Showing papers on "Residual stress published in 1984"

Measurement of adherence of residually stressed thin films by indentation. I. Mechanics of interface delamination

Abstract: A fracture analysis of indentation‐induced delamination of thin films is presented. The analysis is based on a model system in which the section of film above the delaminating crack is treated as a rigidly clamped disc, and the crack extension force is derived from changes in strain energy of the system as the crack extends. Residual deposition stresses influence the cracking response by inducing buckling of the film above the crack and by providing an additional crack driving force once buckling occurs. A relation for the equilibrium crack length is derived in terms of the indenter load and geometry, the film thickness and mechanical properties, the residual stress level, and the fracture toughness of the interface. The analysis provides a basis for using controlled indentation cracking as a quantitative measure of interface toughness and for evaluating contact‐induced damage in thin films.

On the estimation of the Weibull modulus

Abstract: It is well documented that nominally identical specimens of brittle materials, e.g. ceramics, show a large variation of tensile fracture stresses and in order to use brittle materials as engineering materials the strength has to be characterized. The most widely used expression for characterization is the cumulative distribution function proposed by Weibull [ 1 ]. The Weibull function is also known to statisticians as Fisher-Tipper Type Ill distribution of smallest values or as the third asymptotic distribution of smallest extreme value [2]. The Weibull statistics is based on the the "weakest link-hypothesis" which means that the most serious flaw in the specimen will control the strength. The most serious flaw is not necessarily the largest one because its severity also depends on where it is situated. In other words, the flaw which is subjected to the highest stress intensity factor will be strength controlling. The flaws initiating fracture can conveniently be classified as intrinsic or extrinsic [3]. The intrinsic flaws are introduced during fabrication and are predominantly inclusions and voids. The extrinsic flaws are stress-induced cracks, such as surface cracks introduced during machining and microcracks resulting from large residual stresses, e.g. due to thermal contraction

Mechanisms of Failure from Surface Flaws in Mixed‐Mode Loading

Abstract: Mechanisms of failure from surface cracks in combined tension and shear are identified by directly observing the cracks during failure testing. Under the combined influences of residual contact stresses and applied loading, indentation cracks propagate stably and realign normal to the principal applied tension prior to failure. Annealing of indentation flaws causes relaxation of the residual stresses and thereby leads to a change in the mechanics of fracture; unstable propagation occurs from the initial crack at a critical applied loading, with an abrupt change in fracture plane. Strengths of indentation flaws and machining damage in both the as-formed and annealed states are measured as a function of flaw orientation relative to an applied uniaxial tension. Strength variations of indentations and machining flaws are similar. The results are assessed in terms of various proposed mixed-mode fracture criteria, and the implications of the results for nondestructive testing using scattering of surface acoustic waves are discussed.

Measurements of adherence of residually stressed thin films by indentation. II. Experiments with ZnO/Si

Abstract: Indentation‐induced delamination between thin films of ZnO and Si substrates is examined. Delamination occurs by the growth of lateral cracks, either along the interface or within the film adjacent to the interface. The crack path is determined by the indenter load and the film thickness, as well as by residual stresses formed during deposition. A change in crack path from the interface to the film, accompanied by an increase in crack radius, is observed and is interpreted as a buckling‐induced stress intensification. The interface fracture toughness is estimated from the relative crack lengths in the buckled and unbuckled films.

Residual Stress Development in the Injection Molding of Polymers

Abstract: Injection molding is one of the most widely employed methods for the fabri- cating of polymer articles, being characterized by high production rates and accurately dimensioned products. The process includes the flow of polymer melt through a runner system and gates followed by injection into a cold mold, packing under high pressure, and subsequent cooling to solidification. Accordingly, during the injection-molding process the polymer undergoes simultaneous mechanical and therma! influences while in fluid, rubbery, and glassy states. Such effects introduce residual stresses and strains into the final product [1,2], resulting in highly anisotropic mechanical behavior [3–9] and warpage and shrinkage [10–13]. Thus, understanding the factors governing the residual-stress development during molding is of great importance.

Piles in Sand: A Method Including Residual Stresses

Abstract: A method is presented for the analysis of load distribution of piles driven in sand and subjected to static vertical loads. This method is unique in that it considers the existence of residual stresses due to driving. It uses the results of standard penetration tests to obtain the load transfer curves for friction and point resistance. These curves are modeled by hyperbolas which start at the residual friction and residual point pressure for zero displacement. The design method is based on a simple theory and a 33‐pile data base. Since each pile had sufficient instrumentation and a sufficiently complete load test program, the residual stresses and transfer curves could be determined with reasonable accuracy from the data base.

