Test method for measuring strength of a curved sandwich beam

A fixture for testing curved sandwich beams in flexure was designed and evaluated. The test specimen is a continuous sandwich beam consisting of a central circular 90° region connected by two straight legs. The fixture was designed according to the four-point flexure principle to produce a pure bending moment in the curved region. The validity of the test fixture in producing the desired loading was examined by fitting a curved aluminum bar of similar bending stiffness as the sandwich beams considered. Strain gage readings were successfully compared to predictions from curved homogeneous beam theory. In addition, the deflection of the beam at the loading points was analyzed using straight and curved beam theory for the various sections of the beam, and predictions were compared to measured load-displacement response. Good agreement was achieved between experimental and analytical results lending confidence to the test principle. Curved sandwich beams consisting of glass/polyester face sheets over a PVC foam core were tested to failure and the loading response of the beams and their failure behavior are discussed. It was found that the beams failed at the upper face/core interface due to radial tension stress.     

Development of a terrain strength measuring system

An outline of the development of the experimental equipment capable of recording terrain strength tests carried out with a variety of soil probes. The equipment and instrumentation have been designed as a special type of bevameter, because of its capability of parametric soils strength analysis.     

A test apparatus for measuring the biaxial strength of brittle materials

Experimental Techniques -     

材料动态强度直接测量的磁压剪实验技术及应用

提出一种用于直接测量动载荷下材料强度的新方法,即磁驱动压剪联合加载实验技术。从理论和数值计算上分析了压/剪联合作用下材料的应力偏量与屈服强度关系,计算斜波加载下压/剪联合作用时应力偏量与屈服强度的时空演化特性,给出材料强度数值的计算方法。并基于自行研制的强脉冲电流装置和10 T准静态磁场发生器,利用多点双光源外差位移干涉仪(dual laser heterodyne velocimetry, DLHV),开展磁压剪实验对2种铝样品的动态强度进行测量,得到不同加载压力下铝样品的强度。结果表明:磁驱动压/剪联合加载技术为材料的高压强度直接测量提供了一种新途径,是可靠的实验技术。     

Thawing soil strength measurements for predicting vehicle performance

The CRREL Instrumented Vehicle (CIV), shear annulus, direct shear and triaxial compression devices were used to characterize the strength of thawed and thawing soil. Strength was evaluated in terms of the Mohr-Coulomb failure parameters c′ and φ′, which can be used in simple models to predict the tractive performance of vehicles. Use of an instrumented wheel (like those of the CIV) is proposed for terrain strength characterization for traction prediction because the conditions created by a tire slipping on a soil surface are exactly duplicated. The c′ and φ′ values from a portable shear annulus overpredict traction because of the curved nature of the soil failure envelope in the region of low normal stress applied by a portable annulus. Of all the tests, the direct shear test yielded the highest φ′ value, due to its slow deformation rate and drained conditions. The triaxial test produced results closest to those of the instrumented wheel. For all methods, φ′ increases with soil moisture but decreases rapidly beyond the liquid limit of the soil. The φ′ measured with the vehicle was also found to be strongly influenced by the freeze-thaw layering of the soil.     

Nomograms for the estimation of soil strength from indentation tests

The paper presents a selection of graphical techniques for the rapid analysis of the complex non-linear equations describing the penetration performance of drop-indenters in terms of the Mohr-Coulomb strength parameters of a soil. Charts are presented for the evaluation of these parameters from two simple identation measurements. The strength prediction performance of these charts is not particularly good when compared with values obtained off established and more elaborate laboratory methods. However, the attractive feature of the proposed technique is its extreme simplicity and speed of operation. In the solution of many practical soil-machine mechanics problems an order of magnitude estimate of soil strength is usually adequate. It would therefore appear that further refinement of the methods described would be warranted for use in such applications.     

双屈服面法测量金属材料动高压屈服强度的若干改进

在J.R.Asay等提出的双屈服面法（简称AC方法）测量动态屈服强度的基础上,对实验设计和数据处理做了部分改进。在实验设计方面,在满足实验物理设计的前提下,将 AC方法的卸载实验装置(双层飞片和双台阶样品)简化为单飞片和单台阶样品,以简化波系作用,并减少了声速测量不确定度的引入因素。在数据处理方面,发现由Lagrange声速和工程应变关系曲线外推求预冲击态的体积声速容易引入较大的不确定度,而通过Lagrange声速和粒子速度关系曲线可以更清晰地得到塑性卸载起始点,使图解法和积分法得到的屈服强度值趋于一致。利用改进后的AC方法,得到了低温退火后LY12铝在20.0 GPa预冲击压力下的屈服强度为0.6 GPa。     

Evaluation of high-elongation foil strain gages for measuring cyclic plastic strains

The behavior of a certain type of high-elongation foil strain gages (l/32-in. gage length) was checked against the indications of a clip-on extensometer under conditions of cyclic plastic strain (strain range 0.5 percent to 2.8 percent). The gages exhibited limited capability of measuring cyclic plastic strains. Transverse and axial strain measurements by means of the gages enabled determination of Poisson's ratio for elastic and plastic conditions. Results are tabulated and discussed.     

