symmetric edge cracks normal to the boundary are formulated in terms of a singular integral equation. The main purpose of the paper is to investigate the effect of magnetic fields on the stress intensity factors. The solutions of the problems are obtained for a uniform magnetic field normal to the crack surfaces and for uniaxial tension applied to the strip away from the crack region. A strain gage method is also employed in tensile tests to determine the magnetic stress intensity factors. The theoretical results for the plane stress case agree very well with the experimental values.

Single-edge precracked-beam (SEPB) tests were performed on a commercial lead zirconate titanate (PZT) ceramic. Mechanical loading was applied by the crosshead displacement control of a screw-driven electromechanical test machine. The fracture toughness parameter K C was determined for various electric fields. A finite element analysis was also done to calculate the total potential energy release rate, mechanical strain energy release rate, and stress intensity factor for three-point flexure piezoceramic specimens with permeable and impermeable cracks under displacement and load control conditions. Numerical investigation and comparison with test data indicate that the energy release rate, upon application of the permeable model, is useful for predicting crack growth in PZT ceramic under electromechanical loading. Based on current findings, we suggest that the energy release rate criteria for the permeable crack are superior to fracture criteria for the impermeable crack.

This paper presents the results of a study on the effect of magnetic fields on the moment intensity factors in the through-cracked soft ferromagnetic plates with fixed ends. The experiments were conducted on a ferritic stainless steel with the through-cracked plate specimen geometries in a uniform, static transverse magnetic field. Strain gages were used to evaluate the magnetic-moment intensity factors. The experimental results were given for a single-internal crack, a single-edge crack, and two symmetric-edge cracks. The magnetic-moment intensity factor estimated from the measured strains was in good agreement with the theoretical calculations based on the authors’ previous work.

The effects of applied voltage on the electroelastic field concentrations ahead of electrodes in multilayer piezoelectric actuators were examined in a combined experimental and numerical investigation. Experiments were performed to measure the strain near internal and surface electrodes at various electrical loading conditions. The finite element method was also used to solve the coupled electro-elastic boundary value problem. The strain, stress and electric displacement concentrations were calculated and a non-linear behavior induced by localized polarization switching was discussed. A comparison of strain concentration was made between experiment and simulation.

This paper presents the results of an experimental and theoretical investigation of the magnetic fracture behaviour of double cantilever beam (DCB) specimens. DCB tests were conducted on ferritic stainless steel SUS430 in the bore of a superconducting magnet at room temperature. A simple experimental technique using strain gauges was used to determine the stress intensity factor. The experiments show the predicted increase in the stress intensity factor with increasing magnetic field. The theoretical analysis is based on a beam-plate theory for magnetoelastic interactions in a soft ferromagnetic material. Numerical calculations are carried out, and the stress intensity factor is obtained for several values of magnetic field. A comparison of the stress intensity factor is made between theory and experiment, and the agreement is good for the magnetic field considered.

To evaluate the tensile properties of SL-ES30 glass-cloth/epoxy laminates for superconducting magnets in fusion energy systems, tensile tests were examined both experimentally and analytically. The tensile tests were conducted in accordance with JIS K 7054 at room temperature and liquid nitrogen temperature (77 K). The general specimen geometry was a rectangular dog-bone shape with constant gage length but with each specimen size having a different specimen width. The experimental finding provides the data for analytical modeling. The model utilizes two damage variables that are determined from experimental data. A finite-element method coupled with damage was adopted for the extensional analysis. The effects of temperature, specimen geometry, and gripping method on the tensile properties are examined.

The electroelastic field concentration due to circular electrodes in piezoelectric ceramics has been discussed through theoretical, numerical and experimental characterizations. This paper consists of two parts. In the first part, the problem of a surface electrode attached to a semi-infinite piezoelectric solid was formulated by means of Hankel transforms and the solution was solved exactly. The displacements and electric potential were expressed in closed form. In the second part, finite element analysis was carried out to study electroelastic fields in piezoelectric disks containing circular electrodes of different radii by introducing a model for polarization switching in local areas of electroelastic field concentration. A nonlinear behavior induced by localized polarization switching was observed between the strain and the voltage applied to the electrode. Experiments were also conducted to study the strain state near the electrode tip. Comparison of the predictions by the present model with experimental data is conducted and pertinent conclusions are drawn. This work is the first attempt to obtain nonlinear electroelastic fields around a circular electrode in piezoelectric ceramics and validate the polarization switching model.

