Ultrasonic emission detector evaluation of strength of bonded materials
Ultrasonic emission detector for nondestructive determination of bond strength
EMISSION SPECTRUM↗
SEARCH · Engineering Papers
Results for “material strength”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Probabilistic lifetime strength of aerospace materials via computational simulation
The results of a second year effort of a research program are presented. The research included development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic phenomenological constitutive relationship, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subjected to a number of effects of primitive variables. These primitive variables often originate in the environment and may include stress from loading, temperature, chemical, or radiation attack. This multifactor interaction constitutive equation is included in the computer program, PROMISS. Also included in the research is the development of methodology to calibrate the constitutive equation using actual experimental materials data together with the multiple linear regression of that data.
Boyce, Lola↗
Effect of Cristobalite on the Mechanical Properties of Silica RSI Materials
The strength of various silica surface insulation materials was measured after high temperature heat treatment to develop substantial crystalline phases, and after low temperature thermal cycling through the alpha-beta cristobalite transformation. It appears that the presence of cristobalite in the structural elements (the fibers) is highly detrimental to tensile strength. When crystallization does not occur in silica material, the strength improves with heat treatment.
Khandelwal, P. K.↗
A practical extension of the recursive multi-fidelity model for the emulation of hole closure experiments
We report in regimes of high strain rate, the strength of materials often cannot be measured directly in experiments. Instead, the strength is inferred based on an experimental observable, such as a change in shape, that is matched by simulations supported by a known strength model. In hole closure experiments, the rate and degree to which a central hole in a plate of material closes during a dynamic loading event are used to infer material strength parameters. Due to the complexity of the experiment, many computationally expensive, three-dimensional simulations are necessary to train an emulator for calibration or other analyses. These simulations can be run at multiple grid resolutions, where dense grids are slower but more accurate. In an effort to reduce the computational cost, a combination of simulations with different resolutions can be combined to develop an accurate emulator within a limited training time. We explore the novel design and construction of an appropriate functional recursive multi-fidelity emulator of a strength model for tantalum in hole closure experiments that can be applied to arbitrarily large training data. Hence, by formulating a multi-fidelity model to employ low-fidelity simulations, we were able to reduce the error of our emulator by approximately 81% with only an approximately 1.6% increase in computing resource utilization.
36 MATERIALS SCIENCE↗
The effects of specimen scale on the compression strength of composite materials
This paper presents a number of observations on the effect of specimen scale on the compression response of composite materials. Work on this topic was motivated by observations that thick-walled, unstiffened carbon reinforced cylinders subjected to hydrostatic pressure were not reaching inplane laminate stress levels at failure expected from coupon level properties, while similar cylinders reinforced with fiberglass were. Results from a study on coupon strength of (0/0/90) laminates, reinforced with AS4 carbon fiber and S2 glass fiber, are presented and show that compression strength is not a function of material or specimen thickness for materials that have the same laminate quality (autoclave cured quality). Actual laminate compression strength was observed to decrease with increasing thickness, but this is attributed to fixture restraint effects on coupon response. The hypothesis drawn from the coupon level results is further supported by results from a compression test on a thick carbon reinforced coupon in a fixture with reduced influence on specimen response and from a hydrostatic test on an unstiffened carbon reinforced cylinder subjected to hydrostatic pressure with end closures designed to minimize their effect on cylinder response.
Camponeschi, Eugene Thomas, Jr.↗
Strength criteria for composite materials (a literature survey)
Literature concerning strength (failure) criteria for composite materials is reviewed with emphasis on phenomenological failure criteria. These criteria are primarily intended to give a good estimation of the safety margin with respect to failure for arbitrary multiaxial stress states. The failure criteria do not indicate the types of fracture that will occur in the material. The collection of failure criteria is evaluated for applicability for the glass reinforced plastics used in mine detectors. Material tests necessary to determine the parameters in the failure criteria are discussed.
Roode, F.↗
An evaluation of the +/-45 deg tensile test for the determination of the in-plane shear strength of composite materials
The applicability of the +/-45 deg tensile test for the determination of the in-plane shear strength of advanced composite laminates is studied. The assumptions used for the development of the shear strength formulas were examined, and factors such as the specimen geometry and stacking sequence were assessed experimentally. It was found that the strength of symmetric and balanced +/-45 deg laminates depends primarily upon the specimen thickness rather than the specimen width. These findings have important implications for the +/-45 deg tensile test which is recommended by several organizations for the determination of the in-plane shear stress/strain response and the shear strength of continuous fiber reinforced composites. Modifications to the recommended practices for specimen selection and shear strength determination are suggested.
