J. Wadsworth, D.R. Lesuer /Materials Characterization 45(2000)289-313 (such as volume percent of the con materials g) was discovered by an excavation team near an Ind layer thickness), and processin ry, LMCs ir passage(Southern side) in the great Pyramid at can be engineered to produce with pre- Gizeh, Egypt. The location of the plate was within scribed properties. an undisturbed section high up on the pyramid In the present paper, Section 2 deals with the The plate was removed to the British Museum and history of laminated composites. In particular, exam- was not examined for its structure until El Gayer ples of their existence, composition, and structure are nd Jones used modern metallographic techniques detailed. Extra emphasis is given to the Japanese on a small (1.7 g) sample from the plate and sword both because of its complexity as a laminate published their findings in 1989[]. A comment at several levels, and its relatively well-documented by Craddock and Lang [3 was included in the history and the technical details tha same issue of the journal story. Included at the end of the section are some The significance of the plate is twofold. First, if it comments on modern knives that duplicate, in part, can be shown to be contemporaneous with the build the ancient weapons. Section 3 first describes modern ing of the pyramid, then it is one of the oldest known engineering applications of LMCs. Scientific and plates of iron metal ever discovered and dates from engineering studies on laminated composites are then the 4th Dynasty, circa 2750 BC. Second, the metallo- presented- in some cases at the very thin-layer graphic study of El Gayer and Jones revealed that the level, and in others at layer thicknesses that were close to those found in ancient laminates. processing methods, as well as strength, durability, toughness and damping properties, are discussed. The mechan- hese laminates have been inexpertly wela ates of wrought iron and isms of ving toughn ness by lamination are de- gether by hammering. The various layers differ scribed in detail om each other in their grain sizes, carbon contents Where possible, the mechanisms leading to im- the nature of their non-metallic inclusions and in proved properties of modern engineered laminated their thicknesses composites are linked back to ancient artifacts It was further deduced from elongated non-metal- lic inclusions that the welding process had been 2. History carried out at modest temperatures( 800 C)allow- ing recrystallization of the iron matrix grains. The The idea of laminating similar or dissimilar metals bsence of metallic copper globules and only small or alloys to form a composite material has been traces of elemental copper suggested that the plate known from antiquity. The motivations for laminat had not been produced as a by-product of copper ing metals are varied. For example, in carburizing the smelting operations of iron-rich copper ores. Also, earliest forms of wrought iron, only thin layers could a chemical analysis reported in 1926 revealed only be carburized and so lamination was a way to create race levels of nickel, thereby confirming the plate ulk material. ( This could be the motivation to be of terrestrial (but not natural) origin rather most ancient laminates Another reason is that the than to be meteoric [2]. (It is noted that the above ard material, steel, was rare and it was expedient to view on lamination is not universally agreed upon sandwich it between more common materials (Thi An alternate view is that the heterogeneous nature motive is found in medieval knives )From a mechan- of te is a direct result of a heterogeneou ical viewpoint, optimizing the combination of starting piece [4]). trength, toughness, and sharpness is the basis for Summarizing, El Gayer and Jones concluded that lamination.(Examples include the Japanese sword, the iron pieces comprising the laminate were the Halberd, and modern laminates. Finally, there is a strong motivation based on decorative appeal .intentionally produced during small-scale(and, Many modern knives are made in laminated form ossibly, very primitive) operations primarily de- for this reason but it could have been a motive in signed for the production of iron metal(rather than ancient knives also. ) Some selected examples of copper metal). Furthermore, the presence of abur laminated materials follow ant inclusions of unreduced (or incompletely oxides in the metal 2.1. Laminated iron plate found at the great Pyramid laminations shows that the'smelting operations had of Gizeh rried out at low temperatures (probably between 1000"C and 1100C)and that the ron had been produced by the direct reduction In 1837, an iron plate (26 cm x 86 cm x a method maximum thickness of 0.4 cm and weighing 750 produced In which no molten iron is normally(such as volume percent of the component materials and layer thickness), and processing history, LMCs