Material Strength Evaluation Research Articles

Toward an ultra-high resolution phased-array system for 3D ultrasonic imaging of solids

Ultrasonic phased-array (PA) systems have been widely adopted in the field of nondestructive evaluation for material characterization and imaging of internal defects. Whereas many defects exhibit complex three-dimensional structures, most PA systems provide only two-dimensional images. In this Letter, we demonstrate the ability to create high-resolution 3D images of internal defects using a PA system based on a piezoelectric and laser ultrasonic system (PLUS). The PLUS combines a piezoelectric transmitter to insonify the structure to be inspected with a laser Doppler vibrometer to create a matrix array of receiver points without contact. The small size of the laser beam results in an ultra-multiple number of elements on the order of thousands, which is impossible to achieve with a conventional piezoelectric matrix array transducer. An emission from a piezoelectric transmitter compensates for the intrinsically low sensitivity of a laser Doppler vibrometer. After formulating the 3D imaging algorithm of the PLUS, we demonstrate that the PLUS with 4096 receiving points (i.e., 64 × 64 points) achieves high-resolution 3D imaging in a specimen with a flat bottom hole. We also visualize the complex structure of stress corrosion cracking. We believe that the 3D imaging capability of the PLUS may open up new avenues to the accurate evaluation of material strength, the identification of the types of defects, and the elucidation of the mechanisms of defect initiation.

Stiffness and flexural strength evaluation of cement stabilized PET blends with demolition wastes

This study was conducted to assess the performance of cement stabilized polyethylene terephthalate (PET) blends with construction and demolition (C&D) waste, namely recycled concrete aggregate (RCA) and crushed brick (CB), as a pavement construction material. A suite of basic characterization tests was undertaken on 3% and 5% PET blends (by mass) with RCA and CB stabilized with 3% cement. The material strength evaluation of the PET blends were undertaken using unconfined compressive strength (UCS) test and the secant modulus results of the blends were also analyzed. Moreover, the resilient moduli (MR) characteristics were evaluated by repeated load triaxial (RLT) test while the flexural strength and the fatigue life of the blends were evaluated by flexural beam tests. UCS results of the cement stabilized PET blends of RCA and CB satisfied the minimum requirement for 7 days of curing samples. Adding PET decreased the MR values of the C&D waste materials, whilst CB showed higher MR values than RCA. PET blends with CB showed high flexural modulus and fatigue life than PET blends with RCA. The cement-stabilized blends of 5% PET with RCA and CB were found to have physical and strength properties which comply with road authority requirements for pavement base/subbase construction.

Report on "The 54<sup>th</sup> Workshop on X-ray Studies on Mechanical Behavior of Materials - Progress of material strength evaluation method using various quantum beams and development to industry -"

Report on "The 54<sup>th</sup> Workshop on X-ray Studies on Mechanical Behavior of Materials - Progress of material strength evaluation method using various quantum beams and development to industry -"

Load Testing of GFRP Composite U-Shape Footbridge

The paper presents the scope of load tests carried out on an innovative shell composite footbridge. The tested footbridge was manufactured in one production cycle and has no components made from materials other than GFRP laminates and PET foam. The load tests, performed on a 14-m long structure, were the final stage of a research program in the Fobridge project carried out in cooperation with: Gdańsk University of Technology (leader), Military University of Technology in Warsaw, and ROMA Co. Ltd.; and co-financed by NCBR. The aim of the tests was to confirm whether the complex U-shape sandwich structure behaves correctly. The design and technological processes involved in constructing this innovative footbridge required the solving of many problems: absence of standards for design of composite footbridges, lack of standardized material data, lack of guidelines for calculation and evaluation of material strength, and no guidelines for infusion of large, thick sandwich elements. Obtaining answers during the design process demanded extensive experimental tests, development of material models, validation of models, updating parameters and extensive numerical parametric studies. The technological aspects of infusion were tested in numerous trials involving the selection of material parameters and control of the infusion parameters. All scientific validation tests were successfully completed and market assessment showed that the proposed product has potential applications; it can be used for overcoming obstacles in rural areas and cities, as well as in regions affected by natural disasters. Load testing included static and dynamic tests. During the former, the span was examined at 117 independent measurement points. The footbridge was loaded with concrete slabs in different configurations. Their total weight ranged from 140 kN up to 202 kN. The applied load at the most heavily loaded structural points caused an effect from 89% to 120%, compared to the load specified by standards (5 kN/m2). Dynamic tests included standard actions (walking, running, synchronous jumps) as well as aggressive tests, all designed to confirm the usability of the footbridge. The performed trials allowed the identification of the modal and damping parameters of the structure. The designated first natural frequency with a value of 7.8 Hz confirmed the correctness of the U-shape cross-section design due to its significant structural rigidity.

