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Tensile Strength: The maximum stress a material subjected to a stretching load can withstand without tearing. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed, p2001)

Tests of Hardened Concrete in Tension

JoVE 10423

Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA

In a previous laboratory focused on concrete in compression, we observed that concrete can withstand very large stresses under uniaxial compressive forces. However, the failures observed were not compressive failures but failures along shear planes where maximum tensile forces occur. Thus, it is important to understand the behavior of concrete in tension and particularly its maximum strength as that will govern both its ultimate and service behavior. From the ultimate standpoint, combinations of tension and shear stresses will lead to cracking and immediate and catastrophic failure. For that reason, concrete is seldom if ever used in an unreinforced condition in structural applications; most concrete members will be reinforced with steel so that these cracks can be stopped and the crack widths limited. The latter is important from the serviceability standpoint because controlling crack widths and distribution is the key to durability, as this will impede deicing salts and similar chemicals from penetrating and corroding the reinforcing steel. The objectives of this experiment are threefold: (1) to conduct tensile split cylinder tests to determine concrete tensile strength, (2) to conduct

 Structural Engineering

Stress-Strain Characteristics of Aluminum

JoVE 10362

Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA

Aluminum is one of the most abundant materials in our lives, as it is omnipresent in everything from soda cans to airplane components. Its widespread use is relatively recent (1900AD), primarily because aluminum does not occur in its free state, but rather in combination with oxygen and other elements, often in the form of Al2O3. Aluminum was originally obtained from bauxite mineral deposits in tropical countries, and its refinement requires very high-energy consumption. The high cost of producing quality aluminum is another reason why it is a very widely recycled material. Aluminum, especially when alloyed with one or more of several common elements, has been increasingly used in architectural, transportation, chemical, and electrical applications. Today, aluminum is surpassed only by steel in its use as a structural material. Aluminum is available, like most other metals, as flat-rolled products, extrusions, forgings, and castings. Aluminum offers superior strength-to-weight ratio, corrosion resistance, ease of fabrication, non-magnetic properties, high thermal and electrical conductivity, as well as ease of alloying.

 Structural Engineering

Synthesis of Thermogelling Poly(N-isopropylacrylamide)-graft-chondroitin Sulfate Composites with Alginate Microparticles for Tissue Engineering

1Department of Chemical Engineering, Rowan University, 2Department of Biological Sciences, Rowan University, 3Department of Biomedical Engineering, Drexel University

JoVE 53704


Stress-Strain Characteristics of Steels

JoVE 10361

Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA

The importance of materials to human development is clearly captured by the early classifications of world history into periods such as the Stone Age, Iron Age, and the Bronze Age. The introduction of the Siemens and Bessemer processes to produce steels in the mid-1800s is arguably the single most important development in launching the Industrial Revolution that transformed much of Europe and the USA in the second half of the 19th century from agrarian societies into the urban and mechanized societies of today. Steel, in its almost infinite variations, is all around us, from our kitchen appliances to cars, to lifelines such as electrical transmission networks and water distribution systems. In this experiment we will look at the stress-strain behavior of two types of steel that bound the range usually seen in civil engineering applications - from a very mild, hot rolled steel to a hard, cold rolled one.

 Structural Engineering

Tension Test of Fiber-Reinforced Polymeric Materials

JoVE 10417

Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA

Fiber-reinforced polymeric materials (FRP) are composite materials that are formed by longitudinal fibers embedded in a polymeric resin, thereby creating a polymer matrix with aligned fibers along one or more directions. In its simplest form, the fibers in FRP materials are aligned in an orderly, parallel fashion, thus imparting orthotropic material characteristics, meaning that the material will behave differently in the two directions. Parallel to the fibers, the material will be very strong and/or stiff, whereas perpendicular to the fibers will be very weak, as the strength can only be attributed to the resin instead of the whole matrix. An example of this unidirectional configuration is the commercially available FRP reinforcing bars, which mimic the conventional steel bars used in reinforced concrete construction. FRP materials are used both as stand-alone structures such as pedestrian bridges and staircases, and also as materials to strengthen and repair existing structures. The thin, long plates are often epoxied to existing concrete structures to add strength. In this case, the FRP bars act as external reinforcement. The FRP bars and plates are ligh