Nondestructive methods for material property determination

Abstract: X-Ray Diffraction and Neutron Scattering Techniques.- X-Rays for Non-Destructive Characterization of Materials Properties.- Application of a Position Sensitive Scintillation Detector to Nondestructive X-Ray Diffraction Characterization of Metallic Components.- Residual Stress Measurements in Ti-6Al-4V and ?-Brass with Sub-Surface Flaws Using X-Ray Diffraction Techniques.- Determination of Residual Stress from Two-Dimensional Diffraction Patterns.- Small Angle Neutron Scattering: An NDE Tool.- Eddy Current and Electrical Conductivity Applications.- Prediction of Laser Irradiated Surface Properties by Eddy Current Method.- Solving for Thermal History and Metallurgical Condition of a Quenched and Aged Aluminum Alloy Through Conductivity and Hardness Properties.- Eddy Current Measurement of Residual Stresses in a Heavy Section Steel Weldment.- Magnetic, Ultrasonic, and Analytical Techniques for Stress and Cold Work Indication.- Solving Internal Stress Measurement Problems by a New Magnetoelastic Method.- Nondestructive Determination of Residual and Applied Stress by Micro-Magnetic and Ultrasonic Methods.- The Need for Analytical/Experimental Orchestrated Approaches to Solve Residual Stress Problems in Real Structures.- Internal Friction of Fe-Based Binary Alloys at High Frequency.- General Ultrasonic Considerations and Applications.- The Inverse Problem in Materials Characterization Through Ultrasonic Attenuation and Velocity Measurements.- Inference of Fatigue Crack Closure Stresses from Ultrasonic Transmission Measurements.- Inference of Compressive Stresses at Joined Interfaces Using Ultrasonic Reflectivity.- Frequency Dependent Properties of Materials Containing a Distribution of Pores and/or Inclusions.- Measurement of Thin Case Depth in Hardened Steel by Untrasonic Pulse-Echo Angulation Techniques.- Ultrasonic Micro Structural Characterization of Crystalline Metals.- Acoustic Emission for In-Process Monitoring and Microstructure Control?.- Use of Ultrasonic Techniques to Assess the Mechanical Properties of Steels.- Determination of Microstructural Parameters by Magnetic and Ultrasonic Quantitative NDE.- Microstructural Characterization of Titanium by Acoustic Microscopy.- Ultrasonic Characterization of Titanium 6211 Weldments.- Measurement of Near-Surface Ultrasonic Absorption by Thermo-Emissivity.- Ultrasonic Characterization of Amorphous Metals, Polymers, and Composites.- Ultrasonic Materials Characterization of Melt Spun Metallic Ribbons.- Application of Ultrasonic Technique to Cure Characterization of Epoxies.- Ultrasonic Measurements of Elastic Moduli of Thermally Cycled Metal Matrix Composite Precursor Wires.- Acousto-Elastic Effect of Stress in Aluminum and Steel.- Effects of Rolled Plate Thickness on Anisotropy, with Application to Acoustic Stress Measurement.- Ultrasonic Shear Wave Measurements of Known Residual Stress in Aluminum.- Rayleigh Wave Measurement of Surface Stresses in Stainless Steel Piping.- Acousto-Elastic Effects in Two Structural Steels.- Relationship Between Stress and Temperature Dependence of Ultrasonic Shear Velocity.- Author Index.

Damage Penetration at Elongated Machining Grooves in Hot‐Pressed Si3N4

Abstract: In hot-pressed Si3N4 subjected to single-point diamond grinding, the damage penetration (c) at low vertical loads (Pv) is approximately related by Pvαc, whereas at high loads the load dependence of the crack length is much greater. The results at low loads are discussed in terms of available analyses. An analysis, based on the combined effect of the residual stresses and contact loads, is presented to model the behavior at high loads.

A note on the influence of residual stress on measured hardness

Abstract: The influence of uniform residual stresses on measured hardness value is investigated experimentally, using samples containing a known cylindrical stress value. It is shown that realistic v...

The effect of a temperature gradient on residual stresses and distortion in injection moldings

Abstract: Distortion of bars injection-molded from polystyrene, polypropylene, and glass-fiber-filled polypropylene and subsequently placed in a temperature gradient has been examined. Residual stress distributions have been measured both for the as-molded state and after annealing in a temperature gradient. In the as-molded state all moldings showed the usual residual stress distribution with compressive stresses near the surface and tensile stresses in the interior. In all three materials it was found that tensile stresses could be developed near to the warmer surface on gradient annealing and that tensile stresses still remained at this surface when the bar was cooled and permitted to bend to restore internal equilibrium. It is shown therefore that in addition to the dimensional changes which occur and which may render the molding unserviceable after temperature gradient annealing, another undesirable change takes place, leaving the molding much more susceptible to fracture from a surface flaw. Uniform annealing is found to be much less likely to cause stress reversal and the stresses remain balanced so that distortion is minimal.

Origin and development of residual stresses induced by laser surface-hardening treatments

Abstract: The variations of residual stresses and microstructures obtained by surface hardening with a 15-kw, continuous-wave CO2 laser on samples of AISI 1045 (C43) and AISI 4140 (40CD4) have been studied.

“Side-wall curl” in high-strength steels

Abstract: A study has been made of “side-wall curl” in a series of low-carbon, HSLA 50 and 80 and DP-80 steels. “Curl” occurs when the sheet metal is drawn into a die cavity, as in the forming of hat-shaped sections. It is found that the curl increases with increasing tensile strength and decreasing thickness of the steels, and that there is no consistent variation of curl with die radius. However, the curl, which is a consequence of residual stresses generated by the forming process, is thought to be influenced by the strain-hardening rate of the material, since this will affect the strain distribution through the sheet thickness. It is shown that, by the imposition of plastic deformation, the curl can be eliminated, as the result of the removal of the nonuniform distribution of residual stresses.

