Robert O Ritchie

Robert O Ritchie
University of California, Berkeley | UCB · Department of Materials Science and Engineering

MA, PhD, ScD, FREng, FRS
Focusing on the deformation and fracture of engineering and biological materials, with emphasis on high-entropy alloys.

About

1,012
Publications
345,354
Reads
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64,477
Citations
Introduction
Ritchie's research focuses on the mechanical behavior of engineering & biological materials at multiple length-scales, with emphasis on mechanistic understanding at nano to micro scales & fracture mechanics/fatigue analysis at micro to macro scales. His current interests are in developing lightweight bio-inspired materials with exceptional toughness, high-temperature behavior of ceramic-matrix composites, damage-tolerance in bulk-metallic glasses & high-entropy alloys and fracture in human bone.
Additional affiliations
January 2016 - September 2018
The Hong Kong Polytechnic University
Position
  • Consultant
March 2009 - December 2015
The Hong Kong Polytechnic University
Position
  • Departmental Academic Advisor
July 2005 - June 2011
University of California, Berkeley
Position
  • Chair, Department of Materials Science and Engineering
Education
May 1973 - May 1990
University of Cambridge
Field of study
  • Materials Science
May 1969 - May 1973
University of Cambridge
Field of study
  • Materials Science
May 1969 - May 1972
University of Cambridge
Field of study
  • Materials Science

Publications

Publications (1,012)
Article
High-cycle fatigue (HCF), involving the premature initiation and/or rapid propagation of small cracks to failure due to high-frequency cyclic loading, has been identified as one of the leading causes of turbine engine failures in aircraft. In this work, we consider the feasibility of using grain-boundary engineering to improve the HCF properties of...
Article
The characterization of critical levels of microstructural damage that can lead to fatigue-crack propagation under high-cycle fatigue loading conditions is a major concern for the aircraft industry with respect to the structural integrity of turbine engine components. The extremely high cyclic frequencies characteristic of in-flight loading spectra...
Article
Technologically important mechanical properties of engineering materials often degrade at low temperatures. One class of materials that defy this trend are CrCoNi-based medium- and high-entropy alloys, as they display enhanced strength, ductility, and toughness with decreasing temperature. Here we show, using in situ straining in the transmission e...
Article
An experimental study is described on the fracture toughness and micro-mechanisms associated with the initiation and propagation of cracks in metallic nickel containing marked gradients in grain size, ranging from ∼30 nm to ∼4 μm. Specifically, cracks are grown in a gradient structured (GS) nickel with grain-size gradient ranging from the coarse ma...
Book
Full-text available
An introduction to fracture mechanics that is ideal for faculty, students and practicing engineers KEY FEATURES • Presents how, for a given material, a fracture toughness value can be measured on a small laboratory sample and then used directly to predict the failure (by fracture, fatigue, creep, etc.) of a much larger structure in service • Covers...
Article
It is of particular interest to achieve high elastic recoverable strain in the electrical contact materials while maintaining good electrical conductivity and decent tensile strength. It remains a challenge, especially for bulk-sized metallic materials, as the electrical conductivity and elastic strain limit (or tensile strength) are often mutually...
Article
Structural materials are critical components for our daily lives and industries. This Comment highlights the emerging concepts in structural materials over the past two decades, particularly the multi-principal element alloys, heterostructured materials and additive manufacturing that enables the fabrication of complex architectures.
Article
Full-text available
Electronic waste carries energetic costs and an environmental burden rivaling that of plastic waste due to the rarity and toxicity of the heavy metal components. We introduce recyclable conductive composites for printed circuits formulated with polycaprolactone (PCL), conductive fillers, and enzyme/protectant nanoclusters. Circuits can be printed w...
Preprint
Bioinspired nacre-like structures are effective in toughening materials, yet are difficult to construct in Mg-ceramic systems. Here, a set of Mg-MAX phase composites with nacre-like lamellar and brick-and-mortar architectures were fabricated by pressureless infiltration of the Mg melt into ice-templated ceramic scaffolds. The structure and mechanic...