can be engineered to produce a material with pre￾scribed properties. In the present paper, Section 2 deals with the history of laminated composites. In particular, exam￾ples of their existence, composition, and structure are detailed. Extra emphasis is given to the Japanese sword both because of its complexity as a laminate at several levels, and its relatively well-documented history and the technical details that accompany that history. Included at the end of the section are some comments on modern knives that duplicate, in part, the ancient weapons. Section 3 first describes modern engineering applications of LMCs. Scientific and engineering studies on laminated composites are then presented Ð in some cases at the very thin-layer level, and in others at layer thicknesses that were close to those found in ancient laminates. Processing methods, as well as strength, durability, toughness, and damping properties, are discussed. The mechan￾isms of improving toughness by lamination are de￾scribed in detail. Where possible, the mechanisms leading to im￾proved properties of modern engineered laminated composites are linked back to ancient artifacts. 2. History The idea of laminating similar or dissimilar metals or alloys to form a composite material has been known from antiquity. The motivations for laminat￾ing metals are varied. For example, in carburizing the earliest forms of wrought iron, only thin layers could be carburized and so lamination was a way to create bulk material. (This could be the motivation for the most ancient laminates.) Another reason is that the hard material, steel, was rare and it was expedient to sandwich it between more common materials. (This motive is found in medieval knives.) From a mechan￾ical viewpoint, optimizing the combination of strength, toughness, and sharpness is the basis for lamination. (Examples include the Japanese sword, the Halberd, and modern laminates.) Finally, there is a strong motivation based on decorative appeal. (Many modern knives are made in laminated form for this reason, but it could have been a motive in ancient knives also.) Some selected examples of laminated materials follow. 2.1. Laminated iron plate found at the Great Pyramid of Gizeh In 1837, an iron plate (26 cm 86 cm a maximum thickness of 0.4 cm and weighing 750 g) was discovered by an excavation team near an air passage (Southern side) in the Great Pyramid at Gizeh, Egypt. The location of the plate was within an undisturbed section high up on the pyramid. The plate was removed to the British Museum and was not examined for its structure until El Gayer and Jones used modern metallographic techniques on a small (1.7 g) sample from the plate and published their findings in 1989 [2]. A comment by Craddock and Lang [3] was included in the same issue of the journal. The significance of the plate is twofold. First, if it can be shown to be contemporaneous with the build￾ing of the pyramid, then it is one of the oldest known plates of iron metal ever discovered and dates from the 4th Dynasty, circa 2750 BC. Second, the metallo￾graphic study of El Gayer and Jones revealed that the plate consists of: ...numerous laminates of wrought iron and that these laminates have been inexpertly welded together by hammering. The various layers differ from each other in their grain sizes, carbon contents, the nature of their non-metallic inclusions, and in their thicknesses. It was further deduced from elongated non-metal￾lic inclusions that the welding process had been carried out at modest temperatures ( 800°C) allow￾ing recrystallization of the iron matrix grains. The absence of metallic copper globules and only small traces of elemental copper suggested that the plate had not been produced as a by-product of copper smelting operations of iron-rich copper ores. Also, a chemical analysis reported in 1926 revealed only trace levels of nickel, thereby confirming the plate to be of terrestrial (but not natural) origin rather than to be meteoric [2]. (It is noted that the above view on lamination is not universally agreed upon. An alternate view is that the heterogeneous nature of the plate is a direct result of a heterogeneous starting piece [4]). Summarizing, El Gayer and Jones concluded that the iron pieces comprising the laminate were: ...intentionally produced during small-scale (and, possibly, very primitive) operations primarily de￾signed for the production of iron metal (rather than copper metal). Furthermore, the presence of abun￾dant inclusions of unreduced (or incompletely reduced) fragments of iron oxides in the metal laminations shows that the `smelting' operations had been inexpertly carried out at low temperatures (probably between 1000°C and 1100°C) and that the iron had been produced by the `direct reduction' method Ð in which no molten iron is normally produced. 290 J. Wadsworth, D.R. Lesuer / Materials Characterization 45 (2000) 289±313