Experimental mechanics study of a dam Tainter gate

Abstract only availableThe primary objective of this instrumentation project is to determine the performance of the Tainter gate's trunnion bearings at the Carlyle Lake Dam in Illinois. The Tainter gate is a type of radial arm floodgate used in dams and canal locks to control water flow. The trunnion bearings are the critical component of the structure. Friction in the bearing can cause excessive forces in the structural arms of the Tainter gate and can result in a structural failure of the gate Experimental determination of the stresses in the structural arms facilitates computation of friction encountered in the trunnion bearing when raising or lowering the gate. Specially designed transducers which could be readily attached to the structural arm were fabricated and installed to measure the strains present in the gate during routine operation. The transducer consisted of four strain gauges mounted on the flexural transducer and wired in a Wheatstone bridge configuration. The change in resistance of the Wheatstone bridge is linearly related to the strain imposed on the transducer. By measuring the voltage history of the transducer it is possible to determine strain in the structural arms during operations of the Tainter gate. The strains were recorded by using a LabView program custom written for this purpose. Simple mechanics based analysis of the resulting strains is expected to facilitate analysis of forces on the bearing. Preliminary results from the field investigation will be presented and discussed.US Army Corps of Engineers Engineer Research and Development Center, College of Engineering Undergraduate Research Optio

Implementation and validation of a constitutive model for the cyclic behaviour of interface elements

A constitutive model developed for the simulation of the cyclic behaviour of interface elements is proposed. Its theoretical framework is fully based on the plasticity theory. Starting from an existing monotonic model, two new yield surfaces are introduced in order to include non-linear unloading/reloading behaviour in an accurate fashion. The motion of the unloading surfaces is controlled by a mixed hardening law and, by adopting appropriate evolution rules, it is possible to reproduce non-linear behaviour during unloading. Numerical results concerning the analysis of both uniaxial tests and masonry walls are presented and discussed as application and validation examples of the constitutive model

Impact properties of steel fibre reinforced concrete in bending

The effects of strain rate of loading including impact on the bending properties of steel fibre reinforced mortar are studied using an instrumented drop-weight impact machine. Particular emphasis is put on clarifying the influence of the fibre reinforcing parameters and matrix strength. The parameters investigated in the experimental programme include three volume fractions of fibres (1%, 2% and 3%), three fibre aspect ratios (47, 62 and 100, two mortar mixes and four strain rates of loading ranging from 0.5 x 10-5 to 1.2 strains per second. It is found that depending on the fibre reinforcing parameters the energy absorbed by the composite at static loading rates can be one to two orders of magnitude higher than that of the unreinforced matrix. Moreover, up to a three-fold increase is observed in the modulus of rupture and the energy absorbed by the composite when the strain rate increases from 0.5 x 10-5 to 1.2 strain per second.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25071/1/0000502.pd

Quasibrittle fracture scaling and size effect

The report attempts a broad review of the problem of size effect or scaling of failure, which has recently come to the forefront of attention because of its importance for concrete and geotechnical engineering, geomechanics, arctic ice engineering, as well as in designing large loadbearing parts made of advanced ceramics and composites, e.g. for aircraft or ships. First the main results of Weibull statistical theory of random strength are briefly summarized and its applicability and limitations described. In this theory as well as plasticity, elasticity with a strength limit, and linear elastic fracture mechanics (LEFM), the size effect is a simple power law because no characteristic size or length is present. Attention is then focused on the deterministic size effect in quasibrittle materials which, because of the existence of a non-negligible material length characterizing the size of the fracture process zone, represents the bridging between the simple powerlaw size effects of plasticity and of LEFM. The energetic theory of quasibrittle size effect in the bridging region is explained and then a host of recent refinements, extensions and ramifications are discussed. Comments on other types of size effect, including that which might be associated with the fractal geometry of fracture, are also made. The historical development of the size effect theories is outlined and the recent trends of research are emphasized

Quasibrittle fracture scaling and size effect

The report attempts a broad review of the problem of size effect or scaling of failure, which has recently come to the forefront of attention because of its importance for concrete and geotechnical engineering, geomechanics, arctic ice engineering, as well as in designing large loadbearing parts made of advanced ceramics and composites, e.g. for aircraft or ships. First the main results of Weibull statistical theory of random strength are briefly summarized and its applicability and limitations described. In this theory as well as plasticity, elasticity with a strength limit, and linear elastic fracture mechanics (LEFM), the size effect is a simple power law because no characteristic size or length is present. Attention is then focused on the deterministic size effect in quasibrittle materials which, because of the existence of a non-negligible material length characterizing the size of the fracture process zone, represents the bridging between the simple powerlaw size effects of plasticity and of LEFM. The energetic theory of quasibrittle size effect in the bridging region is explained and then a host of recent refinements, extensions and ramifications are discussed. Comments on other types of size effect, including that which might be associated with the fractal geometry of fracture, are also made. The historical development of the size effect theories is outlined and the recent trends of research are emphasized

Distribution of Matrix Cracks in a Uniaxial Ceramic Composite

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65596/1/j.1151-2916.1992.tb08181.x.pd

Photonics and fracture toughness of heterogeneous composite materials

Fracture toughness measures the resistance of a material to fracture. This fundamental property is used in diverse engineering designs including mechanical, civil, materials, electronics and chemical engineering applications. In spite of the advancements made in the past 40 years, the evaluation of this remains challenging for extremely heterogeneous materials such as composite concretes. By taking advantage of the optical properties of a thin birefringent coating on the surface of opaque, notched composite concrete beams, here we sense the evolution of the maximum shear stress distribution on the beams under loading. The location of the maximum deviator stress is tracked ahead of the crack tip on the experimental concrete samples under the ultimate load, and hence the effective crack length is characterised. Using this, the fracture toughness of a number of heterogeneous composite beams is evaluated and the results compare favourably well with other conventional methods using combined experimental and numerical/analytical approaches. Finally a new model, correlating the optically measured shear stress concentration factor and flexural strength with the fracture toughness of concretes is proposed. The current photonics-based study could be vital in evaluating the fracture toughness of even opaque and complex heterogeneous materials more effectively in future

Strength-based and fracture-based approaches in the analysis of fibre debonding

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43037/1/10855_2004_Article_BF00721868.pd