Article
Unidirectionally oriented architectures demonstrate a notable efficiency in enhancing the properties of macro-porous materials, yet are difficult to construct in a time- and cost-effective fashion. Here a facile approach was exploited for fabricating oriented macro-porous ceramic materials by employing natural graphite flakes as a fugitive material...
Article
Full-text available
Bioinspired architectures are effective in enhancing the mechanical properties of materials, yet are difficult to construct in metallic systems. The structure-property relationships of bioinspired metallic composites also remain unclear. Here, Mg-Ti composites were fabricated by pressureless infiltrating pure Mg melt into three-dimensional (3-D) pr...
Article
Full-text available
High-entropy alloys (HEAs), although often presumed to be random solid solutions, have recently been shown to display nanometer-scale variations in the arrangements of their multiple chemical elements. Here, we study the effects of this compositional heterogeneity in HEAs on their mechanical properties using in situ compression testing in the trans...
Article
We address the three main points of Guo et al . They claim that we should have used the engineering stress versus engineering strain curves to infer the mechanical properties of our nanotwinned titanium, question our sample design on the basis of a finite-element analysis, and doubt the immobility of some preexisting grain/twin boundaries in our el...
Preprint
Full-text available
Medium- and high-entropy alloys based on the CrCoNi-system have been shown to display outstanding strength, tensile ductility and fracture toughness (damage-tolerance properties), especially at cryogenic temperatures. Here we examine the JIc and (back-calculated) KJIc fracture toughness values of the face-centered cubic, equiatomic CrCoNi and CrMnF...
Preprint
Full-text available
Corrosion is a ubiquitous failure mode of materials in extreme environments. The more localized it is, the more difficult it is to detect and more deleterious its effects. Often, the progression of localized corrosion is accompanied by the evolution of porosity in materials, creating internal void-structures that facilitate the ingress of the exter...
Preprint
Dislocation activities play an important role in mediating plastic deformation, even in metals that are prone to deformation twinning. Combining multi-scale and in situ electron microscope characterizations, here we report a discovery of a unique type of dislocation sources that are particularly fertile in low stacking-fault energy materials, inclu...
Article
In this work, the corrosion behavior of Mg-SiO2 nanocomposites, fabricated by powder metallurgy coupled with hybrid microwave sintering and subsequent hot extrusion, was investigated using electrochemical, hydrogen evolution and weight loss measurements. Localized intergranular corrosion behavior was analyzed based on microstructural characteristic...
Article
Full-text available
Since the concept of high-entropy alloys (HEAs) as materials with at least four or five principal elements in (near)-equiatomic composition was introduced in 2004, this new class of materials has penetrated essentially all materials science-related fields. The main reason for this is that some face-centered-cubic alloy compositions have been shown...
Article
Full-text available
The year 2004 marked the beginning of a new era in the design of metallic materials, as the concept of multiple principal component alloys, commonly known as High-Entropy Alloys (HEAs), was proposed by Cantor and Yeh. The unexpected single-phase microstructure, instead of the expected brittle intermetallic compounds, was attributed to the large ent...
Article
Temperature is known to affect deformation mechanisms in metallic alloys. As temperature decreases, the stacking-fault energy in many face-centered cubic (fcc) alloys decreases, resulting in a change of deformation mode from dislocation slip to deformation twinning. Such an impact of temperature can be more complex in compositionally heterogeneous...
Article
Natural silk fibre can reinforce polymer matrix composites for improved toughness and impact strength. However, the optimum selection of matrices for the mechanical performance of silk fibre reinforced plastics (SFRPs) is still unclear, especially with respect to toughness. Here Bombyx mori silk is applied to reinforce three epoxy resin matrices wi...
Article
High-carbon chromium martensite steels are commonly selected for bearing components in the power generation, automotive and aerospace industries where fatigue failure is a major concern. Accordingly, it is of importance to elucidate the structure-property relationships governing the fatigue properties of such bearing steels. Here, the role of micro...