Theoretical analysis of the deflection test used in single-surface oxidation of metallic samples

Abstract: On the basis of the experimental results on deflection obtained by Delaunay during single-surface oxidation of metallic samples, a theoretical analysis of this deflection test was carried out Two important problems were established concerning the physical signification of the oxide stress calculated from the measured deflection and the relation between the oxide adherence and the oxide stress In particular, it appears that the oxide stress level determined by the deflection test is only representative of the stresses relieved by the sample curvature Secondly, spalling of the oxide layer is directly related to the product of the residual stress value by the curvature of the sample Some experimental results, recently obtained, confirm this theoretical analysis

Hydraulically expanded tube-to-tubesheet joints

Abstract: To avoid stress corrosion cracking, a method of producing tube-to-tubesheet joints with low residual stresses was sought. Hydraulic expansion was found to be an acceptable method. In this paper, the experimental and theoretical work done to determine these stresses is presented. The area of interest is the transition region between the expanded and unexpanded sections of tubing. X-ray diffraction, stress corrosion cracking test and strain gaging were the prime measuring techniques used. Extensive use of finite element analysis was also made. In addition, the pull strength, length change, etc., of this type of joint were investigated. 4 references, 8 figures.

Roller contact fatigue study of austempered ductile iron

Abstract: Contact fatigue properties of austempered nodular iron transformed at 230 °C to Rc 45-47 were evaluated using roller contact fatigue tests. At a given load, contact fatigue life of the austempered iron was 35 to 45 pct lower than carburized steel. Shot peening, performed using 1.168-mm diameter Rc 45-55 cast steel balls to Almen strip intensity of 0.006 to 0.008 C, was not beneficial. An increase in the surface compressive residual stress introduced by shot peening was accompanied by surface roughening which lowered the fatigue life by detrimentally influencing the EHD film thickness. Stress induced white etching areas well known to develop in high carbon martensite were found to develop in bainitic microstructure also.

Basic compressive strength of steel plates from test data

Abstract: This paper describes a data-base approach to the ultimate compressive strength of unstiffened plates loaded in uniaxial compression. A total 793 individual test results of plates is surveyed and stored into the Numerical Data-Base for the Ultimate Strength of Steel Structures (NDSS). Statistical assessments are made for the plate test results to compare with the available strength formulas. And the effects of initial imperfections such as residual stress and initial out-of-flatness are discussed. Then strength formulas are proposed for two groups, “with residual stress” and “without residual stress”. to explain more accurately the test data.

Raman Scattering Characterization of Residual Stresses in Silicon-on-Sapphire

Abstract: In order to characterize the residual stresses in silicon-on-sapphire wafers, polarized Raman scattering measurements were made by probing both from the silicon-free surface side and from the silicon/sapphire interface (sapphire substrate) side at three different wavelengths. These measurements are described here. A theoretical consideration of the Raman tensors and frequency shifts in silicon crystals stressed by unknown forces is also given in this paper. It is found that the residual stresses are not uniform, but are distributed in the direction normal to the silicon film plane. The residual compressive stress is relaxed from the interface toward the silicon-free surface with an accompanying shear stress. The residual compressive stress is estimated to be 6.0×108~13.0×108 N/m2 at the silicon/sapphire interface and 5.5×108~7.5×108 N/m2 at the silicon-free surface.

A new method for stress relieving amorphous alloys to improve magnetic properties

Abstract: An analysis of the kinetics of stress relief annealing in amorphous alloys, with particular emphasis on the effect of annealing on the resulting magnetic properties, is made. Based on this analysis, an optimal procedure for annealing amorphous alloy magnetic cores is suggested. It involves a fast heatup to a high temperature for a short time. The expected benefits of this procedure are decreased embrittlement, lower strain induced anisotropy, and lower residual stresses. The conventional technique for stress relieving magnetic cores proved unsuitable for the application of the new annealing treatment. A new technique was devised in which the ribbon is dynamically annealed as it is wound onto the core. The magnetic properties of the resulting toroids are superior to those produced by the conventional technique.

Fatigue threshold studies in Fe, Fe-Si, and HSLA steel: Part I. Effect of strength and surface asperities on closure

Abstract: The fatigue threshold was found to increase as the temperature decreased from 300 K to 123 K for a sequence of Fe and Fe-S binary alloys and an HSLA steel. A prominent closure was observed with the magnitude of closure stress intensity higher at lower temperature. The correlation between closure and threshold stress intensity was examined first with residual plasticity models. With geometrical asperity closure arguments, the closure stress intensity was also correlated with the yield stress and the grain size of the material. By considering the reverse slip, geometry, and oxide-induced closure simultaneously, a model for the closure at fatigue threshold was proposed and compared to the data from this study and the literature. All three mechanisms of residual plasticity, geometrical asperity, and oxide formation are shown to be relevant to the observed closure phenomena in this study.