Alan W. Pense

Iron through the ages

Abstract A range of iron artifacts, covering an approximate time period from 1000 BCE to 1000 CE, have been metallographically examined. It is concluded that there was little change in iron manufacturing over this time span of 2000 years. It is also concluded that some artifacts, specifically tool and weapon blades, showed that knowledge existed, by at least 500 BCE, to increase hardness both by increasing carbon content and by rapid cooling from the austenite range. The study indicates that there was a considerable degree of sophistication on the part of these early ironworkers, although the processing is thought to have been empirical.

The decline and fall of the roman denarius

The basic silver coin of the early Roman Empire was the denarius. By decree of Caesar Augustus in 15 B.C.E., it was nearly pure silver, 95%-98%, and had a fixed weight and value in relationship to the rest of the Roman monetary system. Over the next 270 years, the silver content of the denarius declined gradually and then precipitously to about 2%. This degradation occurred more rapidly in the provinces than in Rome. The microstructures of a series of Roman denarii taken from this time period are used to illustrate these changes. The final stage of the denarius was a duplex plated coin with a nearly copper core and a silver surface. This produced a lower-cost coin with an apparent value equal to the previous ones. Eventually, the surface coating was so thin that it quickly rubbed off after the coin left the mint. By this time (280 C.E.), the silver coinage of the empire had almost totally lost its value and had to be reconstituted by Diocletion. Among the coins studied is an early duplex plated denarius of Caesar Augustus, probably an early forgery produced during his lifetime in clear violation of his edict.

Effect of Corrosion on Crack Development and Fatigue Life

Fatigue and fracture as well as loss of section caused by corrosion are time-dependent performance characteristics that have the potential to jeopardize the integrity of bridge structures. During the past 25 years these conditions have developed in a number of bridges, resulting in loss of service, costly repairs, and concern about the safety of these structures. A review of the experience with such time-dependent damage since 1970 is presented. The experience is grouped into three categories: fatigue cracking resulting from changes in structural behavior as a result of corrosion, fatigue cracking resulting from development of corrosion notches in members, and stress corrosion of high-strength steel and weld metal. The examples cited illustrate the role of corrosion phenomena in bridge service and the need to control the corrosion conditions on bridge structures.

Microstructural development in the coarse-grained, heat-affected zone in titanium-vanadium microalloyed HSLA steels

Abstract The development of the microstructure in the coarse-grained, heat-affected zone (CGHAZ) of two medium-strength Ti-V microalloyed steels was examined. Single-pass welding of 19mm-thick plates at 5.5kJ/mm resulted in a smaller austenite grain size and a correspondingly narrower CGHAZ in the low-Ti, high-V steel than in the high-Ti, low-V steel. The observed effect is correlated to the differing stability of microalloy precipitates, TiN/TiCN in the high-Ti, low-V steel and TiVN/TiVCN in the low-Ti, high-V steel, and their differing size distributions in the normalized starting materials. The formation of large TiN inclusions reduces the level of Ti and N available to form fine particle dispersions and may, in part, account for the observed austenite grain growth in the high-Ti, low-V steel.

Welding failure analysis

Abstract The failure of welded connections may result from a number of causes; however, they can normally be related to problems in five categories: weld geometrical design, weld process parameters, material-process incompatibilities, weld process execution, and unanticipated service requirements. These problems are sometimes found in combination, and a problem in one of these categories may result in a related problem in another. The normal techniques for determining the cause of a weld joint failure are visual examination, light microscopy, and nondestructive examination, often followed by materials testing, additional sampling, and analytical studies of stress. Electron microscopy may be used to supplement light microscopy. The nondestructive testing and stress analysis are used to provide a global characterization of the joint or structure, while microscopy and chemical analysis provide a more in-depth interpretation of areas that have failed. Forty-five failure analyses of large steel structure are summarized with respect to both the causes of weld failure and the analysis methods used. The most common causes of weld failure for all structures were the execution of the weld and base material weld-process incompatibilities. The original geometric design of the weld and specifications of original welding parameters were important but lesser causes. Most of the weld failure studies used a variety of analysis tools. All used visual inspection with most using light microscopy, chemical analysis, mechanical property determination, nondestructive testing, and stress state studies as part of the analysis. Less than 30% used electron microscopy in the failure cause determination.

Fracture Toughness of Cryogenic Alloys

Nickel alloy steels have been used for many years to contain liquids and gases in the cryogenic and near-cryogenic temperature range. With the advent of large liquefied natural gas (LNG) storage facilities and tankers, renewed attention has been focused on these application of these steels to cryogenic service. The use of ferritic steels in the applications involves not only developing steels with properties in the heavier sections that have not been widely used before, but also producing steels with properties in the heavy section weldments that are compatible with those of the plate. Austenitic materials may also be used, but their lower yield strength and higher cost have limited their application to special designs requiring minimum thickness. The attractiveness of their light weight and corrosion resistance has focused interest on aluminum alloys for cryogenic service.

Analysis of preservice cracking in a large bridge structure

Abstract The failure of a structure to perform its intended purpose is normally detected after some period of service, but sometimes cracking or other difficulties are discovered during preservice inspection. This is illustrated in the cracking discovered in the Luling Bridge, a cable-stayed box-girder structure located near New Orleans, Louisiana, prior to its opening. Visual inspection of the box members indicated cracking in a variety of welded connections. An extensive investigation using polished and etched core samples subsequently identified the two main causes for the cracking phenomena: fatigue cracking from cyclic stresses during shipment, and cracking associated with weld discontinuities. Based on this information, hole drilling to remove existing and potential defects was determined to be an adequate remedial action and allowed the bridge to enter its intended service with minimal delay.