Article
Full-text available
Progress toward developing metal implants as permanent hard‐tissue substitutes requires both osteointegration to achieve load‐bearing support, and energy‐dissipation to prevent overload‐induced bone resorption. However, in existing implants these two properties can only be achieved separately. Optimized by natural evolution, tooth‐periodontal‐ligam...
Article
Studies have established associations between environmental and occupational manganese (Mn) exposure and executive and motor function deficits in children, adolescents, and adults. These health risks from elevated Mn exposure underscore the need for effective exposure biomarkers to improve exposure classification and help detect/diagnose Mn-related...
Article
Fatigue resistance is invariably critical for structural materials, but is rarely considered in the development of new bioinspired materials. Here the fatigue behavior and damage mechanisms of a nacre-like ceramic (yttria-stabilized zirconia) - polymer (polymethyl methacrylate) composite, which resembles human tooth enamel in its stiffness and hard...
Article
Nanostructured metals are usually strong because the ultrahigh density of internal boundaries restricts the mean free path of dislocations. Usually, they are also more brittle because of their diminished work-hardening ability. Nanotwinned materials, with coherent interfaces of mirror symmetry, can overcome this inherent trade-off. We show a bulk n...
Article
Nature-inspired gradients can be implemented in metallic materials to achieve a synergy of strength and ductility. However, due to the small (often microscale) size of the gradient structured samples, their fracture properties have remained relatively unexplored. By fabricating centimeter-sized gradient-structured pure nickel samples using direct-c...
Article
Full-text available
Refractory high-entropy alloys (RHEAs) are designed for high elevated-temperature strength, with both edge and screw dislocations playing an important role for plastic deformation. However, they can also display a significant energetic driving force for chemical short-range ordering (SRO). Here, we investigate mechanisms underlying the mobilities o...
Article
Brittle materials, such as oxide glasses, are usually very sensitive to flaws, giving rise to a macroscopic fracture strength that is much lower than that predicted by theory. The same applies to bulk-metallic glasses (BMGs), with the important difference that these glasses can exhibit certain plastic strain prior to catastrophic failure. Here we c...
Article
Full-text available
Natural fish scales demonstrate outstanding mechanical efficiency owing to their elaborate architectures and thereby may serve as ideal prototypes for the architectural design of man-made materials. Here bioinspired magnesium composites with fish-scale-like orthogonal plywood and double-Bouligand architectures were developed by pressureless infiltr...
Article
Dual-phase mechanical metamaterials, fabricated as a hybrid of two architected lattice materials with different mechanical properties and bioinspired pattering, have been shown to exhibit improved combination of properties, such as enhanced reinforced strength and toughness. In this study, we specifically examine the selection of the reinforcement...
Article
It has been said that “God invented plasticity, but the Devil invented fracture!” Both mechanisms represent the two prime modes of structural failure, respectively plastic collapse and the rupture/breaking of a component, but the concept of developing materials with enhanced resistance to fracture can be difficult. This is because fracture resistan...
Article
The microscopic Bouligand-type architectures of fish scales demonstrate a notable efficiency in enhancing the damage tolerance of materials; nevertheless, it is challenging to reproduce in metals. Here bioinspired tungsten-copper composites with different Bouligand-type architectures mimicking fish scales were fabricated by infiltrating a copper me...
Article
Full-text available
In situ synchrotron X-ray computed micro-tomography and digital volume correlation (DVC) were utilised to understand the failure mechanisms at room temperature and 1050 °C of two NextelTM720/alumina oxide-oxide ceramic-matrix composites (CMCs), termed materials A and B, sintered respectively at 1200 °C and ∼1250 °C. At both test temperatures, three...
Article
This work intends to manipulate the internal flow units in Zr55Cu30Ni5Al10 bulk-metallic glasses (BMGs) through plasma-assisted hydrogenation to generate a positive microalloying effect on plasticity. Based on the cooperative shear model theory, serration-flow statistics during nanoindentation loading and creep tests during the holding stage were u...