Kellas, S.↗
Influence of soft inclusions on the strength of wrought materials
The three dimensional soft particles (such as sulfides, silicates and voids) present in most materials are modelled by circular voids in sheet metal. Relationships are sought between the shape and orientation of a hole after rolling and testing in tension. Then, the effect of hole shape and size on mechanical properties is considered experimentally. The presence of voids has a negligible influence on the ultimate tensile stress of ductile materials based on the unperforated area because plastic flow neutralizes the stress intensification present in the elastic region. However, the shape and orientation of the defects are found to play an important role relative to strain at fracture. In certain engineering applications the strain at fracture is more important than the stress at fracture and in this sense the presence of voids are considered to influence the strength of a ductile material.
Pai, D. M.↗
Strength anisotropy of granular material consisting of perfectly round particles
Abstract The strength anisotropy of granular materials deposited under gravity has mostly been attributed to elongated particles' tendency to align long axes along the bedding plane direction. However, recent experiments on near‐spherical glass beads, for which preferred particle alignment is inapplicable, have exhibited surprisingly strong strength anisotropy. This study tests the hypothesis that certain amount of fabric anisotropy caused by the anisotropic stress during deposition under gravity can be locked in a circular‐particle deposit. Such locked‐in fabric anisotropy can withstand isotropic consolidation and leads to significant strength anisotropy. 2D discrete element method simulations of direct shear tests on circular‐particle deposits are conducted in this study, allowing for the monitoring of both stress and fabric. Simulations on both monodispersed and polydispersed circular‐particle samples generated under downward gravitational acceleration exhibit clear anisotropy in shear strength, thereby proving the hypothesis. When using contact normal‐based and void‐based fabric tensors to quantify fabric anisotropy in the material, we find that the intensity of anisotropy is discernible but low prior to shearing and is dependent on the consolidation process and the dispersity of the sample. The fact that samples with very low anisotropy intensity measurements still exhibit fairly strong strength anisotropy suggests that current typical contact normal‐based and void‐based second‐order fabric tensor formulations may not be very effective in reflecting the anisotropic peak shear strength of granular materials. Copyright © 2017 John Wiley & Sons, Ltd.
Wang, Rui↗
Influence of voids on the strength of wrought materials
Three-dimensional voids, which are present in most materials, may be satisfactorily modelled by two-dimensional holes (i.e., cylindrical voids) in sheet metal. In this study, the influence of certain orientations and shapes of voids upon the mechanical properties and fracture behavior of certain ductile materials has been studied. The presence of voids is found to exert a negligible influence on the ultimate tensile strength, owing to plastic flow neutralizing the stress intensification present before yielding occurs. The shape and orientation of the defects, however, are seen to play an important role relative to strain at fracture. The maximum intensified tensile stress criterion which holds for brittle materials is found to apply to ductile materials as well.
Shaw, M. C.↗
Final Technical Report for DE-SC0008135, Modulating Thermal Transport Phenomena in Nanostructures via Elastic Strain at Extreme Limits of Strength
Nanoscale materials fabricated with nearly pristine crystal structure are often endowed with ultra-strength behavior, where material failure occurs at a significant fraction of its ideal limit. The thermal conductivity exhibited by such materials is also uniquely affected by the high surface-to-volume ratio at the nanoscale. The juxtaposition of the vastly increased dynamic range of elastic strain available in ultra-strength nanomaterials and altered thermal transport shows promise for tunable thermal properties. This project aims to exploit these properties of high-strength nanostructures to elucidate the coupling between large mechanical strains and thermal conductivity (both electron and phonon) leading to better understanding and control of the thermal performance in these materials. Unique fabrication methods to produce nanosized quasi-defect free single crystals and modern nanomechanical testing will be used to identify the size-dependent dynamic range of elastic strain and understand deformation mechanisms near the ideal limit. Identifying and quantifying thermal transport phenomena as a function of mechanical strain in these nanostructures will open the door to using elastic strain engineering in high-strength nanomaterials to tune thermal transport. The results of these investigations will be used to improve the performance, efficiency, and versatility of advanced thermal management and energy conversion devices with tunable response.
