Electricity And Magnetism Section 2 Reinforcement

[Tambra Podrasky]

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Abstract: The demand for additively manufactured polymer composites with increased specific properties and functional microstructure has drastically increased over the past decade. The ability to manufacture complex designs that can maximize strength while reducing weight in an automated fashion has made 3D-printed composites a popular research target in the field of engineering. However, a significant amount of understanding and basic research is still necessary to decode the fundamental process mechanisms of combining enhanced functionality and additively manufactured composites. In this review, external field-assisted additive manufacturing techniques for polymer composites are discussed with respect to (1) self-assembly into complex microstructures, (2) control of fiber orientation for improved interlayer mechanical properties, and (3) incorporation of multi-functionalities such as electrical conductivity, self-healing, sensing, and other functional capabilities. A comparison between reinforcement shapes and the type of external field used to achieve mechanical property improvements in printed composites is addressed. Research has shown the use of such materials in the production of parts exhibiting high strength-to-weight ratio for use in aerospace and automotive fields, sensors for monitoring stress and conducting electricity, and the production of flexible batteries. Keywords: additive manufacturing; field-assisted; tunable properties; fiber orientation control; multifunctional composites; printed composites; microstructure

Roy, Madhuparna, Phong Tran, Tarik Dickens, and Amanda Schrand. 2020. "Composite Reinforcement Architectures: A Review of Field-Assisted Additive Manufacturing for Polymers" Journal of Composites Science 4, no. 1: 1.

Are these produced magnetic and electric field produced due to one defined to be constant or variable?If these are defined to be variable then do they continue to produce one another? By this I mean if changing electric field produces changing magnetic field, does this changing magnetic field produce a new electric field or the same one again?

Ideas like differentiation could help show how electricity and magnetism are related. In fact, physicists actually look at them as a single force called electromagnetism. But, it is important to note that a magnet not moving or changing relative to an electron will not put any force on the electron. Said another way: an unchanging magnetic field will not create or change an electric field. The reverse is also true: an unchanging electric field will not create or change a magnetic field. This change is required both ways at the same time.

Your point is a critical idea in physics, a self sustaining electromagnetic field due to constant change. The idea is explained in Maxwell's equations. The idea is used as the explanation of light, also known as electromagnetic radiation. The idea is also used in the explanation of the earths magnetic field. And in the explanation of the newly developing model of a Polariton. And most likely in many more areas of science.

If you want to know more about electromagnetism, and you already know how differentiation and force fields work, I would recommend starting with Maxwell's equations, then move into understanding Polarization.

It appears people may be upset about the lack or presence of causality in my answer (a comment after a down vote would be nice)... I would like to address this point, and the comment provided, but it has no simple answer.

If I use a magnet in a generator to make electricity the cause is clear. But, then I can use that same motor to do the opposite, generating motion (a changing magnetic field) from electricity. Clearly one is not the cause of the other.

A case for causality could certainly be made for earth's magnetic field and core current... but which one actually did come first the chicken or the egg. Not sure geologists have enough evidence to prove a changing magnetic or changing electric field came first, just knowledge that our magnetic poles swap.

From the case of earth it is clear the question is not easily answerable. In quantum physics the electric field of an electron must have an angular momentum to give it the magnetic field measured in experiments. However, it does not actually spin.

Concrete deterioration and steel corrosion are major concerns to bridge owners and engineers. The corrosion of steel reinforcement in concrete construction impairs the durability and longevity of prestressed concrete girders. Although steel reinforcing compensates for the weakness in tensile strength of the concrete, it is the leading cause of concrete deterioration.

Prestressed concrete is less permeable and has a higher alkalinity than normal concrete. However, steel reinforcement can be corroded in the case of poorly detailed or constructed systems, or when the environment is more severe than expected. The corrosion of the steel strands decreases the ultimate strength and ductility of strand and leads to fracture, and may cause premature failure of concrete structures. Concrete cracks form over prestressed steel strands, permitting water and de-icing chemicals to penetrate to the steel and accelerate corrosion and create delamination and spalling.

In 2002, the Federal Highway Administration, in partnership with NACE International released a benchmark study, Corrosion Costs and Preventive Strategies in the United States (FHWA-RD-01-156), on costs associated with metallic corrosion in a wide range of industries. The report estimated the annual direct costs for replacement and maintenance of bridges in poor condition to be $8.3 billion, but the indirect costs of corrosion incurred by users and owners increase exponentially. The report estimated the indirect costs to the user, such as traffic delays and lost productivity, to be as high as 10 times that of direct corrosion costs. In 2013, NACE International estimated the annual direct cost of corrosion for highway bridges to be $13.6 billion.

Catastrophic collapses have led to a reevaluation of the condition of many bridge structures, which results in bridges being posted for weight restrictions. For instance, on December 27, 2005, the SR1014 Lake View Drive Bridge in Washington, PA, collapsed onto Interstate 70 when one of the prestressed concrete girders failed from dead load. The forensic evaluation of the bridge revealed heavy spalling and corrosion of the strands on the bottom flange of the failed box beam member. Therefore, detecting corrosion in bridges is critical to effective maintenance and repair.

"As such, some NDE data are becoming essential for more effective and economical management of bridges, and concrete bridge decks in particular," says Dr. Joey Hartmann, director of FHWA's Office of Bridges and Structures. "To make more informed decisions addressing safety, reliability, and maintenance of bridge structures, owners have increasingly turned to NDE over the past 15 years to support bridge inspections."

Since the late 1990s, FHWA has conducted several projects on the NDE of steel corrosion embedded in concrete bridges. The magnetic-based methods have been investigated through various projects seeking more efficient and cost-effective corrosion inspections of prestressed concrete girders. Studies have demonstrated that magnetic flux leakage (MFL) systems are an effective NDE means used in the transportation and energy industries to detect corrosion such as loss of general uniform thickness, stress corrosion cracking, and concentrated pitting.

MFL inspection relies on the fact that the gradient of magnetic scalar potential in a magnetized metallic object rises in approaching any loss or added material. The amplitude of the MFL is generally proportional to the magnetization level: the gradient can be significant when the ferromagnetic materials are locally magnetized to full or near saturation. For the purposes of examining prestressed concrete girders, the magnetizer travels the length of the prestressing strands to detect any flux leakage caused by section loss or gain. In other words, the MFL system, in the same manner with leakage from section loss at corrosion, identifies lateral reinforcements (stirrups) from added section at strand-stirrup interfaces.

The magnetic sources can be either permanent or electromagnets. However, permanent magnets have more versatile applications in the field because of their simpler hardware requirements and speedy operation. Sensors are located between two permanent magnet blocks and can pass near the defects to measure the resulting flux leakage field. Sensors can be mounted axially and normally with respect to the direction of the magnetic field, producing a voltage output that changes proportionally with the magnetic field. As concrete is essentially a nonmagnetic material with a relative magnetic permeability of unity, it has negligible influence on the magnetic measurements.

FHWA's NDE Laboratory developed a more effective and field worthy magnetic-based NDE system in 2019 for the detection of steel corrosion in AASHTO-type prestressed concrete girders. The new MFL system is designed by taking computational and analytical measurements using the finite element multiphysics method to size and lay out magnets and determine rare-earth metal strength, select the magnetic field detection sensor, and predict test outputs under corrosion sizes and different concrete steel placements. Sixty-four such sensors are laid out on eight printed circuit boards in 32 pairs along a straight line with a 0.25-inch (0.64-centimeter) spacing. Each pair of sensors represents one channel of data for the normal magnetic field and one channel for the axial field.

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