Article
The scales of pine cones undergo reversible deformation due to hydration changes in order to optimize seed dispersal. This improves the survivability of the pine. The reversible flexing of the scales is caused by two tissue layers arranged in a sandwich configuration: a layer composed of sclereid cells and a sclerenchyma layer. They expand differen...
Article
Silk fibres exhibit good biodegradability, biocompatibility and balanced strength and toughness, which are useful for toughness/impact-critical composites in the biomedical field. However, the impact of hydration hasn't been studied for silk fibre-reinforced polymers (SFRPs). In this work, SFRPs fabricated via vacuum assisted resin transfer mouldin...
Article
Full-text available
Successfully interfacing enzymes and biomachinery with polymers affords on-demand modification and/or programmable degradation during the manufacture, utilization and disposal of plastics, but requires controlled biocatalysis in solid matrices with macromolecular substrates1–7. Embedding enzyme microparticles speeds up polyester degradation, but co...
Article
Full-text available
Additive manufacturing of industrially-relevant high-performance parts and products is today a reality, especially for metal additive manufacturing technologies. The design complexity that is now possible makes it particularly useful to improve product performance in a variety of applications. Metal additive manufacturing is especially well matured...
Article
Significance High-entropy alloys, an exciting new class of structural materials involving many concentrated elements, are generally assumed to be chemically disordered. This work reveals how magnetic interactions can drive atomic-scale ordering in a mechanically interesting system that has been widely studied as a model for many promising alloys. T...
Article
The presence, nature, and impact of chemical short-range order in the multi-principal element alloy CrCoNi are all topics of current interest and debate. First-principles calculations reveal that its origins are fundamentally magnetic, involving repulsion between like-spin Co-Cr and Cr-Cr pairs that is complemented by the formation of a magneticall...
Article
Hydrogen-accelerated fatigue crack growth is a most severe manifestation of hydrogen embrittlement. A mechanistic and predictive model is still lacking partly due to the lack of a descriptive constitutive model of the hydrogen/material interaction at the macroscale under cyclic loading. Such a model could be used to assess the nature of the stress...
Article
For composite materials applied for energy absorption and vibration/noise reduction, it is of particular significance to clarify the role of strain rate and temperature on their mechanical properties. Here we present a study on the effects of strain rate (from 10⁻³ s⁻¹ to 1 s⁻¹) and temperature (from room temperature to 350 °C) on the compressive p...
Article
Full-text available
A widely used schematic picture of the potential energy landscape (PEL) for liquid and glass gives an impression that the pathway of moving from a valley to another through a saddle point is predetermined. However, in reality the pathway is much more stochastic and unpredictable because thermal history is wiped out at the saddle point and the pathw...
Article
The deformation and fracture of a 0/90 °Nextel 720 alumina/Mullite fibre / alumina matrix ceramic-matrix composite material has been observed by in situ synchrotron x-ray computed micro-tomography at ambient temperature and at 1100 °C. A three-point loading configuration was used and samples were loaded monotonically until final fracture. The flexu...
Article
Nature's materials are generally hybrid composites with superior mechanical properties achieved through delicate architectural designs. Inspired by the precipitation hardening mechanisms observed in biological materials as well as engineering alloys, we develop here dual-phase mechanical metamaterial composites by employing architected lattice mate...
Article
Full-text available
Ever-harsher service conditions in the future will call for materials with increasing ability to undergo deformation without sustaining damage while retaining high strength. Prime candidates for these conditions are certain high-entropy alloys (HEAs), which have extraordinary work-hardening ability and toughness. By subjecting the equiatomic CrMnFe...
Article
Full-text available
Ever-harsher service conditions in the future will call for materials with increasing ability to undergo deformation without sustaining damage while retaining high strength. Prime candidates for these conditions are certain high-entropy alloys (HEAs), which have extraordinary work-hardening ability and toughness. By subjecting the equiatomic CrMnFe...