36 MATERIALS SCIENCE↗
Surface engineering to enhance heat generation and joint strength in dissimilar materials AZ31 and DP590 ultrasonic welding
A multiscale simulation approach was developed and employed to optimize the sheet surface conditions for higher interfacial temperature and joint strength in ultrasonic welding of magnesium alloy AZ31 and dual-phase steel DP590. First, a mesoscale model was used to study the relationship between friction coefficient and surface roughness, which can be modified by various engineering methods. Then a macroscopic process model was employed to study the effects of surface roughness on heat generation, indicating that a temperature increase can be achieved with rougher surfaces on two sides of both DP590 and AZ31 sheets. Samples prepared by sanding and filing, as well as grinding, were first characterized for surface roughness and then welded under ultrasonic vibration. An infrared camera was used to measure temperatures in situ for model validation. Overall, lap shear test results for the welded joint showed that the joint strength can be improved by 10~25% using filing and round grinding methods as a result of the enhanced heat generation and mechanical interlocking on the interface.
42 ENGINEERING↗
Current and Future Uses of Aluminum in the Automotive Industry
Aluminum use is growing in automotive closures and body in white applications to improve vehicle performance and fuel economy. The auto industry is looking for higher strength aluminum materials needed for strength driven safety critical parts. Through cooperation with industrial partners and support from the Department of Energy (DOE), multiple experimental 7xxx alloys were developed for automotive applications. The objective is to enable complex shapes to be formed at temperatures below 225° C. A demonstration part has been developed that is representative of the forming challenges within a current hot stamped door ring component. This part tooling has been built and installed into a press line which includes blank heating and robotic transfer. Forming trials of these alloys are currently underway and the formability, strength and corrosion performance of these materials are being evaluated.
36 MATERIALS SCIENCE↗
Strength characteristics of composite materials annual report, jan. 1964 - jan. 1965
Strength characteristics of anisotropic and laminated composite materials
COMPOSITE MATERIAL↗
Fatigue Strengths of Aircraft Materials: Axial-Load Fatigue Tests on Edge-Notched Sheet Specimens of 2024-T3 and 7075-T6 Aluminum Alloys and of SAE 4130 Steel with Notch Radii of 0.004 and 0.070 inch
The present report gives results of axial-load fatigue tests on notched specimens of three sheet materials: 2024-T3 and 7075-T6 aluminum alloys and normalized SAE 4130 steel. Two edge-notched specimens were designed and tested, each having a theoretical stress-concentration factor K(sub t) = 4.0. The radii of the notches were 0.004 and 0.070 inch. Tests of these specimens were run at two levels of nominal mean stress: 0 and 20,000 psi. Results of these studies extended information previously reported on tests of specimens with varying notch severity. They afford data on the variation of fatigue-strength reduction with notch radius and on the potential usefulness of Neuber's technical stress-concentration factor K(sub n).
Grover, H. J.↗
Interactions between creep, fatigue and strain aging in two refractory alloys
The application of low-amplitude, high-frequency fatigue vibrations during creep testing of two strain-aging refractory alloys (molybdenum-base TZC and tantalum-base T-111) significantly reduced the creep strength of these materials. This strength reduction caused dramatic increases in both the first stage creep strain and the second stage creep rate. The magnitude of the creep rate acceleration varied directly with both frequency and A ratio (ratio of alternating to mean stress), and also varied with temperature, being greatest in the range where the strain-aging phenomenon was most prominent. It was concluded that the creep rate acceleration resulted from a negative strain rate sensitivity which is associated with the strain aging phenomenon in these materials. (A negative rate sensitivity causes flow stress to decrease with increasing strain rate, instead of increasing as in normal materials). By combining two analytical expressions which are normally used to describe creep and strain aging behavior, an expression was developed which correctly described the influence of temperature, frequency, and A ratio on the TZC creep rate acceleration.
Sheffler, K. D.↗
Interactions between creep, fatigue, and strain-aging in two refractory metal alloys.
The application of low-amplitude, high-frequency fatigue vibrations during creep testing of two strain-aging refractory alloys (molybdenum-base TZC and tantalum-base T-111) significantly reduced the creep strength of these materials. This strength reduction caused dramatic increases in both the first-stage creep strain and the second-stage creep rate. The magnitude of the creep rate acceleration varied directly with both frequency and A ratio (ratio of alternating to mean stress), and also varied with temperature, being greatest in the range where the strain-aging phenomenon was most prominent. It was concluded that the creep rate acceleration resulted from a negative strain rate sensitivity which is associated with the strain-aging phenomenon in these materials. (A negative rate sensitivity causes flow stress to decrease with increasing strain rate, instead of increasing as in normal materials.)
Sheffler, K. D.↗
Predicting the yield strength of a 3D printed porous material from its internal geometry
Not provided.
Engineering↗