The fracture behavior of a piezoelectric ceramic under applied electric fields has been discussed through experimental and theoretical characterizations. The modified small punch (MSP) tests were performed on a commercial piezoelectric ceramic. The fracture initiation loads under different electric fields were obtained from the experiment. Fracture surface was examined for the MSP specimens to identify the failure mechanisms under high electric fields. A nonlinear three-dimensional finite element analysis was also employed to calculate the fracture deflection and MSP energy. A procedure is presented for determining the fracture and polarization switching properties due to electrical effects by experimental and theoretical means.

The present paper includes experimental and analytical data on the fracture properties of a nickel–iron superalloy, a ferromagnetic austenite, at 4 K in magnetic fields of 0 and 6 T. The tensile, notch tensile and small punch tests are employed. A finite element analysis is also performed to convert the experimentally measured load–displacement data into useful engineering information. To interpret the results we review the available theory of the influence of magnetic field on the stress intensity factor for a crack in ferromagnetic materials.

The results of an experimental and theoretical investigation of the bending behavior of a soft ferromagnetic cantilever beam-plate in a transverse magnetic field are presented. The theoretical model based on a beam-plate theory for magneto-elastic interactions in a soft ferromagnetic material predicts the deflection and strain for several values of the magnetic field and the geometrical parameter. The experiments were conducted on ferritic stainless steel SUS430 in the bore of a superconducting magnet at room temperature. The experiments show the predicted increase in the deflection and strain with increasing magnetic field. The theoretical results agree very well with the experimental data.

In order to evaluate the mechanical properties of T800H/3633 CFRP woven laminates for cryogenic tankage in RLV, tensile and in plane shear tests were performed at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). The tensile tests were conducted in accordance with ASTM D 3039 and JIS K 7073. Tensile strength and modulus were evaluated for both the warp and fill directions. A problem was encountered with obtaining acceotable failure of the specimens. We could not achieve failure in the test section. This problem was avoided by using dogbone shaped specimens. A two dimensional finite element analysis was also used to study the stress distributions within the specimens and to interpret the experimental measurements. The in-plane shear modulus and shear strength were measured by tensile tests on the ±45' specimens (ASTM D3518 and JIS K 7079). The effects of temperature on the stress-strain responses in tension and in plane shear are examined. Fracture topography of specimens is also investigated and interpreted.

This paper discusses the fracture and the adiabatic heating of austenitic stainless steels that may be used in cryogenic structures for the superconducting magnets of magnetic fusion reactors. Elastic–plastic fracture toughness tests were performed on compact specimens in liquid helium at 4 K. Adiabatic heating was detected by measuring the internal temperature. The effect of test specimen size and side grooving on the cryogenic fracture toughness, and the temperature rise during dynamic crack growth are examined. A size independent toughness parameter results in the case of side-grooved specimens. The effect of inclusion content on the fracture mechanics parameters is also discussed.

This paper deals with the scattering of time harmonic flexural waves by a through crack in a magnetically saturated plate under a uniform magnetic field normal to the plate surfaces. The analysis is based on Mindlin's plate theory of magneto-elastic interactions under a magnetic field. An incident wave giving rise to moments symmetric about the crack plane is applied. Fourier transforms are used to reduce the mixed boundary value problem to one involving the numerical solution of a Fredholm integral equation. The dynamic moment intensity factor versus frequency is computed and the influence of the magnetic field on the normalized values is displayed graphically.

The bending of through-cracked ferromagnetic plates in a static magnetic field is investigated to show the effect of induced magnetization. A simple experimental technique employing strain gages is used to determine the magnetic moment intensity factor. The theoretical results agree very well with the experimental data. The scattering of time harmonic flexural waves by a through crack in an infinite plate under a uniform magnetic field is also studied.

To estimate the electric fracture toughness, indentation fracture (IF) tests were made on piezoelectric materials under combined mechanical and electrical loads. Lead zirconate titanate (PZT) ceramics from a commercial source were used. A three-dimensional finite element analysis was also employed to calculate the energy release rate and stress intensity factor. Surface cracks produced by indentation with Vickers indented were modeled as two point-force loaded half-penny-shaped cracks.

A simple experimental procedure involving measurement of strain through strip gages with five strain sensors per strip gage, has been developed to determine magnetic moment intensity factors in different specimen geometries. Static experiments are conducted in the bore of a superconducting magnet at room temperature. Ferritic stainless steel is here used as the fixed-end through-cracked plate specimen for bending test. The experiments show the increase in the moment intensity factor with increasing magnetic field. The effect of the magnetic field on the moment intensity factor is more pronounced with increasing the crack length to specimen thickness ratio. The qualitative experimental trends are in good agreement with the theoretical model developed previously.