Article
Full-text available
Bone continuously adapts to its mechanical environment by structural reorganization to maintain mechanical strength. As the adaptive capabilities of bone are portrayed in its nano- and microstructure, the existence of dark and bright osteons with contrasting preferential collagen fiber orientation (longitudinal and oblique-angled, respectively) poi...
Article
Full-text available
Heterostructured materials are an emerging class of materials with superior performances that are unattainable by their conventional homogeneous counterparts. They consist of heterogeneous zones with dramatic (>100%) variations in mechanical and/or physical properties. The interaction in these hetero-zones produces a synergistic effect where the in...
Article
Full-text available
Hydrogen-accelerated fatigue crack growth is a most severe manifestation of hydrogen embrittlement. A mechanistic and predictive model is still lacking partly due to the lack of a descriptive constitutive model of the hydrogen/material interaction at the macroscale under cyclic loading. Such a model could be used to assess the nature of the stress...
Article
Brittle materials, such as oxide glasses, are usually very sensitive to flaws, giving rise to a macroscopic fracture strength that is much lower than that predicted by theory. The same applies to bulk-metallic glasses (BMGs), with the important difference that these glasses can exhibit certain plastic strain prior to the catastrophic failure. Here...
Chapter
Beginning with a description of the prime mechanisms of fracture, i.e., cleavage, quasi-cleavage, intergranular cracking and microvoid coalescence, and then the crack-tip stress and strain fields which provide the driving forces to promote such fracture modes, this chapter explores the use of micromechanics to model mechanisms of fracture, beginnin...
Chapter
This chapter presents a concise description of nonlinear-elastic fracture mechanics, starting with Hutchinson, Rice, Rosengren (HRR) singularity and the definitions of the J-contour integral in terms of a characterizing parameter of the HRR crack-tip stress and displacement fields, a path-independent integral, and as a rate of change in potential e...
Chapter
This chapter provides a brief description of the origins of fracture mechanics and the methodology that preceded it. It describes the estimation of the ideal (theoretical) fracture strength to separate two planes of atoms, which is known to overestimate the experimentally measured cohesive strength of materials by more than an order of magnitude, b...
Chapter
This chapter explains how fracture mechanics can be applied to subcritical crack growth, primarily by environmentally-assisted cracking, creep, and fatigue. It describes in each case the development of a crack-growth relationship characterizing the velocity of a crack, with respect to time or number of cycles, as a function of the relevant governin...
Chapter
This chapter provides several descriptions and worked examples of the use of fracture mechanics in practice. Examples include the choice of steel for a support rod, the leak-before-break concept applied to pressure vessels, the failure of pre-tensioned bolts, and the development of a fracture control plan for estimating the safe life of medical hea...
Chapter
This chapter presents a concise description of linear-elastic fracture mechanics, starting with the 1/r crack-tip stress singularity and the definition of the stress-intensity factor K to define the crack-tip stress distribution in a linear-elastic solid. Solutions for the crack-tip stress and displacement fields in mode I, II, and III are tabulate...
Chapter
This chapter presents a description of the crack-tip opening displacement (CTOD) as an alternative measure of the fracture toughness in the presence of plasticity. In addition to its definition and relationship to the plastic-zone size, a description is given on how it can be experimentally measured as a basis of a criterion for the onset of fractu...
Article
Letter concerning the toughness of the scales of Arapaima gigas fish and how they provide protection against predator attacks.
Article
The brown pelican (Pelecanus occidentalis) wields one of the largest bills of any bird and is distinguished by the deployable throat pouch of extensible tissue used to capture prey. Here we report on mechanical properties and microstructure of the pouch skin. It exhibits significant anisotropy, with the transverse direction having maximum nominal t...
Article
Full-text available
Nacre's structure-property relationships have been a source of inspiration for designing advanced functional materials with both high strength and toughness. These outstanding mechanical properties have been mostly attributed to the interplay between aragonite platelets and organic matrices in the typical brick-and-mortar structure. Here, we show t...