Numerical Approach towards Aging Management of Concrete Structures: Material Strength Evaluation in a Massive Concrete Structure under One-Sided Heating

For the purpose of performance evaluation of an existing reinforced concrete member, a computational simulation model to predict the spatial and temporal changes of physical properties of concrete in the member, named the “Computational Cement-Based Material Model (CCBM)”, was proposed. This proposed simulation model includes models of rate of hydration of cement minerals, phase composition, and resultant hygro-thermo-mechanical properties of cement paste (i.e., compressive strength, Young’s modulus, Poisson’s ratio, thermal expansion coefficient, autogenous shrinkage, drying shrinkage, heat capacity, heat transfer coefficient, water vapor sorption isotherms, and water transfer coefficient). Furthermore, the model for compressive strength of concrete considered the variation in cement paste strength due to its colloidal features as well as micro-defects produced around aggregate due to differences in volume between aggregates and mortar upon heating and drying. The concrete properties of spatial distribution and temporal changes were evaluated by coupling these models with heat and water transport. Validation of these models was achieved by using existing experimental data. Using this CCBM, a thick concrete wall made with moderate Portland cement with a water-to-cement ratio of 0.55 under one-sided heating was simulated and potential problems that can arise during an integrity evaluation were discussed. If the required compressive strength, which was assessed within 91 days of placement, remains unchanged, an additional hydration process can build an adequate strength margin to overcome the risk of strength reduction due to heat and drying. However, in the case that the required strength is increased due to a re-evaluated risk, such as the magnitude of an earthquake, performance evaluation is not trivial as the core sample taken from the side where the execution of sampling is possible could exhibit a greater strength than the average strength of the target concrete member. Therefore, numerical evaluation might aid in this kind of situation.

Richtmyer–Meshkov instability as a tool for evaluating material strength under extreme conditions

A new method for the experimental evaluation of material strength of solids under high pressures is proposed. The technique is based on inferring the solid yield strength from induced Richtmyer–Meshkov instabilities by a single steady shock wave. Although the method is limited to loadings below the melting pressure, it still allows to access to an important regime of interest for applied and basic physics with relatively modest facilities widely available. It is envisaged as an alternative in the range of 100 GPa loading pressures to the currently used Rayleigh–Taylor based technique.

Nondestructive evaluation of material strength using depth-sensing indentation

Successful application of any structural repair or strengthening method requires knowledge of strength and stiffness properties of the materials used in the construction. Depth-sensing indentation is a relatively new material testing method that significantly expands the capabilities of conventional hardness tests. Due to the mathematical complexity of the indentation problem, an analytical solution of the load–penetration depth ( P – h ) behavior is not available for most indenters. This study derives the P – h equations for a truncated cone indenter with arbitrary tip radius and included angle, which covers a wide range of geometries including the cylinder and the cone. A step by step procedure for material strength evaluation is introduced and validated using recorded indentation data. The analytical approach described in this paper can be used in evaluating the modulus of elasticity, stiffness and hardness of common construction materials without resorting to empirical equations.

W2 光MEMS開発の現状と材料力学的評価技術の必要性(技術ワークショップ『MEMS開発の最新動向と材料力学への期待』)

W2 光MEMS開発の現状と材料力学的評価技術の必要性(技術ワークショップ『MEMS開発の最新動向と材料力学への期待』)

硬さ試験あれこれ

Hardness is defined as a scale to evaluate the resistance of an object against the force of an impression. Throughout their long history, hardness tests have acquired more and more applications in line with growing attention to the mechanical properties of industrial materials. The more advanced the materials, the greater accuracy is required when testing their hardness, attracting attention to a broader range of parameters which includes the geometry of indenters, loading conditions, and methods for measuring impressions.The purposes of hardness tests have also expanded to include the evaluation of material strength and microstructural changes as a factor of hardness and to guarantee product quality.The level of quality control required for hardness testing machines is highly dependent on their applications. Given this complicated situations, this paper deals with some basics for effectively using the scale of hardness.

不確定性と設計技術

To secure integrity of industrial product, various uncertainties surrounding the design technology must be treated properly. To do this, the uncertainties underlying during the following phases: evaluation of loads, modeling technique of systems of interest, evaluation of material strength, maintenance and inspection and so on, have to be clarified and effective measures to grasp the degree of the uncertainty and to reduce the inherent uncertainty have to be established.The present paper shows the classification of the uncertainties and the fundamental relation with the design technology, and mentions a reliability design method based on probabilistic and statistical techniques, which has been getting popular in many engineering fields, and finally raises some future problems of design methods from the viewpoint of the uncertainties.

Material Strength Evaluation and Damage Detection by X-Ray Diffraction

AbstractThe number of products that have to be inspected in pre-service and/or in service is increasing. Not only inspection for flaws are required increasingly, using the ordinary non-destructive testing, but also inspection of material characteristics, such as material strength evaluation and/or damage detection. For such inspection, X-ray diffraction has great possibilities as one of the most promising techniques, because it is (a) noncontact, (b) very sensitive to changes in parameters of the crystalline structure, and (c) suitable for surface observation.In this paper, three topics are introduced which will be useful in the field of material strength evaluation and damage detection using X-ray diffraction.

最近のＸ線応力測定技術 Ｖ Ｘ線回折法による材料強度評価と損傷検出

最近のＸ線応力測定技術 Ｖ Ｘ線回折法による材料強度評価と損傷検出