An experimental and analytical investigation in cryogenic Mode I interlaminar fracture behavior and toughness of SL-E woven glass-epoxy laminates was conducted. Double cantilever beam (DCB) tests were performed at room temperature (R.T.), liquid nitrogen temperature (77 K), and liquid helium temperature (4 K) to evaluate the effect of temperature and geometrical variations on the interlaminar fracture toughness. The fracture surfaces were examined by scanning electron microscopy to verify the fracture mechanisms. A finite element model was used to perform the delamination crack analysis. Critical load levels and the geometric and material properties of the test specimens were input data for the analysis which evaluated the Mode I energy release rate at the onset of delamination crack propagation. The results of the finite element analysis are utilized to supplement the experimental data.

Consider the impingement of time harmonic flexural waves on a through crack in a soft ferromagnetic plate the surface of which is subjected to a uniform magnetic field at normal incidence. Mindlin's plate theory is used to account for the magneto-elastic interaction. For an incident wave that gives rise to moments symmetric about the crack plane, Fourier transforms are applied reducing the mixed boundary value problem to a Fredholm integral equation that can be solved numerically. The dynamic moment intensity factor versus frequency is computed to exhibit the influence of the magnetic field.

This paper investigates the use of circumferentially notched bar specimens for the measurement of elastic-plastic fracture toughness (J 1C ) of structural alloys and weldments for superconducting magnets in fusion energy systems. Notch tensile tests were performed with small cylindrical notched bar specimens at liquid helium temperature (4 K) using crosshead rates of 0.2 mm/min and 20 mm/s. Test specimens were 5 mm in diameter with a 30-mm reduced section. In the mid-section of the specimen a 1 mm deep electro discharge machined (EDM) notch of 0.2 mm width was machined around the girth, thus maintaining a starting diameter of 3 mm. Correlations between notch tensile strength (σ NTS ), failure energy absorption (E NT ), and J 1C were assessed. The best data fit was found between the ratio σ NTS /J 1C and J 1C . A finite element analysis was also performed to compute directly the J-values. Comparisons of the predicted J 1C with results obtained from conventional JIS Z 2284 standard tests were made. Results of structural alloy weldment with a representatively wide range of J 1C indicate that fracture toughness prediction accuracy is roughly equal to ±25 percent.

Cryogenic interlaminar beam tests in the form of three-point flexure are examined both experimentally and analytically. The use of the short-beam shear test for measuring the interlaminar shear strength of glass-cloth/epoxy laminates at low temperatures is evaluated first. The interlaminar shear tests were carried out with short-beam shear specimens at room temperature, 77 K and 4 K to evaluate the interlaminar shear strength of G-10CR glass-cloth/epoxy laminates. Each specimen was placed on two roller supports that allow lateral motion and a load was applied directly at the center of the specimen. These tests were conducted in accordance with ASTM, 1984, “Standard Test Method for Apparent Interlaminar Shear Strength of Parallel Fiber Composites by Short-Beam Method,” Designation D2344-84. The effects of temperature, specimen width, and span-to-thickness ratio on the apparent interlaminar shear strength are shown graphically. Photomicrographs (scanning electron micrographs, optical micrographs) of actual failure modes were utilized to verify the failure mechanisms. A three-dimensional finite element analysis was also performed to investigate the effects of specimen width and span-to-thickness ratio on the shear stress distribution in the mid-plane. Effective elastic moduli were determined under the assumption of uniform strain inside the representative volume element. The numerical findings are then correlated with the experimental results.

The cryogenic interlaminar fracture toughness of woven glass-epoxy laminates was measured under mode I loading using double cantilever beam (DCB) tests. The tests were performed at room temperature (R. T.), liquid nitrogen temperature (77K) and liquid helium temperature (4K) to evaluate the effect of temperature and geometrical variations on interlaminar fracture toughness. The fracture surfaces were examined by scanning electron microscopy to verify the failure mechanisms. A finite element model was used to perform the delamination crack analysis. The results of the finite element analysis are utilized to supplement the experimental data.

In order to evaluate the cryogenic compressive properties of G-10CR and SL-ES30 glass-cloth/epoxy laminates for superconducting magnets in fusion energy systems, compression tests were performed at room temperature (RT), liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). The effects of temperature and specimen geometry on the compressive properties are examined. Photomicrographs of actual failure modes were utilized to verify the failure mechanisms.