An experimental method of measuring the confined compression strength of geomaterials

Knowledge of the behaviour of geomaterials under confined compression is a pre-requisite for any analysis of their ballistic performance. This study proposes an experimental method of determining the spherical and deviatoric behaviour of these materials under high pressure. Known as the ‘quasi-oedometric compression test’ it consists of compressing a cylindrical specimen tightly enclosed in a thick confinement vessel. The principles of these quasi-oedometric tests are given first, and the steps taken for their execution, together with an examination of the steel used for the confinement vessel. An original way of analysing the data of the test is presented and validated by numerical simulations. These calculations provide valuable information about the influence of the interface product introduced between the vessel and the specimen, and that of friction. Tests are then presented with specimens of aluminium alloy to validate the experimental set-up and the method of analysis. In addition, quasi-oedometric compression tests of cement based material, with and without particles, illustrate the opportunities offered by this testing method, and show that its deviatoric strength and compaction law are significantly improved by ceramic granulates addition.     

Correlation dimension of paddy soil strength in China

Embedding phase space R^m is reconstructed from the spatial series g(x) of cone indices measured in two paddy fields near Nanjing, China. The correlation dimension D₂^m for each field is derived from the correlation integral C^m(r) and the neighbours distance r in log–log scale. Results show D₂^m increases as m, and tends to 5.0, which expresses the estimate of correlation dimension for each soil strength profile measured.     

A piezoelectric stress gauge for measuring dynamic stress in soil and rock media

A piezoelectric stress gauge is described in this paper. Its major performance data are: measuring range 10⁶–10⁸ Pa, response time less than 7μs; non-linearity within ±1% and total stress measurement error within ± 10%. It can be used for measuring dynamic stress in soil, rock and concrete media as well as dynamic force and dynamic pressure in fluids.     

Comparison of soil strength measurements of agricultural soils in Nebraska

In 2014 the University of Nebraska, Lincoln (UNL) was engaged in field testing program to investigate a soil moisture mapping system as a crop management tool. In conjunction with this work, the US Army Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory (ERDC-CRREL) deployed a team to perform soil characterization and strength measurements at three agricultural test sites. The primary objective was an investigation of the Lightweight Deflectometer (LWD) as a soil surface strength tool for the purposes of assessing bearing capacity of soft soils. The LWD measurements were performed with those from more “standard” tests, i.e. the Dynamic Cone Penetrometer, Cone Penetrometer, and Clegg Impact Hammer to determine if the LWD produced results that compared with these methods. The strength test data were also used to calculate California Bearing Ratio (CBR) values using existing equations in order to see if the different test methods produced similar CBR values that could in turn be used to predict the bearing capacity of the sites. The secondary objective was to compare the strength data with the corresponding soil water content data taken by UNL to determine if soil moisture was an indicator of soil strength.     

Fuzzy prediction of soil strength based on water content and composition

Sixteen samples representing various paddy field soils of the main rice-planting regions in South China, with their characteristic values, are listed, by which means the soil strength of any other paddy field soil can be fuzzily predicted when its water content, sand content and clay content are given. Illustrative examples show that the result of prediction seems to be acceptable in engineering practice.     

坝前淤泥土与新填坝体接触面抗剪强度试验研究及工程应用

坝前淤泥面与新填筑坝体接触面是"坝前淤泥面加坝"技术的薄弱环节.为了探究不同工况下淤泥坝基、新填筑坝体,以及淤泥土-新填土接触面的剪切强度特性,以宁夏南部山区西吉县南川水库坝前淤泥面加坝工程为研究对象,通过常规应变式直剪仪、改进常规应变式直剪仪分别进行剪切试验,分析了淤泥土含水率和压实度变化时,淤泥土、新填土、淤泥土-...     

Prestress for maximum strength

The problem of designing prestress to maximize elastic capacity is treated analytically. Our formulation models structures comprised of a one-material elastic continuum, subject to a single deterministic load configuration.The equations needed to predict the optimal prestress design are derived. They are shown to comprise necessary and sufficient conditions for global maximum strength in the unconstrained design problem. The theory is demonstrated on the design of prestress for a thick-walled cylinder.