 Structural Engineering

Fatigue of Metals

JoVE 10416

Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA

The importance of studying metal fatigue in civil infrastructure projects was brought into the spotlight by the collapse of the Silver Bridge in Point Pleasant, West Virginia in 1967. The eyebar-chain suspension bridge over the Ohio River collapsed during evening rush hour, killing 46 people as a result of the failure of a single eyebar with a small 0.1-inch defect. The defect reached a critical length after repeated loading conditions and failed in a brittle fashion causing the collapse. This event garnered attention in the bridge engineering community and highlighted the importance of testing and monitoring fatigue in metals. Under normal service conditions, a material can be subjected to numerous applications of service (or everyday) loads. These loads are typically at most 30%-40% of the ultimate strength of the structure. However, after the accrual of repeated loadings, at magnitudes substantially below the ultimate strength, a material can experience what is termed fatigue failure. Fatigue failure can occur suddenly and without significant prior deformation and is linked with crack growth and rapid propagation. Fatigue is a complex process, with many factors affecting

 Structural Engineering

Effects of Allogeneic Platelet-Rich Plasma (PRP) on the Healing Process of Sectioned Achilles Tendons of Rats: A Methodological Description

1Experimental Surgery, GIGA-R & Credec, University of Liège, 2Laboratory of Connective Tissues Biology, GIGA-R, University of Liège, 3Department Argenco, University of Liège, 4Department of Clinical Biology, University Hospital of Liège, University of Liège, 5Physical Medicine and Sport Traumatology Department, FIFA Medical Center of Excellence, University Hospital of Liège, University of Liège

JoVE 55759


Rockwell Hardness Test and the Effect of Treatment on Steel

JoVE 10386

Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA

Hardness testing is one of the most universally valuable mechanical tests available to engineers, as it is both simple and relatively inexpensive for the wealth of information and data it produces. Hardness testing, generally in the form of a surface penetration test, is both quicker and less destructive than tensile testing. Hardness provides a linear relationship with tensile strength over a wide range of strengths for many materials, such as steel. Hardness tests are empirical, rather than derived from theory, as the results conflate effects from many different materials properties (Young's modulus, yield strength, etc.). Hardness is a characteristic of a material used to describe how much plastic deformation (yield) that a material will undergo when a known force is applied). One can characterize hardness in three manners: scratch, indentation, and rebound hardness. A common early example of a hardness (scratch) test is the Mohs scale (1820), derived for minerals, and in which talc has a value of 1 and diamond a value of 10. In indentation testing using the Rockwell approach, small indenters are used with different loads. The most common are the Rockwell Hardness B (HRB), which uses

 Structural Engineering

Compression Tests on Hardened Concrete

JoVE 10421

Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA

There are two distinct stages in a construction project involving concrete. The first stage involves batching, transporting, and casting fresh concrete. At this stage, the material is viscous, and the workability and finishability are the key performance criteria. The second stage occurs when the hydration process begins shortly after the concrete is placed in the form, and the concrete will set and begin to harden. This process is very complex, and not all of its phases are well understood and characterized. Nevertheless, the concrete should achieve its intended design strength and stiffness at about 14 to 28 days after casting. At this point, a series of tests will be conducted on concrete cylinders cast at the time of placement to determine the concrete's compressive and tensile strengths, as well as on occasion, its stiffness. The objectives of this experiment are threefold: (1) to conduct compressive cylinder tests to determine the 7-, 14-, and 28-day strength of concrete, (2) to determine the modulus of elasticity at 28 days, and (3) to demonstrate the use of a simple non-destructive test to determine in situ concrete strength.

 Structural Engineering

Adapted Resistance Training Improves Strength in Eight Weeks in Individuals with Multiple Sclerosis

1Motion Analysis Laboratory, Kennedy Krieger Institute, 2Physical Medicine & Rehabilitation, Johns Hopkins University School of Medicine, 3Johns Hopkins University School of Medicine, 4Department of Neurology, Johns Hopkins University School of Medicine

JoVE 53449


Two Methods for Decellularization of Plant Tissues for Tissue Engineering Applications

1Department of Surgery, University of Wisconsin-Madison, 2Department of Orthopedics and Rehabilitation, University of Wisconsin School of Medicine and Public Health, 3Department of Biomedical Engineering, University of Wisconsin College of Engineering, 4Department of Biomedical Engineering, Worcester Polytechnic Institute

JoVE 57586


Surgical Technique for the Implantation of Tissue Engineered Vascular Grafts and Subsequent In Vivo Monitoring

1Department of Physiology & Bio-Physics, State University of New York Buffalo School of Medicine, 2Department of Pediatrics, State University of New York Buffalo School of Medicine, 3Department of Chemical and Biological Engineering, State University of New York Buffalo School of Engineering

JoVE 52354


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