The cryogenic interlaminar shear behavior of G-10CR glass-cloth/epoxy laminates has been discussed through theoretical and experimental characterizations. The use of the double-notch shear test for measuring the interlaminar shear strength of glass-cloth/epoxy laminates at low temperatures is evaluated first. The interlaminar shear tests were carried out with double-notch shear specimens at room temperature, 77 K and 4 K to evaluate the interlaminar shear strength (ILSS) of G-10CR glass-cloth/epoxy laminates. The double-notch shear specimen was loaded on its ends in compression with a supporting jig to prevent buckling. These tests were conducted in accordance with ASTM D3846-79. The effects of temperature, specimen thickness, and notch separation on the apparent ILSS are shown graphically. Fracture surfaces were examined by scanning electron microscopy (SEM) and optical microscopy to verify the failure mechanisms. A three-dimensional finite element analysis was also performed to investigate the effect of specimen thickness and notch separation on the shear stress distribution in the expected fracture plane. Effective elastic moduli were determined under the assumption of uniform strain inside the representative volume element. The numerical findings are then correlated with the representative volume element. The numerical findings are then correlated with the experimental results. The validity of this test technique has been established.

Following a classical plate bending theory of magneto-elasticity, we consider the crack problem of a soft ferromagnetic plate under a uniform magnetic field. By the use of Fourier transforms we reduce the problem to solving a pair of dual integral equations. The solution of the dual integral equations is then expressed in terms of a Fredholm integral of the second kind. The bending moment intensity factor is computed and the influence of the magnetic field on the normalized values is displayed graphically.

In order to evaluate the cryogenic compressive properties of G-10CR and SL-ES30 woven glass-epoxy laminates for superconducting magnets in fusion energy systems, compression tests were performed at room temperature (R. T.), liquid nitrogen temperature (77K) and liquid helium temperature (4K). These tests were conducted in accordance with JIS K 6911 and JIS K 7056. Compression specimens of G-10CR with different specimen length to cross-sectional area ratios were tested in the normal direction (normal to the glass cloth). Compression specimens of SL-ES30 with different specimen length to cross-sectional area ratios were also tested in the warp, fill and normal directions. The effects of temperature and specimen geometry on the compressive properties were examined. Photomicrographs of actual failure modes were utilized to verify the failure mechanisms.

Summary JJ1 type austenitic stainless steel is emerging as the preferred structural material for nuclear fusion reactor superconducting magnet casings designed to operate at the temperature of liquid helium (4 K). To evaluate the cryogenic fracture toughness and temperature rise of tungsten inert gas (TIG) welds in 200 mm thick forged JJ1 type austenitic stainless steel plate for the next generation of nuclear fusion reactor superconducting magnets, clastic-plastic fracture toughness (J1C) tests were conducted with 1T compact tension specimens at 4 K. The tests were conducted to ASTM E813–87 standard specifications for determination of J1C by the unloading compliance technique to monitor crack growth. Au/0.07%Fe-chromel thermocouples were used to measure the temperature rise near the crack tip. The effects of the specimen sampling position and nitrogen content on J1C are examined. Specimens were examined by scanning electron microscopy (SEM) after fracture testing. The effect of the inclusion content on t...

Experimental evidence and theoretical analysis are presented for the bending of a soft ferromagnetic beam plate in a magnetic field. The experiments were conducted in the bore of a superconducting magnet at room temperature. Ferritic stainless steel SUS 430 is here used as the cantilever specimen for bending test. The experiments show the predicted increase in the deflection and strain with increasing magnetic field. The theoretical analysis is based on a classical plate bending theory for magneto-elastic interactions in a soft ferromagnetic material. Numerical calculations are carried out, and the deflection and strain are obtained for several values of magnetic field and geometrical parameter. A comparison of the deflection and strain is made between theory and experiment and the agreement is good for the magnetic field considered.

In order to evaluate the cryogenic fracture toughness and the temperature rise of G-10 woven glass-epoxy laminates, plane-strain fracture toughness testing was performed with 0.4T compact tension specimens at room temperature, 77K and 4K. Testing was conducted in accordance with ASTM standard E399-83 and JSME standard S001 for determining the fracture toughness. Chromel-vs-Au/0.07% Fe thermocouples were used to measure the temperature rise near the crack tip. The effects of temperature, crack length and crosshead speed on the fracture toughness are examined. The damage morphology around the crack tip of tested specimens was characterized using scanning electron microscopy (SEM).